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TWENTIETH CENTURY HAND-BOOK 

= FOR = 

STEAM ENCINEERSandELECTRICIANS 



WITH QUESTIONS AND ANSWERS 



A PRACTICAL NONTECHNICAL TREATISE 

On the Care and Management of Steam Engines, Boilers 
and Electric Machinery. With full instructions in 
Regard to the Intelligent Management of all Classes 
of Steam Engines, Steam Turbines, Gas Engines, Air 
Compressors and Elevators, both Electric and Hy- 
draulic. CThe section on Electricity is of especial 
importance to all engineers. : : : : : 



By CALVIN Fi SWINGLE, M. E. 

Author of "Encyclopedia of Engineering," "Examfnation Questions 

and Answers for Marine and Stationary Engineers," "Modern 

Locomotive Engineerijig," and "Modern Steam Boilers." 



LLUSTRAXED 



CHICAGO 

FREDERICK J. DRAKE & COMPANY 

PUBLISHERS 



1 J 277 

\ > v3 



Copyright 1903 

BY 

CALVIN F. SWINGLE 



Copyright 1907 
> BY 
FREDERICK J. DRAKE t^ €^. W-;^ 



Copyright 1910 

BY 

FREDERICK J. DRAKE & CO. 



Copyright 1913 

BY 

FREDERICK J. DRAKE & CO. 



,, /^ 



/■^\ rM * t-k ?»■ O r» PJ* /> 



INTEODUCTIOK 

Owing to the very generous reception accorded the iirst^ 
and second editions of the 20th Centnry Hand Book for 
Steam Engineers; there having been over one hundred 
tlionsand copies sold^ the author was urged to revise^ and 
greatly enlarge the present edition, tlius making it in a 
sense an encyclopedia of practical information, covering 
each department of vrork in which the stationary engineer 
is likely to be called upon to engage in the pursuit of 
his calling. In order to obtain a practical working knowl- 
edge of steam engineering it is absolutely necessary that 
the young man who desires to. become a successful engineer 
should start in the boiler-room, that he should thoroughly 
familiarize himself with all of the details of boiler manage- 
ment, and while his hands and eyes are thus gradually being 
trained to the practical part of the work he should at the 
same time be training his mind in the theoretical part by 
reading and studying technical books and journals relative 
to steam engineering. 

Without a doubt the most successful operating engineers 
are those who combine, practice with theory, but the en- 
gineer in charge of a steam plant should, in addition to 
his other accomplishments, have at least sufficient technical 
knowledge to enable him to ascertain, by measurements 
and calculations, such very important points as the safe 
working pressure of his boiler,, the most economical point 
of cut off for his engine, whether engine and boiler are 
properly proportioned for the work to be performed, and 
many ether details requiring his attention. 

In the following pages the author proposes to deal mair^^'' 



with the operation of steam engines^ boilers^ feed pumps, 
and all the necessary adjuncts of a steam plant, while at 
the same time considerable space will be devoted to the 
design, construction, and erection of steam machinery. Gas 
engines, Air compressors, and Elevators^ both electric and 
hydraulic. In the compilation of the section on Electricity 
for engineers, special efforts have been put forth to adapt 
the discussion of this important subject to the needs of 
engineers, and electricians in charge of central stations ; 
or isolated plants of smaller capacity. Within the past 
ten years there has been introduced a comparatively new 
prime mover, in the shape of the steam Turbine, and judg- 
ing from present indications it has come to stay. Therefore 
it behooves engineers to make themselves acquainted with 
it, and the sooner they do so the more will they be benefited 
by the advent of this stranger. In these pages the au- 
thor presents to his readers a plain practical description of 
each of the leading types of steam Turbines now in use, 
including an explanation of the principles controlling their 
action, together with rules and instructions for guidance 
in their operation. In order to facilitate the study of the 
different subjects treated upon, a series of practical ques- 
tions and answers will follow the close of each section. 
And now with the hope that a study of the , following pages 
may prove to be a help to all into whose hands this book 
may come, the author respectfully dedicates it to his fellow 
craftsmen, the engfineers of America. 

Calvin F. Swingle. 



\ 



The Boiler 



Stationary boilers may be divided into four different 
classes. The- first and most simple type, and the one from 
which the others have gradually evolved, is the plain cylin- 
der boiler in which the heated gases merely pass under the 
boiler^ coming in contact only with the lower half of the 
shell and then pass to the stack. These boilers are generally 
of small diameter (about 30 in.) and great length (30 ft.). 




Fig. 1 
return tubular boiler — showing setting 

Next comes the flue cylindrical boiler, which is somewhat 
larger in diameter than the former, generally 40 in. diam- 
eter and 20 to 30 ft. long, with two large flues 12 to 14 in. 
diameter extending through it. The return tubular boiler, 

1 



steam Engineering 




Fig. 2 

front view of 250 h. p. c ah all horizontal boiler 



consisting of a shell with tubes of small diameter (2 to 4 in.) 
extending from head to head through which the hot gases 
from the furnace pass on their way to the stack. This 



Return Tubular Boiler 3 

boiler, which comes in the third class, is probably more ex- 
tensively used in the United States for stationary service 
than any other type. The fourth class comprises the water 
tube boilers, in which^the water is carried in tubes 3 to 4 
in. in diameter, sometimes vertical and sometimes inclined, 
and connected at the top to one end of a steam drum, and 
having the lower ends of the tubes connected to a mud 
drum, which is also connected to the opposite end of the 
steam drum, thus providing for a free circulation of the 
water. Of the latter type there have been many different 
kinds evolved during the last one hundred years, the ma- 
jority of them having had but a brief existence, being com- 
pelled to obey the inexorable law of the survival of the 
fittest, and to-day there are a few excellent types of water 
tube boilers which have become standard and are being ex- 
tensively used. The margin of safety as regards disastrous 
explosions appears to be in favor of the water tube boiler. • 
It is not contended that they are entirely exempt from the 
danger of explosion. On the contrary, the percentage of 
explosions of water tube boilers in proportion to the num- 
ber in use is probably as large, if not larger, than it is with 
boilers of the shell or return tubular type, but the results 
are seldom so destructive of life or property, for the reason 
that if one or more of the tubes give way the pressure is 
released and the danger is past. 

THE CAHALL V^ATER TUBE BOILER. 

Figures 2 and 3 show, respectively, front and side views 
of the Cahall horizontal water tube boiler. These boilers 
are built in sizes of from 125 horsepower up to 850 horse- 
power, in single units. The boilers are built for working 
pressures of from 160 pounds per sq. in. up to 500 pounds 



4 Steam Engineering 

per sq. in. The steam drums are made of the best open 
hearth flange steel, the heads for the drums being of the 
same material, hydraulically flanged. All the sheets are 
beveled on the edges, bent into shape, and the rivet holes 
drilled after bending. This insures absolutely round holes, 
without crystallization, and allows calking of all seams, both 




Fig. 3 

SIDE VIEW OF 250 H. P. C AH ALL HORIZONTAL BOILER SUSPENDED 
READY FOR BRICK WORK 



inside and outside. In boilers, the working pressure of 
which is not to exceed 160 lbs. to the sq. in., the longitudinal 
seams in the drums are double riveted. In those of higher 
working pressures, that is, from 160 to 500 lbs. per sq. in.^^ 
3,11 of the horizontal seams are butt and double strapped 
joints, with six rows of rivets. Each drum is provided at 
both ends with the Cahall patent swinging man-head. The 



Cahall Water Tube Boiler 5 

action of this man-head is as follows: By loosening the 
nnts^ a slight push swings the head in similar to a door, 
and when it is desired to again close it, it is pulled back to 
its place, and, owing to its being hinged, the seats come to- 
gether in exactly the same place every time, thus insuring 
a tight* joint. The flanges on the steam drums for the 
steam and safety valve openings are all drop forged, from 
flanged steel plates. Eeferring to Figure 3, it will be 
noticed that each section of tubes is connected by nipples 
to saddles on the steam drums. These saddles or cross 
boxes are made from open hearth steel, which is melted 
and run into molds. This steel, after cooling and anneal- 
ing, presents all the chemical and physical properties of 
regular boiler plate steel, physical tests on a large number 
of coupons from these forms showing an elongation of over 
25 per cent, a reduction in area of over 50 per cent, with a 
tensile strength of over 60,000 lbs. to the square iijch. 

It can be seen from the side view of the boiler (Fig. 3) 
that it stands on wrought iron supports and cross beams, 
independent of the brickwork, so that the entire structure 
is free to contract and expand without any strains occurring 
either on the setting or on the boiler itself. In this method 
of suspension, the entire framework is outside of the brick- 
work, thereby avoiding the possibility of its burning aw^ay 
or weakening through over-heating, as has frequently hap- 
pened in the case of other designs. 

The fronts for the boiler are what is known as the wrought 
iron style — that is, the entire general framework of the 
front is made up of wrought iron or steel beams, channels 
and girders, and only the panels containing the door frames 
are cast. This permits of a very light but rigid structure, 
which it is impossible to crack from the application of in- 



steam Engineering 




Fig. 4 

bear view of 250 h. p. c ah all horizontal boiler suspended 

ready for brick work 



Cahall Water Tube Boiler 7 

ternal heat^ which has been heretofore one of the greatest 
faults found with this type of boiler. 

All the tubes used in this boiler are made of the best 
knobbled charcoal iron^ which though very much more ex- 
pensive than the standard iron boiler tube^ yet repays the 
customer in future years for the additional investment in 
first cost. The general fittings and trimmings of the boiler 
are of the highest grade purchasable^ the safety valves being 
of the solid nickel seated type. The water column used is 
either the Eeliance or Pittsburg High and Low Water 
Alarm. The blow-off valves are specially made under 
patents owned by the Aultman & Taylor Machinery Co., 
and are so designed that the discs are renewable at any 
time, and both the disc and valve seat can be cleaned with- 
out taking the valve apart. 

It will be noticed in the illustration (Fig. 4) giving the 
rear view of the boiler that these valves have two wheels, 
one directly above the other, the upper one being smaller 
than the lower. The larger wheel forces the disc down on 
its seat, the smaller wheel revolves the spindle carrying the 
disc. By revolving the larger wheel until the disc rests 
lightly on its seat and then revolving the smaller wheel, the 
disc is rotated on its seat, effectually clearing it of any ob- 
structions that may have accumulated thereon. 

The side cleaning doors for the boiler are of a new de- 
sign, which permits the use of only one door instead of 
two, and when the door is opened it is thrown back entirely 
from the slot into which it fits, leaving a full, free opening 
for the introduction of the steam hose, and when the door 
is closed, wedge-shaped fire-brick tile, which line the door, 
are pushed fprward in a straight line into the opening, 
making a perfectly smooth wall on the inside and an abso- 



8 Steam Engineering 

lutely tight joint against the leakage of air into the setting. 
Where very high pressures are to be nsed^ say in excess 
of 225 pounds to the square inch^ the headers or manifolds 
for the reception of the tubes are made of the same material 
used in the cross-boxes on the drums, viz._, special "flowed^^ 
steel. 

THE HEINE SAFETY BOILER. 

Figure 5 shows a general view of the Heine water tube 
boiler. 

The boiler is composed of the best lap welded wrought 
iron tubes, extending between and connecting the inside 
faces of two ^Vater legs/^ which form the end connections 
between these tubes and a combined steam and water drum 
or ^^shell/^ placed above and parallel with them. (Boilers 
over 200 horsepower have two such shells.) These end 
chambers are of approximately rectangular shape, drawn 
in at top to fit the curvature of the shells. Each is composed 
of a head plate and a tube sheet, flanged all around and 
joined at bottom and sides by a butt strap of same material, 
strongly riveted to both. The water legs are further stayed 
by hollow stay holts of hydraulic tubing, of large diameter, 
so placed that tAvo stays support each tube, and hand hole 
and are subjected to only very slight strain. Being made 
of heavy metal, they form the strongest parts of the boiler 
and its natural supports. The water legs are joined to 
the shell by flanged and riveted joints and the drum is 
cut away at these two points to make connection with inside 
of water leg, the opening thus made being strengthened 
by bridges and special stays, so as to preserve the original 
strength. 

The shells are cylinders with heads dished to form 



Heine Safety Boiler 9 

parts of. a true sphere. The sphere is everywhere as strong 

as the circle seam of the cylinder which is well known 

to be twice as strong as its side seam. Therefore these 

heads require no stays. Both the cylinder and its spherical 




Fig. 5 

375 H. p. HEINE BOILER 



heads are therefore free to folloiv their natural lines of 
expansion when put under pressure. Where flat heads 
have to be braced to the sides of the shelly, both suffer local 
distortions where the feet of the braces are riveted to them, 
making the calculations of their strength fallacious. To 



10 Steam Engineering 

the bottom of the front head a flange is riveted into which 
the feed pipe is screwed. This pipe is shown in the cut 
with angle valve and cliech valve attached. 

On top of shell -near the front end is riveted a steam noz- 
zle or saddle^, to which is bolted a tee. This tee carries the 
steam valve on its branchy which is made to look either to 
fronts rear^ right or left; on its top the safety valve is 
placed. The saddle has an area eqnal to that of stop valve 
and safety valve combined. The rear head carries a How- 
of flange of abont the same size as the feed, flange, and a 
manhead curved to fit the head, the manhole supported by 
a strengthening ring outside. On each side of the shell 
a square bar, the tile-bar, rests loosely in flat hooks riveted 
to the shell. This bar supports the side tiles whose other 
ends rest on the side walls, thus closing in the furnace or 
flue on top. The top of the tile bar is two inches below 
loiu water line. The bars rise from front to rear at the rate 
of one inch in twelve. When the boiler is set, they must 
be exactly level, the whole boiler being then -on an incline, 
i. e., with a fall" of one inch In twelve from front to rear. 
; It will be noted that this makes the height of the steam 
space in front about two-thirds the diameter of the shell, 
while at the rear the water occupies tiuo-thirds of the shell, 
the whole contents of the drum being equally divided be- 
tween steam and water. 

The tubes extend through the tube sheets into which 
they are expanded with roller expanders; opposite the end 
of each and in the head plates is placed a hand hole of 
slightly larger diameter than the tube, and through which 
it may be withdrawji. These hand holes are closed by small 
cast iron hand hole plates, which can be easily removed 
for the purpose of cleaning or inspecting a tube. Figure 



Heine Safety Boiler 



11 




Fig. 6 

detail of water- leg, hand hole plates and yokes, etc., of 

heine boilers 



12 



Steam Engineering 




Fig. 7 
side sectional view of heine boiler 



6 shows these hand hole plates, marked H. In the upper 
corner one is shown in detail, H^ being the top view, and 



Heine Safety Boiler 13 

H^ a side view^ while H^ is the yoke or crab placed outside 
to support the bolt and nut. Fignre 7 is a longitudinal 
section showing inside construction. The mud drum D is 
located well below the water line^ parallel to and three 
inches above the bottom of the shell. It is of oval section, 
slightly smaller than the manhole. It is entirely enclosed, 
except about eighteen inches of its upper portion at the 
front end, which is cut away nearly parallel with the water 
line. The mud drum D is made of strong sheet iron, with 
cast iron heads, and its action is as follows : 

The feed water enters it through the pipe F about one- 
half inch above its bottom ; even if it has previously passed 
the best heaters it is colder than the water in the boiler. 
Hence it drops to the bottom, and, impelled by the pump 
or injector, passes at a greatly reduced speed to the rear 
of the mud drum. As it is gradually heated to near boiler 
temperature it rises and flows slowly in reverse direction 
to the open front of the mud drum ; here it passes over in a 
thin sheet and is immediately swept backward into the 
main body of water by the swift circulation, thus becom- 
ing thoroughly mixed with it before it reaches the tubes. 
During this process the mud, lime, salts, and other precipi- 
tates are deposited as a sort of semi-fluid "sludge^^ near 
the rear end of the mud drum, whence it is blown off at 
frequent intervals through the blow-off valve N. As the 
speed in the mud drum is only about one-fiftieth of that in 
the feed water pipe, plenty of time is given for this action. 
Any precipitates which may escape the mud drum at firsts 
will of course form a scale on the inside of the tubes, etc. 
But the action of expansion and contraction cracks off scale 
on the inside of a tube much faster than on the outside, 
and then the circulation sweeps the small chips, like broken 



14 Steam Engineering 

egg-shells^ upward^ and as they pass over the mouth of the 
mud drum they drop in the eddy, lose velocity in this slow 
current and fall to the bottom^ and^ being pushed by the 
feed current to the rear end^ are blown off from the mud 
drum with other refuse. On opening a Heine boiler after 
some months^ service^ such bits of scale^ whose shape identi- 
fies them, are always found in the mud of the mud drum. 
Very little loose scale is found on the bottom of the water 
legs ; the current through- the lower tubes, always the swift- 
est, brushes too near the bottom to allow much to lodge 
there. 

This explanation of the action of the mud drum shows 
how the inside of the tubes may ie kept clean. To keep the 
outside clear of soot and ashes which deposit on, and some- 
times even bake fast to the tubes, each boiler is provided 
with two special nozzles, with both side and front outlets, a 
short one for the rear, a long one for the front. They are 
of three-eighth inch gas pipe and each is supplied with 
steam by a one-half inch steam hose. The nozzle is passed 
through each stay bolt in turn, and thus delivers its side 
jets on the three or four tubes adjacent, with the full force 
of the steam, at the short range of two inches, knocTcing the 
soot and ashes off completely, while the end jet carries 
them into the main draft current, to lodge at points in 
breeching or chimney base convenient for their ultimate 
removal. An inspection of the cuts will show that the 
stay bolts are so located that the nozzle can in turn be 
brought to bear on all sides of the tubes. As soon as the 
nozzle is withdrawn from the stay bolt this is closed air- 
tight by a plain wooden plug. 

In cleaning a boiler it is only necessary to remove every 
fourth or fifth handhole plate in the front water leg; the 



Heine Safety Boiler 15 

water hose, supplied with a short nozzle, can be entered in 
all the adjacent tubes, owing to the ample dimensions of 
the water leg. In the rear water leg only one or two hand- 
holes in the lower row need be opened to let the water and 
debris escape. The others in rear water leg are frequently 
left untouched for years. A lamp or candle hung on a 
wire through the manhead may be held opposite each tube 
so that it can be perfectly inspected from the front. 

The feed pipe F enters the mud drum through a loose 
joint in front, and the blow-off pipe K is screwed tightly 
into its rear head, passing by a steam-tight joint through 
the rear head of the shell. Just under the steam nozzle is 
placed a dry pipe A. L is a deflection plate, extending 
from the front of the shell, and inclined upwards, beyond 
the mouth of the front water leg. The throat or mouth 
of each water leg is large, to equal in area the total tube 
area, and where it joins the shell it increases gradually in 
width by double the radius of the flange. In the setting, 
the front water leg is placed firmly on a set of strong 
cast iron columns, bolted and braced together by the door 
frames, dead plate, etc., forming the fire front. This is the 
fixed end. The rear water leg rests on rollers, free to 
move on cast iron plates set in the lower masonry of the 
rear wall. The brick work does not close in entirely to 
the boiler, the space between being filled with tow or waste 
saturated with fire clay or other refractory, but pliable 
material, thus leaving the boiler and its walls each free 
to move separately during expansion or contraction, with- 
out disturbing any joints in the masonry. On the lower, 
and between the upper tubes, are placed light fire brick 
tiles. The lower tier extends from the front water leg to 
within a few feet of the rear one, leaving there an upward 



16 Steam Engineering 

passage across the rear ends of the tubes for the flame and 
gases. The upper tier closes into the rear water leg^ and 
extends forward to within a few feet of the front onC;, thus 
leaving an opening for the gases in front. The side tiles 
extend from the side walls to tile bars, and close up to the 
front water leg, and front wall, and leaye open the final 
uptake for the waste gases over the back part of the shell, 
which is here covered above the water line with a row of 
lock fire brick, resting on the tile bars. The rear wall, and 
one parallel to it, are arched over the shell a few feet for- 
ward, and form the uptakes. 

THE BABCOCK & WILCOX WATER TUBE BOILER. 

Description. Figure 8 presents a side view of the Bab- 
cock & Wilcox boiler, and Figure 9 a partial section. 

This boiler is composed of lap-welded wrought iron tubes, 
placed in an inclined position and connected with each 
other, and with a horizontal steam and water drum, by 
vertical passages at each end, while a mud-drum is con- 
nected to the rear and lowest point in the boiler. 

The end connections are in one piece for each vertical 
row of tubes, and are of such form that the tubes are ^^stag- 
gered^^ (or so placed that each row comes over the spaces 
in the previous row). The holes are accurately sized, made 
tapering, and the tubes fixed therein by an expander. The 
sections thus formed are connected with the drum, and 
with the mud-drum also by short tubes expanded into 
bored holes, doing away with all bolts, and leaving a clear 
passageway between the several parts. The openings for 
cleaning opposite the end of each tube are closed by hand- 
hole plates, the joints of which are made in the most thor- 
ough manner, by milling the surfaces to accurate metallic 



Bab cock and Wilcox Boiler 



17 




Fig. S 

side view of babcock & wilcox boiler of wrought steel 

construction 



18 Steam Engineering 

contacts, and are held in place by wrought-iron forged 
clamps and bolts. They are tested and made tight under 
a hydrostatic pressure of 300 pounds per square inch^ iron 
to iron, and without rubier packing or other perishable 
subsfances. 

The steam and water drums are made of flange iron or 
steely of extra thickness^ and double riveted. They can 
be made for any desired pressure^ and are always tested 
at 50 per cent above the pressure for which they are con- 
structed. The mud-drums are of cast iron, as the best 
material to withstand corrosion, and are provided with 
ample means for cleaning. 

Erection. In erecting this boiler, it is suspended entirely 
independent of the brickwork, from wrought iron girders 
resting on iron columns. This avoids any straining of the 
boiler from unequal expansion between it and its enclosing 
walls, and permits the brickwork to be repaired or re- 
moved, if necessary, without in any way disturbing the 
boiler. All the fixtures are extra heavy and of neat designs. 

Operation. The fire is made under the front and higher 
end of the tubes, and the products of the combustion pass 
up between the tubes into a combustion chamber under the 
steam and water drum; from thence they pass down be- 
tween the tubes, then once more up through the spaces be- 
tween the tubes, and off to the chimney. The water inside 
the tubes, as it is heated, tends to rise towards the higher 
end, and as it is converted into steam — the mingled col- 
umn of steam and water being of less specific gravity than 
the solid water at the back end of the boiler — rises through 
the vertical passages into the drum above the tubes, where 
the steam separates from the water and the latter flows 
back to the rear and down again through the tubes in a eon- 



Babcoch and Wilcox Boiler 



la 




Fig. 9 
partial vertical section babcock & wilcox boiler 



20 



Steam Engineering 



tinuous circnlation. As the passages are all large and 
free^ this circulation is very rapid, sweeping away the 
steam as fast as formed, and supplying its place with wa- 




FiG. 10 

STANDARD FRONT OF BABCOCK & WILCOX BOILER 

ter; absorbing the heat of the fire to tlie best advantage; 
causing a thorough commingling of the water throughout 
the boiler and a consequent equal temperature, and pre- 



Stirling Water Tube Boiler 21 

venting^ to a great degree, the formation of deposits or 
incrustations upon the heating surfaces, sweeping them 
away and depositing them in the mud-drum, whence they 
are blown out. 

The steam is taken out at the top of the steam-drum 
near the back end of the boiler after it has thoroughly sep- 
arated from the water, and to insure dry steam, a per- 
forated dry-pipe is connected to the nozzle inside the drum. 

THE STIRLING WATER-TUBE SAFETY BOILER. 

The Stirling boiler, Figures 11 and 12, consists of three 
tipper or steam drums, each connected by a number of tubes 
(called a "bank'^) to a lower or mud drum. Suitably dis- 
posed fire tile baffles between the banks direct the gases into 
their proper course. Shorter tubes connect the steam spaces 
of all upper drums, also water spaces of front, 'and middle 
drums. The boiler is supported on a structural steel frame- 
work, around which is built a brick setting, whose only 
office is to provide furnace space, and serve as a housing to 
confine the heat. The entire front is of metal of appro- 
priate and artistic design. These parts, together with the 
usual valves and fittings, constitute the completed boiler, 
which represents the acme of simplicity and eliminates the 
complication of the older types. 

The drums vary from 36 to 54 inches in diameter and 
are made of the best open hearth flange steel. The plates 
extend the entire distance between heads, hence there are 
no circular seams. The longitudinal seams — which are 
double or triple riveted according to the working pressure 
to be carried — are so placed that they are not exposed to 
high temperature. The drum heads are hydraulically 
dished to proper radius; each drum is provided with one 



22 Steam Engineering 

manhole^ and the manhole plate and arch bars are of 
wrought steel ; four manhole plates, which can be removed 
in ten minutes^, give access to the entire interior of the 
boiler, and expose every tube end, rivet and joint. The 
drum interiors are perfect^ clear; there are no baffles, 
staj^s, tie-rods, mud pipes or other obstructions in them. 

The tubes are best lap-welded mild steel. They are 
slightly curved at the ends to permit them to enter the 
drums normally and to provide for free expansion of the 
boiler when at work. The tubes are expanded directly 
into reamed holes in tube sheets of the drums, hence the 
annular recess between tubes and the cast headers of some 
types of boiler is eliminated, and failure of tubes by pit- 
ting through corrosion, caused by accumulation of soot in 
these recesses, is avoided. There are no short nipples and 
no tube joints in places which can be reached only by joint- 
ed handles on the tube expander, rendering it impossible 
to determine when the tube has been properly expanded. 
In the Stirling boiler every tube end is visible and acces- 
sible. As the entire weight of boiler and contents is sup- 
ported on the steel frame work, cracking of the setting, 
due to unequal settlements, is obviated, and no blocking is 
needed when the brick work has to be repaired. The design 
of frame work can be modified to suit special conditions. 
The brick setting is so clearly shown in Figures 11 and 12 
that an extended description is unnecessary, j^o special 
shapes or other material not found in open market are need- 
ed. Any necessary repairs to the brick work can be made 
without disturbing the boiler connections. In the design of 
the Stirling furnace it will be seen by reference to Figures 
11 and 12, that a fire brick arch is sprung over the grates, 
and immediately in front of the first bank of tubes. The 




FIG. 11 

SECTIONAL SIDE ELEVATION OF THE STIRLING BOILER 
AND BAGASSE FURNACE. 



FIG. 12 

SECTIONAL SIDE ELEVATION OF THE STIRLING INDEPENDENTLY 

FIRED SUPERHEATER. 



t 



Stirling Water Tube Boiler 



23 



large triangular space between boiler fronts tubes and mud 
drum is available for a combustion chamber, and for instal- 
lation of sufficient grate surface to meet the requirements 
of the lowest grades of fuel. 

Baffles and Course of Gases, The baffle walls rest di- 
rectly upon the tubes, and guide the course of the gases up 
the front bank; down the middle and up the rear bank, 
thus bringing them into such intimate contact with the 



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FLAT TILE 2 INCHES THICK 




SECTION ON A-B 



Fig. 13 
elevation and section of firetile baffles in stirling boilers 

boiler surface that the heat is quickly and thoroughly ex- 
tracted from them. In no other boiler are the gases com- 
ipelled to travel as far before reaching the stack, and the 
effect upon economy is evident. The baffles are made of 
plain rectangular firetile carried in stock by all fire-brick 
dealers, in contrast to the special formed bricks (obtain- 
able only from the manufacturer) required by many types 



24 Steam Engineering 

of water-tube boiler. Another marked advantage of the 
Stirling baffles is that since no tubes pass between or 
through the tiles (see Pig. 13), they are not pried apart 
and made leaky by distorted tubes; they can be removed 
and replaced without disturbing a tube. Baffles built across 
the tubes, as in many boilers, are damaged by pulling a 
faulty tube through them, and can 'be repaired in but one 
way— by removal of every tube necessary to permit a man 
to crawl in and reach the^ defective spot. 

Simplicity, There are no details of complicated shape; 
no flat surfaces, tie-rods, water-legs, headers, return-bends, 
outside circulating pipes to plug up; no multitudinous 
handhole plates to be removed and packed with gaskets, 
or to be ground and scraped to a fit whenever boiler is 
opened; no baffles or mud pipes in the drums; no short 
nipples, seams exposed to heat, or parts inaccessible for 
cleaning. 

Expansion and Contraction, In the Stirling, the mud 
drum is not embedded in brickwork, but is suspended on 
the tubes which connect it with the upper drums. 

In consequence of this construction, not only may the 
mud drum with perfect freedom move an amount repre- 
senting the resultant expansion of the boiler, but any dif- 
ference in expansion between the individual tubes, such 
as caused when one side of the furnace is being cleaned 
and other side is excessively hot, is taken up by the curve 
in the tube. The boiler therefore stays tight, and is en- 
tirely free from the stresses and frequent leaks caused by 
unequal expansion of straight tubes rigidly connected at 
each end to headers, water-legs, or large drums. It will 
thus be seen that the bent tube performs in the boiler the 
same function as an expansion loop in a steam line. 



Stirling Water Tube Boiler 25 

Rapid Circulation. The path of the circulation in the 
Stirling is as follows : The water is fed into upper rear 
drum^ passes down the rear bank of tubes to the lower 
drum^ thence up the front bank to forward steam drum. 
Here the steam formed during passage up the front bank 
disengages and passes through the upper row of cross 
tubes into the middle drum, while the solid water passes 
through the lower cross tubes into middle drum, then 
down the middle bank to the lower drum, from which it is 
again- drawn up the front bank to retrace its former course 
until it is finally evaporated. The steam generated in the 
rear bank passes through cross tubes to the center drum. 

The temperature of gases in contact with the tubes will 
evidently be greatest at the bottom of the front bank, and 
gradually decreases as the gases proceed along their course 
to the breeching. Obviously then the velocity of water 
circulation and quantity of steam generated will be a max- 
imum in the front bank; in the rear bank there is a slow 
circulation downward equal to the quantity of water evap- 
orated in the other two banks. 

Eapid circulation is essential for the following reasons : 

(1) To keep all parts of the boiler at practically the 
same temperature, thus eliminating severe stresses due to 
unequal expansion. 

(2) To permit quick raising of steam and rapid re- 
sponse to sudden demands on the boiler capacity. 

(3) To sweep away from the heating surfaces all steam 
bubbles as fast as formed, and thereby prevent ^^steam 
pockets," which quickly burn out the tubes. This is so 
particularly the case where intense local heating occurs 
due to use of gas or oil fuel, that some types of boiler fairly 
(Well adapted to coal cannot be successfully used with these 
fuels. 



26 Steam Engineering 

The third requirement is met only indifferently or, not 
at all in those types of boilers in which tubes often num- 
bering as many as eighteen must discharge their entire con- 
tent of steam and water through a narrow water-leg^, or, 
worse still, through a single nipple whose cross section is 
equal to that of but one tube. At 150 pounds^ g^^ge one 
cubic foot of water, when converted into steam, will have 
a volume of about 151 cubic feet. In consequence of this 
great increase in volume, as soon as the boiler is forced, the 
nipple area becomes insufficient, steam pockets form in 
the lower tubes, which then become overheated, and buckle 
and leak, and finally burn out. So inadequate are these 
nipples and headers that recent experiments of M. Brull 
have shown that in boilers whose circulation is constricted 
hy nipples or narrow water-legs, the circulation in the up- 
per tubes reverses, that is, it goes from the front to rear 
instead of in the opposite way, as intended. In conse- 
quence of this, much matter suspended in the water is 
swept into the bottom tubes, which fact, in connection with 
the steam pockets, explains why those'^ tubes so rapidly fail. 

In the Stirling boiler there is no constriction of the cir- 
culation, as each tube discharges directly into the drums, 
without intervention of headers, nipples or water-legs. The 
nearly vertical position of the tubes also promotes rapid 
circulation, hence steam pockets cannot form, and a fruit- 
ful cause of interrupted service and tube renewals is thus 
eliminated. 

A most fruitful cause of burnt tubes is a piece of scale 
which becomes detached and falls on the bottom of the 
tube, and the spot under it is certain to burn out quickly, 
The Stirling is free from this source of tube destruction, 
because while the scale will not form in the hotter tubes 



Stirling Water Tube Boiler 27 

unless the boiler is neglected^ even if it does form owing to 
such neglect and a piece becomes detached^ it will slide 
down to the mud drun^ instead of lodging. 

Cleaning the Interior, By removing four manhole plates, 
which can be done in ten minutes, the entire boiler interior 
is accessible for cleaning. From the preceding discussion 
it is evident that the precipitates are settled into the mud 
drum, whence they are blown off at intervals; the scale is 
practically confined to the rear bank of tubes, and by reason 
of escaping the high temperatures it is soft and easily 
detached. Consequently it happens in most cases that only 
the rear bank needs cleaning each time the boiler is opened, 
while the others need only occasional attention. The scale 
is quickly and cheaply removed by a ^^turbine cleaner,^^ 
described and illustrated in the section on Boiler Opera- 
tion. 

Cleaning the Exterior. Ample cleaning doors are pro- 
vided both in the sides and rear of the setting, so that the 
exterior of the heating surfaces may be kept clean and all 
accumulations of soot, ashes, etc., blown off as rapidly as 
they form, by using a steam blower-pipe which is furnished 
with every boiler. 

Durability. By reason of the elimination of thick plates 
and riveted joints exposed to the fire; cast metal of all 
kinds; parts of irregular shape and uncertain strength; 
stresses due to unequal expansion, multitudes of caps, joints 
and nipples, and similar objectionable details, the Stirling 
boiler is free from parts liable to get out of order. The 
prevention of scale deposits in the hottest tubes; the per- 
fect facilities for keeping the boiler clean; the rapidity of 
water circulation and impossibility of forming steam 
pockets, all combine to protect the tubes against burning 



28 



Steam Engineering 



out. Hence the necessity .of repairs to the boiler itself is 
extremely remote. The setting is sim.ple and substantial 
and not subject to derangement other than the natural 
wear of surface lining. 

MAXIM WATER-TUBE BOILER. 

The Maxim water-tube boiler (Figs. 14 and 15) consists 
of two drums^ one above the other, connected by tubes. 




Fig. 14 
front elevation maxim boiler 



Maxim Water Tube Boiler 



29 



Each tube has two bends^ thns providing for nneqnal ex- 
pansion and contraction. The space between the tubes is 
greater than the diameter of the tubes^ so that any tube 
can be passed through the space between. The tubes, which 
are nearly vertical^ are arranged in parallel rows, the lower 




Fig. 15 
maxim boiler 

tube plates being cylindrical^ and the bottom end of every 
tube is opened to the lower drum^ thus enabling the flue 
dust, m^d and loose scale to drop away from the heating 
surface. There are no riveted joints exposed to the flames 
or fire gases, and there are no cylinders subject to external 
pressure. 



30 Steam Engineering 

The heating surface is arranged so as to break up the 
current of heated gases^ which travels three times the length 
of the tube^ the form and direction of the gas current being 
changed seven times between the furnace and chimney, 
to insure a low temperature to the escaping gases. 

The circulation is constant, the return circulation being 
provided for by a third set of tubes, which are subjected 
to the heat of the gases just before reaching the chimney. 
As the cold feed water meets the gases as they leave the 
boiler, the front section of the tube, which receives the 
feed water, acts as an economizer and puT-ifier. 

The furnace of this type of boiler is constinicted of fire- 
brick, and is built under the boiler. Between the furnace 
and each combustion chamber there is a throat contracted 
to the proper size for drafts, the purpose being to insure a 
better combustion by an intimate mixture of gases. The 
illustrations show a side view, sectional view through A B, 
and a front view. 

THE BIGELOW-HORNSBY W^ATER-TUBE BOILER. 

The American rights to manufacture the Hornsby wa- 
ter-tube boiler, which has been on the English market five 
years, were recently acquired by the Bigelow Company, of 
New Haven, Conn., hence in this country it will be known 
as the ^^Bigelow-Hornsby^^ boiler. It has been re-designed 
in a measure, to meet the requirements of American high- 
pressure practice. A general idea of its construction may 
be obtained from Fig. 16, which shows a section through 
the setting. It will be noted that the boiler is supported 
entirely from the overhead beams, leaving the lower part 
free to respond to expansion stresses. The front tubes are 
inclined at an angle of 68 degrees, and the rear units 



BigeloW'Hornsby Boiler 



31 




Fig. 16 
section through setting of bigelow-hornsby boiler 



are vertical^ as shown. Only two lengths of tubes are 

used. Each section is independent of its neighbor, except 

I the nipples connecting Avith the steam drum and the equal- 



32 Steam Engineering 

izing nipples which connect the bottom drums of the rear 
sections. This flexible form of construction permits the 
building of very large units^ even larger than the 2,200- 
horsepower Hornsby boilers at the Bow Street station of 
the Charing Cross & London Electricity Works, where four 
boilers Qontaining 21,700 square feet of heating surface 
evaporate in regular service 110,000 pounds of water per 
hour. A large percentage of ^he heating surface is exposed 
to the radiant heat of the furnace, and to the first pass of 
gases, before these have reached any other heating surface. 
The tubes of the front unit, which are located in front of 
the baffles, comprise more than 12 per cent of the heating 
surface of the boiler. 

The feed-water is admitted Into the bottom drum of the 
rear unit and is advanced gradually from the coldest to 
the hottest portion of the boiler, first passing up the entire 
length of the tubes in the rear unit, then from the top of 
those tubes to the unit immediately in front, down this 
unit, and up the two front units and back through the 
steam drum to the first vertical unit at the rear of the 
steam drum. There is also, as may be conceived, a rapid 
local circulation in each of the units while the general 
circulation is going forward. The speed of the feed-water 
up the rear unit being regulated by the amount of steam 
generated, ample time is permitted for sediment and scale- 
forming matter to be deposited in the bottom drum of 
this unit. All liberation of steam from the water sur- 
faces takes place in the upper drums and is entirely unre- 
strained, the full area of the tube openings communicating 
with the drums. The transfer of steam and water between 
units occurs through separate nipples, and the water nip- 
ples are required merely to care for the general circulation 
through the JDoiler. 



Bigeloiv-Hornsby Boiler 



33 



The arrangement of this boiler is such that it can be 
bafHed so that the products of combustion are carried uni- 
formly over the heating surfaces in thin layers^ there being 
no large unrestricted paths parallel to the heating surfaces 
through which the gases can flow in their passage to the 



^^fo^C^oo 




Fig. 17 



uptake. Fig. 17^ which is a horizontal section through 
some of the rear units, shows how they are arranged with 
reference to the gas currents, and how the baffle-plates 
serve to guide the gases through in substantially uniform 
passages. 



34 Steam Engineering 

The smoke flue can be taken off at the back of the boiler 
at any point between the top and bottom. All the tubes 
are straight and every tube in each section can be reached 
for cleaning by the removal of a single manhole cover. 

The boiler is built to a factor of safety of five for 200 
pounds working pressure, and it is stated that a test sec- 
tion has been subjected to hydrostatic pressure of 1,000 
pounds without rupture. The ratio of grate surface to 
heating can be made as low as 1 to 26. 

WICKES VERTICAL WATER-TUBE BOILER. 

This boiler (see Fig. 18) consists primarily of two cyl- 
inders joined together by straight tubes, which are divided 
by a fire brick tile passing through their center into two 
compartments. The whole is then erected in a vertical 
position and surrounded by brickwork. 

Drum, The two cylinders are duplicates in their diam- 
eter and general construction, but differ in height and ar- 
rangement of convexed heads. The top cylinder, desig- 
nated hereafter, from its use, as the steam drum, is the 
longer, the length and diameter being varied in accordance 
with the size of boiler desired and local requirements. 

The bottom cylinder, designated hereafter, from its use, 
as the mud drum, is the shorter, and is varied in the di- 
mension as to diameter and length in accordance with the 
power of boiler required and local conditions. Both drums 
are closed at one end with the tube sheet, and at the other 
end with convexed heads. 

Tubes. The mud and steam drums are joined together 
by the tubes, which are perfectly straight in ^themselves 
and plumb, in position, when expanded into the two tube 
sheets. They are arranged in parallel rows, from furnace 



Wickes Vertical Water Tube Boiler 



35 




Fig. 18 
wickes vertical water tube boiler 



to stack, with a clear space between rows sufficient to per- 
mit of introducing a small hoe for the purpose of removing 



36 Steam Engineering 

any deposit of soot or of sediment which has fallen from 
the tubes and accumnlated on the mud drum tube sheet. 

Manholes. In the convexed head of the steam drum 
one large manhole, and a number of handholes, are placed, 
and in the shell of the mud drum on a level with the floor 
another manhole is placed. 

This arrangement permits entering the boiler at the 
highest and lowest points b}^ simply breaking two joints, 
from which points an examination may be made, or the 
tubes cleaned. By the introduction of heavy fire clay tile, 
the tubes are divided into two compartments. The tubes 
in the forward compartment are called the ^^risers,'^ and 
those in the rear compartment the ^^downcomers,^^ since 
the heat, and the water, mingled with steam, rise in the 
forward tubes, and both heat and the water in a solid col- 
umn descend in those forming the rear compartment, the 
steam having passed into the upper drum. This gives the 
heat two complete sweeps through the entire length of the 
boiler, and the second sweep from above downward. The 
heat in its double passage surrounds completely and closely 
the tubes in both compartments. 

Vi-ater Line. The water line in this boiler is maintained 
in the steam drum, at a sufficient height to insure the com- 
plete submersion of the tubes. 

Bajfie Plate. On a level with the water line, and ex- 
tending over the tubes in the front compartment, is the 
baffle plate, which deflects the water of circulation rising, 
commingled with its steam, directly to the "downcomers,'' 
and without splashing and spraying the steam room direct- 
ly above with globules or 'masses of water. 

Liherating Surface. Fully two-thirds of the entire area 
of steam drum is liberating surface, and, as the liberation 



WicJces Vertical Water Tube Boiler 37 

takes place mainly over the ^^downcomers/^ it does so in the 
quietest manner and in the absence of violent ebullition or 
turmoil. 

Steam Room, The large steam room is therefore en- 
tirely free from water^ and the steam outlet is the topmost 
pointy which is far away from the water line^ in large boil- 
ers the distance being from six to seven feet. On the other 
hand^ the blow-off is at the very lowest pointy, and where 
all impurities are precipitated by gravity^ and by separa- 
tion due to the flow of the water of circulation. 

Feed Water, The feed water may be introduced in the 
steam drum directly into the "downcomers'^ and far below 
the water line^ or in the mud drum above the precipitated 
sediment. The latter method, viz., introducing the feed 
water into the mud drum is to be preferred. 

Setting. The brick work setting of the Wickes boiler is 
so arranged that it is entirely independent of the weight 
of the boiler, ^nd is therefore free to expand or contract as 
its co-efficient may dictate, thus allowing the boiler to ex- 
pand and contract in accordance with the special laws gov- 
erning its change of form. 

The gases of combustion are closely confined to the tubes, 
after their generation in the furnace, and on their passage 
to the stack. The direct flow of the heat is, by virtue of 
the draft over the tile, and down by the shortest possible 
route, or path of least resistance; while heat of radiation 
rises naturally and surrounds the steam drum which, as 
will be seen by reference to Fig. 18, is surrounded by brick 
work to its top seam. It is claimed by the manufacturers 
of this boiler that very dry steam is obtained from it, the 
upper drum acting as a superheater. A damper, either sin- 
gle or double wing, is placed in the setting at the point of 



38 Steam Engineering 

exit of the gases. It is so designed as to allow the qnick 
and easy removal of the wings when cleaning is going on. 
The foundation is so designed that by means of a door 
through the circular brickwork^ a man can enter under- 
neath the boiler^ examine the blow-off pipe and rivets^ and 
see that the bottom of the mud drum is kept well and heav- 
ily painted. 

ATLAS WATER-TUBE BOILER. 

The design and construction of the Atlas water-tube 
boiler will be easily comprehended by reference to Fig. 19, 
which presents a full view of this boiler before setting. It 
consists mainly of three drums, and two water-legs extend- 
ing crosswise, and the tubes running lengthwise. The rear 
water-leg is mounted on rollers in setting, in order to allow 
for expansion, and contraction of the tubes. 

An important and original feature in the general de- 
sign is, that the water-legs are formed by the continuation 
of the plates of which the shells of the front and rear 
drums are composed. Thus no flanged plates, or riveted 
seams whatever are exposed either to the fire or hot gases 
at any point. The value of this form of construction lies 
in the fact that it eliminates the possibility of the crystal- 
lization of plates and rivets and consequent cracks, and an- 
noying leaks at the seams arising from overheating and un- 
equal expansion and contraction of double metal thickness, 
due to exposure to flames and furnace gases of high tem- 
perature. 

Another exclusive and very valuable feature of the de 
sign is the arrangement for passing the steam, after leav- 
ing the vessels containing water, through a series of super^ 
heating tubes, wherein it loses every particle of moisture 



Atlas Water Tube Boiler 



39 




Fig. 19 
atlas water tube boiler 



40 Steam Engineering 

and is heated to a temperature many degrees higher than 
that normal to its pressure. 

Attention is directed to the fact that no matter how 
large the boiler^ there is only one steam drum^ consequently 
the entire product of the boiler can be piped out of a 
single steam opening. This means a large saving in the 
cost of piping when compared to the expense incident to 
installing other types of boilers^ which in units of^ say, 200 
horsepower, or larger, necessarily have two longitudinal 
drums to be connected together by the purchaser. 

All parts of the Atlas boiler and the fixtures furnished 
are designed for a safe working pressure of 160 pounds 
per square inch with a safety factor of more than 5. 

All materials have been selected with especial reference 
to their adaptability to the service required. The shells 
and heads of the drums and water-legs are open hearth 
homogeneous flange steel, bearing the maker's stamp of 
60,000 pounds tensile strength per square inch of section, 
with not less than 50 per cent of ductility as indicated by 
contraction of area at point of fracture under test; an 
elongation of 25 per cent in a length of 8 inches, and guar- 
anteed by the makers to be capable of bending down flat 
upon itself when cold, red hot or after being heated to a 
cherry red and quenched in cold water, without sign of 
fracture. The chemical and physical properties are deter- 
mined by thorough tests, and all plates must meet the re- 
quirements of the best accepted practice. 

The tubes are standard American lap welded, thoroughly 
tested in all particulars before being expanded into place 
by roller expanders and again after the boiler is assembled. 
The tube-holes are accurately placed by template, then 
reamed and neatly chamfered. 



Atlas Water Tube Boiler 41 

Double-refined iron staybolts and braces, having an ulti- 
mate tensile strength of 52,000 pounds per square inch of 
section, an elastic limit of at least half the tensile strength 
and an elongation of eighteen per cent in a length of 8 
inches, are set to bear uniform tension. 

The rivets are of mild steel and can be bent over cold 
till the sides meet, without developing cracks on the outside 
of the bent portion. All rivet holes are reamed to perfect 
fairness, and the riveting wherever practicable is done by 
hydraulic niachinery, upsetting the rivet its full length, 
completely filling the hole and forming a perfect head in 
line with it. There are no riveted seams in the fire, or in 
the path of the furnace gases. 

All heads are first heated to a uniform bright red and 
then flanged at a single operation in a hydraulic flanging 
press. The bends in the plates forming the bottoms of 
the water-legs are pressed cold under heavy pressure. There 
is no distortion, either of heads or plates and there is a 
total absence of marks resulting from frequent and partial 
heating and hammering into shape. 

No cast metals are used in any parts that are subjected 
to tensile stresses, or furnace heat. The cast iron that is 
used for handhole and manhole plates and yokes is good, 
soft, grey iron, free from flaws or imperfections. 

The rapid, steady, unimpeded flow of the water in the 
course natural to expansion by exposure to heating sur- 
face, bears important relation to the most economical utili- 
zation of the heat units in the furnace gases, and is an es- 
sential factor in the achievement of the highest efficiency 
in. the production of steam. Uniform temperature in all 
parts exposed to furnace heat, which is so necessary to the 
safety and durability of the boiler, cannot exist with faulty 
circulation. 



42 



Steam Engineering 




Fig. 20 
atlas water tube boiler — sectional view 



Atlas Water Tube Boiler 43 

The water is fed into the purifier, whence it overflows 
into the rear drum and passes down into the rear leg, 
thence through the inclined tubes to the front leg and up- 
ward into the front drum, where the globules of steam gen- 
erated in the tubes are liberated and carried through the 
superhfating tubes to the steam drum. Meanwhile the 
water continues its flow through the equalizing tubes to the 
rear drum, joining the feed current at that point. The 
regular movement of all the water in the circuit just de- 
scribed, indicates uniform temperature in all the water- 
tubes, and when an unimpeded circuit has been established 
in the manner just explained, a maximum supply of dry 
steam will be delivered. When the circulation is retarded 
to sluggishness, the water does not so readily absorb the 
heat, and wet steam and a smaller quantity of it must be 
expected. It will be noted that while the design of this 
boiler admits with equal facility the use of either the 
vertical or the horizontal flame travel, the illustrations here- 
with show the vertical, it being preferred for several 
reasons, not the least important of which is that a more 
uniform distribution of the heat arising from the grates 
is obtained by first passing the gases upward through the 
entire nest of tubes between the front end of the furnace^ 
and the first vertical bafHe, thence downward between the 
first and second baffles and finally upward again through 
the entire nest of tubes between the second baffle, and the 
rear water-leg. It is not difficult to understand that, 
aside from all other considerations, the course of the heat- 
ed gases as described ia conducive to a more nearly equal 
division of the units of heat among all the water-carrying 
tubes than is possible with the horizontal travel which 
concentrates by far the greatest degree of heat on the low- 



44 Steam Engineering 

est tubes during almost their entire length. Uniform heat 
distribution means uniform temperature, which logically 
followed leads to the reasonable belief that the circulation, 
which increases or decreases as the temperature goes up 
or down, is of regular direction in all of the tubes, and 
that each tube is doing its full share of the work. 

Superheated steam has of late years been the subject of 
much thought and experiment, and now the economical 
utility of steam containing a number of degrees of super- 
heat is quite generally understood. Ordinary steam at 
100 pounds gauge pressure has a normal temperature 
(omitting decimals) of 338° Fahr., and at 160 pounds its 
normal temperature is 370° Fahr. The temperature in 
excess of normal for steam of a given pressure is technic- 
ally designated superheat. Steam that is in contact with 
the water from which it was generated cannot be heated 
above the temperature normal to its pressure. The process 
of superheating must therefore take place subsequent to 
the passage of the steam from the vessels containing water. 
Superheat is obtained by exposing the steam to 'gases of a 
higher temperature. The number of degrees of superheat 
obtainable is governed by the temperature of the gases to 
which the steam is exposed, and the duration of the ex- 
posure. It is claimed for the Atlas water-tube boilers that 
during various 'tests under actual working conditions they 
have produced steam containing from 10 to 30 degrees of 
superheat. 

All users of steam are familiar with radiation losses in 
steam pipes and the wastes in engine cylinders due to the 
fact that, at each stroke the new supply of steam is 
brought into contact with the face of the piston and the 
internal surfaces of the cylinder, which have been cooled 



Atlas Water Tube Boiler 45 

by the exhaust of the previous stroke. When steam is 
used at normal temperature^, each degree of heat thus lost 
means condensation and a proportional decrease of pres- 
sure. When superheated steam is used there is no loss of 
pressure until the steam is cooled to the temperature nor- 
mal to the boiler pressure. Up to within the last few years 
it was customary to equip each boiler with a mud drum. 
Two very important facts^ however, militated so seriously 
against the mud drum that it is now eliminated from the 
best boiler practice. In the first place a dangerously large 
percentage of the substances in the feed water, which at 
high temperatures become insoluble, would not gravitate 
toward and settle within the mud drum according • to the 
plan laid out for them, and in the second place, the mud 
drum proved in many cases little short of an aggravation 
by reason of the constant and irremediable leakage of the 
joints between the drum and the boiler, due to greater ex- 
pansion and contraction of the boiler, the drum being nec- 
essarily situated outside of the current of the hottest gases. 

Fig. 20, which is a sectional view of the Atlas water- 
tube boiler as it appears set in brick work, shows a purify- 
ing device which is hung loosely by strap hooks inside the 
shell of the rear water drum, its depth gradually increasing 
toward the blow-off end. 

The water is fed into the shallow end and, the pan being 
large and always full of, and surrounded by, hot water 
and steam, it is raised to from 250° to 275° Fahr. before 
it overflows into the main portion of the drum. 

The overflow takes place entirely at the shallow end of 
the pan, the top of that head being one inch lower than 
the other head and the sides. It is a well-known fact that 
water begins to clear itself when it reaches a temperature 



46 Steam Engineering 

of 200° Fahr._, and as the liberal dimensions of the pan 
allow the water to remain in it a considerable time, prac- 
tically all the scale-forming impurities are precipitated 
to the bottom of the pan where they remain in a soft 
sludge-like state pending the opening of the blow-off valve, 
the frequency of which should be governed by the character 
of the water and the rapidity of the accumulation. 

It will be noted that aside from its open top, which is 
several inches above the water line in the boiler, the pan 
is water-tight. It is entirely practicable, therefore, to blow 
off the sediment as often as desirable while the boiler is 
under pressure without fear of reducing the water level 
below the point of safety. 

Corrosion is one of the inevitable effects of the accumu- 
lation of mud and sediment on metal. Unlike purifiers 
common to some other boilers, which consist of a pocket- 
shelf built against the shell or one head of the boiler itself, 
which, therefore, forms part of the purifier and is exposed 
to the corrosive action of its contents, the purifier in the 
Atlas boiler is self-contained and absolutely independent 
of the boiler-shell or heads. The pan is made in sections 
and when it finally deteriorates to an unserviceable point, 
can be removed and replaced through the manhole with 
little labor and small expense. 

It is estimated that an incrustation of jV-i^ch will cause 
a loss of 13 per cent of fuel, %-inch 25 per cent, and so 
on, and these figures are probably not far from correct. 
Therefore, the purification of the feed water before it 
reaches the surfaces exposed to the baking heat of the 
furnace tends to a more economical use of fuel. It also 
reduces cleaning labor and the cost of repairs and increases 
the life of the boiler by avoiding the early disintegration 



Atlas Water Tube Boiler 



47 



of the metal which results from subjecting it to that intense 
heat necessary to boil water through the additional thick- 




FiG. 21 

ATLAS WATER TUBE BOILER 

Section through Rear End Showing Water Purifier 

ness due to a coating of scale. An individual hand-hole is 
located opposite each end of each water tube. 



48 Steam Engineering 

These hand-holes are of the diamond-oval shape^ having 
an accurately fitting plate^ held in position by a suitable 
yoke with bolt and nut^ the construction being such that 
the pressure on the inside of the boiler maintains the tight- 
ness of the joint. Any one of these plates can be removed 
and replaced through its own opening without disturbing 
any of the others. The water tubes in this boiler being 
absolutely straight^ in order to clean them thoroughly on 
the inside^ it is only necessary to remove the front hand- 
hole plates, insert a scraper and push the sediment back 
into the rear water-leg^, from which it may be easily re- 
moved through a few of the hand-holes in the bottom row, 
or through the blow-off. The internal condition of each 
water tube may be determined without removing any of 
the rear hand-hole plates by suspending a light through 
the full length throat between the rear water-leg and 
drum, and holding it in turn opposite the rear end of each 
water tube, while looking through the open hand-holes in 
front. Or, if the engineer prefers, the top row of rear 
hand-hole plates may be removed, and the light inserted 
and suspended, without entering the drum. 

The interior of each of the three cross drums of the 
Atlas boiler is reached through a large manhole in one 
end. The edge of this manhole forms a deep flange at 
right angles with the head, is faced true and provided with 
an accurately fitted plate with yokes, bolts and nuts, all of 
such proportions that this part of the head is as strong 
as any other of like area. 

MARZOLF WATER-TUBE BOILER. 

Another design of water-tube boiler is shown in Fig. 22. 
The object has been to construct a boiler so that the rela- 



Marzolf Water Tube Boiler 49 

tive arrangements of the tubes^ drum^ and heat passages 
are such as to obtain the most economical distribution of 



Fig. 22 
marzolf boiler — sectional view 

heat. Another object is to facilitate the heating of the 
water^ and increase the circulation by arranging the drums. 



50 Steam Engineering 

and a series of tubes so as to receive the direct applica- 
tion of the heat from the furnace. 

As shown^ the drum A is located in the furnace and 
connected to the drum B by tubes slightly bent at each end^ 
the drums A and B being connected to the drum C by simi- 
lar tubes. As the flame and hot gases rise from the furnace^ 
they surround the water drum A and^ striking the arch or 
baffle wall D^ follow along the inclined tubes E^ which re- 
ceive the direct application of the heat generated by the 
combustion of the fuel. The extension of the bridge wall 
is reduced in thickness above the grate^ as shown at F^ 
forming a back wall which rises vertically behind the water 
drum A^ to a point close beneath the series of tubes E. 
This wall is surmounted by a sloping wall G^ which stands 
adjacent to^ and parallel with^ the tubes E^ and extends 
toward the drum B. Owing to the baffle wall H, the hot 
gases are -forced up along the tubes E^ and down through 
the tubes I to the heating chamber K^ the roof of which is 
found by the baffle wall H. The baffle wall L is inclined 
downward parallel to and close to the rear of the series 
of tubes J from a point directly behind the steam 
drum B^ to a point over the mud drum C^ whereby the 
heat and products of combustion are deflected downwards 
among the tubes ^. v 

The hot gases pass from the heating chamber to the 
passage M between the lower end of the baffle wall and the 
mud drum C to a draft passage located between the baffle 
and the rear wall leading to the stack. 

The heat thus not only acts directly upon the water-drum 
A and upon the portions of the tubes IST and E^ located 
within the furnace^ but also upon the tubes E above the 
furnace^ upon the steam drum B, the tubes J and the mud 



Marzolf Water Tube Boiler 51 

drum C. The portion of the tubes N which lies within the 
heating chamber K also receives heat to some extent, al- 
though the heat does not act directly upon them as upon 
the other tubes. 

The feed water supply to this boiler is admitted through 
the drum C, and circulates through the tubes N^ water 
drum A, tubes E, steam drum B, and tubes J, back to the 
mud drum, making one continuous circuit. As shown by 
the illustration, the steam drum B is relatively larger and 
consequently of much greater capacity than either of the 
other two drums. It will be noticed that the tubes N" are 
placed on an incline, owing to the mud drum being lo- 
cated on a lower level than the water drum A, a design 
intended to cause all sediment carried into the boiler to 
gravitate to the mud drum C, from which it may be readily 
rem^oved through the usual blow-ofP. 

DUPLEX WATER-TUBE BOILER. ^ 

In the Duplex water- tube boiler, Fig. 23, the features 
which are most strongly emphasized b}^ the designers are: 
Delivery of steam from the boiler in a superheated condi- 
tion, without the use of a special superheater; removal of 
steam from the boiler at a point where there is no ebulli- 
tion, and elimination of a great many parts of the undu- 
lating header type of boiler. The design of the boiler shows 
absence of stay-bolted surfaces, the drums are not exposed 
to the direct action of the fire, all seams or rivets are en- 
tirely removed from contact with the heat, rigid connec- 
tions are avoided between parts, and all joints are ex- 
panded. 

The Duplex boiler consists of two upper steam drums 
connected by tubes. Short tubes expanded into the bottom 



steam Engineering 




Fig. 23 
duplex water tube boilek 



Duplex Water Tube Boiler 53 

of the shell of the rear drum form the connection to a set 
. of headers below it, which are connected to the front drum 
f by tubes expanded into the shell of the latter. This com- 
prises the upper generating system. These headers are 
; likewise connected to a drum situated below them by short 
: nipples, and this lower drum is in turn united to a set of 
; headers below, and similarly connected to, the front drum. 
! This comprises the lower generating system. The tubes are 
I inclined 20 degrees to insure rapid and positive circulation. 

I The drums are made in one sheet with no circular seams 
I except those connecting the heads to the shell. The longi- 
tudinal seams are butt-strapped, either double or triple 
riveted, as the pressure demands, and located on the out- 
side of the shell. A pressed-steel manhole is placed on 
the circumference of the shell for access to the interior of 
the drums. 

The headers are heavy, made of open-hearth steel, and 
the section of the header to which the hand-hole plates are 
secured is designed to be extra heavy, as is that portion 
where the tubes enter the header, this latter being intended 
to provide a wide tube seat and obviate the danger of leaky 
tube joints. The headers are of long box-like form and 
each header is designed to take in two vertical rows of 
tubes. An elliptical hand-hole is placed opposite the ends 
of two tubes through which the tubes are cleaned or re- 
moved. This hand-hole is closed by an elliptical cap inside 
the header held in position by a bolt secured with an out- 
side crab. The joint between the cap seat and the header is 
made tight with an asbestos gasket to avoid the necessity 
of remilling the contact surfaces eyexj time a cap is re- 



54 Steam Engineering 

moved and replaced. In this construction the bolt and 
crab are relieved of the strain of the boiler pressure. 

The boiler tubes are 3i/4 inches in diameter, of either 
charcoal-iron, or steel lap-welded, expanded directly into the 
shell of the drums or into the headers, and the ends are 
belled over one-quarter of an inch. 

A heavy steel framework incased in the brick setting 
supports the boiler. On the sides and independent of the 
boiler are built walls of brick about 17 inches in thickness. 
The rear of the boiler is fitted with a sheet-iron casing pro- 
tected with asbestos covering, the boiler being roofed over 
with fire-tile supported by heavy T-irons. The boiler fronts 
are of steel and doors of ornamental design are provided 
for access to the headers. The frame-work is so designed 
as to provide for the free expansion of all the tubes. The 
two upper drums are set on lugs secured to the heads, the 
lugs in turn being supported by the steel framework. The 
rear lugs are first set on rollers which allow for the ex- 
pansion of the tubes connecting the two drums. The hori- 
zontal style of baffling is used. These baffles rest on the 
tubes, and guide the gases along the lower bank, and the 
horizontal circulating tubes. 

Finally, the gases pass through the smoke outlet, which 
may be located on the top of the boiler at the rear, or at a 
point just under the rear drum. The course of the gases 
is always upward, which is the free and natural passage for 
them. The baffles are of the common rectangular shape, 
which any dealer carries in stock. The upper and lower 
banks of tubes comprise the active heating surface of this 
boiler. The tubes that form the lower system are con- 
nected at their rear ends to a large mud drum, which acts 



Duplex Water Tube Boiler 55 

as a reservoir for water to insure an ample supply for the 
bottom tubes at all times. The upper bank of tubes is 
arranged in reverse of the lower^ the tubes being connected 
to the front drums at their front ends. All the tubes of 
the upper system discharge independently into this drum. 
The header ends of both banks of tubes are connected into 
headers that are straight and of ample area. The tubes 
are of easy access for the purpose of scraping off soot that 
has been baked on in service. The feed water is introduced 
in the upper rear drum^ where any air that it contains may 
be liberated. It then passes downward through the rear 
circulating tubes and headers to the lower rear drum, where 
any impurities present in the feed water may be deposited. 

The passage of the water is then upward through the 
lower bank of tubes, through the front headers to the 
front drum. 

At this point any steam that is generated separates from 
the water, and passes across the steam tubes to the rear 
drum, and is believed to be thoroughly dried out, and 
slightly superheated in the process by coming in contact 
with the hot gases surrounding these tubes. The water 
passes across through the circulating, horizontal tubes to the 
rear drum, thence downward again to the rear headers, and 
thence up the upper bank of tubes into the front drum 
again. By this time it is expected that the watei* will 
have become heated to a very high temperature and, becom- 
ing steam, it passes to the rear drum through the super- 
heating tubes, becoming superheated on the route. 

From this rear drum the steam is withdrawn, there 
being no ebullition at this place, as experiment with a boiler 
with glass heads on the rear drum has shown. The safety 



56 Steam Engineering 

valve is located on the front drum^ where its sudden oper- 
ation cannot throw water into the steam opening. The 
spaces between the banks of tubes provide access to all 
parts of the boiler inside the setting through doors in the 
settings and other openings in the setting permit the boiler 
tubes to be cleaned by blowing with steam^ or compressed 
air. 

The builders of this boiler^ the Eobb-Mumford Boiler 
Company, of South Framingham, Mass., have been carry- 
ing on some very satisfactory experimental tests during 
the past year. 

ERIE CITY W^ATER-TUBE BOILER. 

The Erie City Iron Works, of Erie, Penn., has added 
to its line of products the boiler shown in the accompanying 
illustrations. Pigs. 24 to 26, the reproduced photographs 
shown being from the experimental boiler at the Erie 
shops. It is not claimed that the type is novel, but that 
the Erie iron works will bring to its manufacture and ex- 
ploitation refinements and improvement in detail and ex- 
perience and facilities which should soon make a place for 
it among the standard types. 

Unite the three banks of tubes of a Stirling boiler in a 
single upper drum, placed with its center directly over the 
center of the lower one, and you have the type. The fur- 
nace is an extension on the Dutch-oven plan, allowing 
great flexibility in the adjustment of grate to heating sur- 
face, and introducing the improved furnace conditions of 
the reverberatory arch. Additional capacity is gained by 
increasing the length of the drums and the number of 
tubes side wise, carrying with it increased width of fur- 



Erie City Water Tube Boiler 



57 




Fig. 24 
erie city water tube boiler 



nace and proportionate increase of grate surface, while 
the length of the grate may be made such as to give the 
• desired ratio of grate to heating surface. 



68 



Steam Engineering 



The tubes are so spaced that any one of them may be 
cut out, removed and replaced without interfering with 




Fig. 25 
side elevation erie city water tube boiler 



any other. The entire boiler is suspended, as the engrav- 
ings show, from the upper drum, giving perfect flexibility 



Erie City Water Tube Boiler 



59 



and freedom to adjust itself to varying conditions of tem- 
perature and stress. The sufficiency of the expanded tube 




Fig. 26 
ienlarged view showing separator in drum of erie city boiler 

[joints in the upper drum to s;iistain the weight thus brought 
upon them has not only been tested out thoroughly in 



60 Steam Engineering 

former boilers of this construction^ but has been tried in 
the boiler illustrated by means of hydraulic jacks and 
found to be entirely adequate. 

In this particular boiler the upper drum is 48 and the 
lower 40 inches in diameter^ with 11 rows of connecting 
3-inch tubes and; with 22 tubes in each row^ furnishing 
2,377 square feet of water-heating surface. The front and 
rear groups contain four rows each, the central group, three 
rows. 

The baffling is arranged to give three passes as shown, 
the gases passing longitudinally through each group of 
tubes. This gives a travel of the gas of something like 
40 feet in contact with the heating surface, yet with such 
freedom of passage that there was little drop in draft 
pressure between the stack and the furnace when the boiler, 
nominally rated at 238 horsepower, was developing over 
500, and burning 36.7 pounds of coal per square foot of 
grate. 

At each end of the upper drum is a dry chamber, as 
shown in the longitudinal section (Fig. 26), in which is 
placed a separator upon each end of the steam-outlet pipe, 
with the inlet facing toward the end of the drum and 
away from the steam-liberating surface. The boiler ap- 
pears to be one which will be well adapted to the large 
units and intensive service demanded by the modern power 
plant, especially those in which large amounts of power 
are required for peak periods arid where the ability to 
stand forcing is particularly desirable. 



Setting Return Tubular Boilers 61 

SETTING RETURN TUBULAR BOILERS. 

In setting a return tubular boiler the prevailing cus- 
tom has been to support on cast iron brackets resting upon 
the side walls^ which are liable in course of time to crum- 
ble away and cause trouble. A great improvement is made 
when we suspend such boilers from I-beams supported by 
cast iron columns. Figures 27 and 28 show the setting of 
this type of boilers either singly or in double batteries^ by 
means of suspension. In setting an even number of boil- 
ers^ as six or eight in one settings it is best to divide them 
into pairs so that not more than two boilers will be sus- 
pended between supports. 

The principal reason for this is that when the large sizes, 
such as from 150 to 250 horsepower, are used, the size 
I-beam required to safely carry this load between supports 
is so large that it overbalances the cost of two or more 
cast-iron columns. 

In setting an odd number of boilers, such as three or five, 
in a battery, columns are usually placed between the boilers 
with a 2-inch air space all around the column, and an air 
duct at the bottom of the setting which runs through from 
the front to the back and connects with, each air space 
around the column. This allows a free circulation of air, 
thus tending to keep the columns comparatively cool. In 
setting boilers in this way, the columns and I-beams are 
set in position first. The boiler is then hoisted to the proper 
height by means of tackle, which is attached to the I-beams, 
land when the boiler is brought to the proper height, the 
U-bolts are slipped into place and fastened by nuts and 
washers to the I-beams. 



62 



Steam Engineering 



This method abolishes the use of blocking and leaves all 
of the space under the boilers clear for the brick work. 




Fig. 27 



The expansion is easily taken care of by the U-bolts and 
hangers^ and if the walls are properly set, they will show 



Setting Return 'T^ubular Boilers 



63 



no cracks as the}^ carry no weighty and are free to go and 
come. The accompanying table^ No. 1, has been carefully 
worked out with a factor of safety of 5^ and gives the dif- 
ferent sizes and lengths of I-beams and columns required 




Fig. 28 



for boilers of 36 inches in diameter and 8 feet long, to 
boilers of 90 inches in diameter and 20 feet in length, giv- 
ing the total weight to be supported and the sizes, weights, 
land positions of the columns, and I-beams required : 



64 



Steam Engineering 



Table 1 

sizes and weights of columns and i-beams re 



HORSE POWER 
Dia. of boiler in inches 
Length of tuoes in feet 
Length of curtain sheet 

in inches , 

Total weight of boiler 

and water 

Rear head to center of 

hanger 

Center to cen. of hang'rs 
Front head to center of 

hanger , 

Distance between C of 

supports (1 boiler) , . 
Distance between C of 

supports (2 boilers) . . 
Length of I-beam for 

1 boiler 

Length of I-beam for 

2 boilers 

Size of I-beam required 

for 1 boiler 

Size of I-beam required 

for 2 boilers. . . , 
Weight per ft. of I-beam 

for 1 boiler. .... 
Weight per ft. of I-beam 

for 2 boilers 

Length of cast-iron col. 
Outside dia. of C. I. col. 

for 1 boiler. .... 
Outside dia. of C. I. col. 

for 2 boilers. . . . , 
Size of flange on ends of 

col. for 1 boiler. 
Size of flange on ends of 

col. for 2 boilers. 
Thickness of C. I. col. 

for 1 boiler 

Thickness of C. I. col. 

for 2 boilers. . . . 



15 
36 

8 


20 
36 
10 


25 
42 
10 


30 

42 
12 


35 
44 
12 


40 

48 
12 


45 
50 
13 


50 
54 
13 


11 
6500 


11 
7500 


12 

9400 


12 
10500 


12 
11500 


14 
13300 


14 
14200 


14 
15300 


2-0 
4-0 


2-6 

5-0 


2-6 
5-0 


3-0 

6-0 


3-0 
6-0 


3-0 
6-0 


3-3 

6-6 


3-3 
6-6 


2-0 


2-6 


2-6 


3-0 


3-0 


3-0 


3-3 


3-3 


6-6 


6-6 


7-0 


7-0 


7-2 


7-6 


7-8 


8-0 


11-8 


11-8 


12-8 


12-8 


13-0 


13-8 


14-0 


14-0 


. 7-3 
12-6 


7-3 
12-6 


7-10 
13-8 


7-10 
13-8 


8-0 
14-0 


8-4 
14-8 


8-6 
15-0 


8-10 
15-10 


4 


4 


5 


5 


5 


6 


6 


6 


C 


6 


8 


8 


9. 


^ 


9 


10 


7.5 


7.5 


9.75 


9.75 


9.75 


12.25 


12.25 


12.25 


12.25 

8-0 


12.25 

8-0 


18 
8-6 


18 
8-6 


21 

a-8 


21 
9-3 


21 
9-5 


25 
10-0 


4 


4 


4 


4 


4 


5 


5 


5 


5 


5 


5 


5 


5 


6 


6 


6 


n 


9J 


10 


10 


10 


lOJ 


lOi 


lOJ 


lOJ 


lOi 


12 


12 


12i 


12J 


12J 


13J 


I 


i 


I 


i 


I 


J 


I 


I 


I 


i 


1 


1 


i 


i 


I 


I 



60 
54 
15 

14 

17800 

3-0 
7-6 

3-9 

8-0 



8-10 
15-10 
6 
10 
12.25 

25 

10-0 



lOi 

13i 

I 

% 



Setting Return Tubular Boilers 



65 



Table 1 — continued, 
quired in setting return tubular boilers. 



70 
60 
14 

16 

20800 

3-6 
7-0 

3-6 

9-0 

16-2 

10-0 

17-4 

7 

12 

15 

31.5 

10-8 



111 

141 



75 
60 
15 


80 
60 
16 


90 
66 
15 


16 

24800 


16 

27200 


17 
30300 


3-9 

7-6 


4-0 

8-0 


3-9 

7-6 


3-9 


4-0 


3-9 


9-0 


9-0 


9-6 


16-2 


16-2 


17-2 


10-0 


10-0 


10-6 


17-4 


17-4 


18-4 


7 


7 


7 


12 


12 


12 


15 


15 


15 


31.5 

10-^8 


31.5 
10-8 


40 
11-2 


5 


5 


6 


6 


6 


6 


Hi 


m 


Hi 


14 


14 


14i 


s 


i 


i 


1 


3 

1 


1 



100 

66 
16 

17 
35000 



4-0 

8-0 

4-0 

9-6 

17-2 

10-6 

18-4 

7 

12 

15 

40 
11-2 

6 

6 

Hii 

14i| 



125 

72 
16 

18 

40000 



150 

72 

18 



18 
44000 



4-0| 4-6 



-0 

4-0 

10-0 

18-2 

11-0 

19-5 

8 

15 

18 

42 
12-0 



9-0 

4-6 

10-0 

18-2 

11-0 

19-5 

8 

15 

18' 

42 
12-0 



78 
18 

18 

48000 

4-6 
9-0 

4-6 



200 

7 
20 

18 
56000 



5^ 
10-0 



5-0 



10-61 10-6 
19-2 



19-2 
11-7 

20-B 



11-7 

20-6 
91 9 
15 
21 



"I 

211 



60 60 
12-6 12-6 



12i| 12i 

16J 16 

1 1 



200 
84 

18 

20 

55000 

4 
9-0 

4-6 

11-0 

20-2 

12-0 

21-6 

9 

15 

21 

60 
13-0 



12i 

16 

1 

1 



225 
84 
20 

20 
67000 



5-0 
10-0 

5-0 

11-0 

20-2 

12-0 

21-6 

9 

15 

21 

80 
13-0 



12i 

17 

1 

1 



225 
90 
18 

22 

65000 

4-6 
9-0 

4-6 

11-6 

21-2 

12-6 

22-6 

9 

15 

21 

80] 
13-10 



12i 

17 

1 

1 



250 

90^ 
. 20 

22 
75000 



5-0 
10-0 

5-0 

11-6 

21-2 

12-8 

22-6 

10 

15 

25 

80 
13-10 



13i 
17 

1 



66 Steam Engineering 

QUESTIONS AND ANSWERS. 

1. What types of boilers are most commonly trsed for 
stationary work ? 

Ans. The horizontal tnbnlar boiler and the water-tube 
boiler. 

2. Describe in general terms the horizontal tubular 
boiler. 

Ans, It consists of a shell having tubes of small diam- 
eter^ extending from head to head. 

These tubes are located in the water space. 

3. What is their function? 

Ans. To supply a passageway to the stack for the hot 
gases from the furnace. 

4. Does the water in the boiler receive heat from these 
tubes? 

Ans. It certainly does. 

5. Describe the route taken by the smoke and hot 
gases in the operation of a tubular boiler. 

Ans. From the furnace^ located under the front end 
of the boiler^ the gases pass under and along the sides of 
the shelly back to the rear end^ the upper part of which is 
arched over. The route is here reversed^ and the products 
of combustion return through the flues towards the front 
end and thence through the breeching into the stack. 

6. Is this type of boiler economical in the burning of 
fuel? 

Ans. It can be made so if properly set and handled in 
operation. 

7. Describe in a general way the water-tube boiler. 
Ans. It consists of a set^ or sets of tubes 3 to 4 inches 

in diameter, sometimes vertical, and sometimes inclined. 



Questions and Answers 67 

and connected at the top to a steam drum, and at the bot- 
tom to a mud drum. 

8. What advantages as regards circulation of the water 
has the water tube boiler ? 

Ans, It provides for a free circulation. 

9. Name another advantage connected with the water 
tube boiler. 

Ans, The margin of safety from dangerous explosions. 

10. Why is this ? 

Ans. Because if one or more tubes give way the pres- 
sure is relieved. 

11. What precautions should be observed in the design 
and construction of a boiler? . 

Ans. The best materials should be used, the boiler 
should be simple in design, and the workmanship should be 
perfect. 

12. Where should the mud drum be located? 

Ans. In a place removed from the action of the fire. 

13. What should be the capacity of the boiler relative 
I to its work? 

Ans. It should have a steam and water capacity suf- 
ificient to prevent any fluctuation in either the steam pres- 
sure, or the water level, if properly fed. 

14. Wliy should the water in a boiler circulate freely 
and constantly? 

Ans. In order to maintain all parts at as near the same 
temperature as possible. 

' ■ 15. What should the strength of a boiler be, relative to 
the strain it is liable to be subject to? 

Ans. It should have a great excess of strength. 

16. Is a combustion chamber an advantage to a boiler? 



68 Steam Engineering ' 

Ans. It is^ in order to complete the combustion of the 
gases before they escape to the chimney. 

17. How should a boiler be arranged with regard to 
cleaning ? 

Ans. All parts should be easily accessible for cleaning 
and repairs. 

18. What type of boiler is the Cahall? 
Ans. It is a water-tube boiler. 

19. Is it vertical or horizontal? 
Ans. It is built either way. 

20. What form of Cahall is generally used in central 
power stations ? 

Ans. The horizontal form. 

20a. What is the range of pressures that these boilers 
a/e built for? 

Ans. From 160 to 500 pounds per square inch. 

21. Describe the method of constructing the joints. 
Ans. The sheets are beveled on the edges^ bent into 

shape^ and rivet holes drilled after bending. 

22. What is gained by so doing? 

Ans. Absolutely round rivet holes and no crystalliza- 
tion. 

23. What type of riveted joint is used on the higher 
pressure boilers ? 

Ans. Triple riveted^ double strapped. 

24. How are the tubes connected to the steam drum 
in the Cahall boiler? 

Ans. By nipples connected to saddles on the drumo 

25. Does this boiler rest upon the brick work? 

Ans. It does not/ but is suspended free from the ma- 
sonry. 

26. What advantage is there in this style of setting? 



Questions and Answers 69 

Ans. The entire structure is free to expand or contract 
without causing any strains on either boiler or brick work. 

27. Describe the Heine boiler. 

Ans. It consists of one^ and sometimes two shells on 
drums resting upon water legs riveted to each end. These 
water legs are connected by horizontal tubes. The water 
fills the tubes^ water legs^ and partially fills the shell, leav- 
ing the upper portion for steam space. 

28. In the setting does this boiler occupy a horizontal 
position? 

Ans. No. The shell and tubes have an incline of one 
inch in twelve from front to rear. 

29. What provision is made for cleaning and repairing 
the tubes? 

A71S. Hand-holes are located in the head plates oppo- 
site each tube. 

30. How are these hand-holes closed? 
Ans, In the ordinary way^ by plates. 

31. Where is the mud drum located in the Heine boiler? 
Ans. Inside the shell, near the bottom. 

32. How is the Heine boiler supported in the setting? 
Ans. The front or fixed end rests upon cast iron col- 
umns. The rear water leg upon rollers. 

33. Describe in brief the Babcock & Wilcox boiler. 
Ans. It is composed of wrought iron tubes, placed in 

an inclined position, and connected with each other, and 
with a horizontal steam, and water drum by vertical headers. 

34. Where is the mud drum in this boiler ? 

Ans. In the rear, and connected to the lowest part of 
the boiler. 

35. What provision is made for cleaning the tubes in 
ithe Babcock & Wilcox boiler? 



70 Steam Engineering 

Ans. Through hand-holes in the headers, opposite each 
tube? 

36. How is this boiler supported in the setting? 
Ans. It is suspended from wrought iron girders, en- 
tirely independent of the brick work. 

37. Describe in general terms the Stirling boiler. 

Ans. It consists of three upper steam drums, each be- 
ing connected by a number of tubes to a lower or mud 
drum. 

38. How are the steam spaces connected? 
Ans. By shorter tubes. 

39. How is the boiler supported? 

Ans. On a structural steel frame work. 

40. What provision is made for expansion and contrac- 
tion of the tubes? 

Ans. They are slightly curved near the ends. 

41. How are the hot gases directed in their course 
from furnace to stack? 

Ans. By means of fire brick baffle walls. 

42. How is the interior of this boiler cleaned ? 

Ans. Pour manholes are provided in the drums, by 
which access to the interior of both the drums and tubes is 
obtained. 

43. What type of boiler is the Maxim boiler? 

Ans. It is a water- tube boiler consisting of two drums, 
one above the other, connected by tubes. 

44. Describe the tubes. 

Ans. Each tube has two bends, thus providing for un- 
equal expansion or contraction. 

45. How is the heating surface of the Maxim boiler 
arranged ? 



Questions and Answers 71 

Ans, It is so arranged that the current of heated gases 
is made to travel three times the length of the tubes^ the 
direction of the current being changed seven times in its 
route from furnace to stack. 

46. What can be said of the Bigelow-Hornsby water- 
tube boiler ? 

Ans. Owing to the flexible form of its construction it 
is possible to build it in very large units^ 2^000 horsepower 
and upwards. 

47. What peculiar feature makes this possible? 

Ans. Each section is independent of its neighbor, ex- 
cept the nipples connecting with the steam drum, and the 
equalizing nipples connecting the bottom drums of the 
rear sections. 

48. How is the boiler supported? 
Ans. Entirely from overhead beams. 

49. What percentage of the heating surface do the tubes 
of the front unit comprise? 

Ans. More than 12 per cent. 

50. Where is the feed water first admitted? 
Ans. Into the bottom drum of the rear unit. 

51. Describe the course of the feed water. 

Ans. The feed water is admitted into the bottom drum 
of the rear unit, and is advanced gradually from the coldest 
to the hottest portion of the boiler. 

52. How is the speed of the feed water up the rear unit 
regulated ? 

Ans. By the amount of steam generated, ample time 
being permitted for scale forming matter to be deposited 
in the bottom drum of this unit. 

53. Where does the liberation of steam take place? 
Ans. In the upper drum. 



72 Steam Engineering 

54. What can be said of this boiler regarding the utili- 
zation of the heat? 

Ans. It is baffled so that the products of combustion 
are carried uniformly over the heating surfaces in thin 
layers, the baffle plates serving to guide the gases through in 
substantially uniform passages. 

55. To what factor of safety is the Bigelow-Hornsby 
boiler built? 

Ans. Five for 200 pounds working pressure. 

56. Describe in brief the Wickes vertical water- tube 
boiler. 

Ans. It consists of two cylinders joined together end- 
ways by straight tubes, and erected in a vertical position. 

57. What can be said of the top cylinder? 

Ans. It is the longer, and is designated the steam drum. 

58. ^ What about the bottom cylinder ? 

Ans. It is the shorter, and is designated the mud drum. 
Both cylinders vary in dimensions as to diameter and 
length, according to the power required of the boiler. 

59. Where are the manholes of the Wickes boiler? 
Ans. One is placed in the convex head of the steam 

drum : there are also a number of hand-holes in this head. 
A manhole is also placed in the lower or mud drum, near 
the floor, thus permitting access to the top and bottom of 
the boiler. 

60. How are these tubes divided? 

Ans. By heavy fire-clay tile these tubes are divided into 
two compartments. Those tubes in the front compart- 
ment are called the ^^risers^^ and those in the rear the 
^^downcomers.^^ 

61. What can be said of the heat in its double passage? 



Questions and Answers 73 

Ans. It surrounds completely^ and closely the tubes in 
both compartments. 

62. Where is the water line in this boiler ? 

Ans. At a sufficient height in the steam drum to in- 
sure the complete submersion of all the tubes. 

63. How is the brick work setting of the Wickes water- 
tube boiler arranged? 

Ans. It is independent of the weight of the boiler^ and 
free to expand or contract, 

64. Describe briefly the design of the Atlas water-tube 
boiler. 

Ans. It consists mainly of three drums and two water 
legs extending crosswise^ while the tubes extend lengthwise. 

65. What is the original feature in the design of "the 
water legs? - , 

Ans. They are formed by the continuation of front 
and rear shell plates. 

QQ. What other valuable feature is claimed for this 
boiler ? 

Ans. After the steam leaves the vessels containing water 
it is passed through a series of superheating tubes^ and is 
superheated. 

67. Describe the course of the feed water. 

Ans. It is fed first into the purifier, whence it over- 
flows into the rear drum and down into the rear leg, thence 
through the inclined tubes to the front leg, thence up into 
the front drum, where the steam is liberated and carried 
through superheating tubes to the steam drum. 

^^. What are the facilities for cleaning the water tube? 
of this boiler? 

Ans. An individual hand-hole is located opposite each 
lend of each water tube. 



74 Steam Engineering 

69. How is the interior of each of the three cross drums 
reached? 

Ans, Through a large manhole in each end. 

70. Describe briefly the design and construction of 
the Marzolf water-tube boiler. 

Ans. It consists of three drums connected with each 
other in triangular form. Drum A directly over the fire 
is connected by tubes with drum B above it^ and with drum 
C in the rear and slightly below it. Drum C, which is the 
mud drum^ is also connected with drum B. The tubes are 
each slightly bent. The steam is collected in drum B^ which 
is maintained about one-third full of water. 

71. Describe in brief the action of the heat upon this 
boiler. 

Ans. It acts first upon the water in drum A over the 
furnace/ then by means of a baffle wall it is carried along 
the inclined tubes to drum B^ where it is deflected and car- 
ried down along other inclined tubes to drum C^ thence to 
the stack. 

71. How are the products of combustion caused to act 
upon the lower bank of tubes? 

Ans. By means of baffle walls located in the rear of 
the furnace. 

72. At what point in this boiler is the feed water ad- 
mitted ? 

Ans. At the lowest pointy viz.^ the mud drum. 

73. What are the principal advantages claimed for the 
Duplex water-tube boiler? 

Ans. Delivery of superheated steam; the removal of 
steam from the boiler at a point where there is no ebul- 
lition; the drums not exposed to the direct action of the 
fire. 



Questions and Anstvers 75 

74. Describe in brief the design of this boiler. 

Ans. Two npper steam drums connected by tubes^ a 
mud drum at the bottom and rear which is connected to 
the upper drums by headers and short nipples. The tubes 
are inclined 20 degrees to insure rapid and positive cir- 
culation. 

75. How is this boiler supported? 
Ans. Upon a heavy steel framework. 

76. What is the leading feature in connection with 
the Erie City w^ater-tube boiler? 

Alls. The three banks of tubes are practically vertical^ 
connected to upper^ and lower drums^ and spaced so that any 
one of them may be cut cut for repairs without interfering 
with the others. 

77. How do the products of combustion act upon this 
boiler ? 

Ans. The baffling is arranged to pass three times across 
the tubes^ and at each end of the upper drum is a dry 
chamxber. 

78. Describe in brief the best method of supporting 
horizontal tubular boilers. 

Ans. By means of hangers suspended from I beams^ 
supported by cast iron columns. This takes the weight off 
the side walls. 



I 



Boiler Construction 



As it is of the highest importance not only to the engineer 
in charge of the plants but also to his assistants^ and in 
fact to all persons whose business compels them to be in 
the vicinity of the boiler-room^ that there should be abso- 







A S 







Fig. 29 

lutely no doubt as to the safe construction of the boilers, 
and their ability to withstand the pressures under which 
they are operated^, the author has compiled the following 




Fig. 50 



by such eminent authorities as Dr. Thurston^, Prof. Wm. 
Kent, Dr. Peabody, D. K. Clark, Hutton and many other 
experts have been consulted, and the author has also added 
data regarding the construction and strength of boilers. 
The deductions and reports of tests and experiments made 

77 



78 



Steam Engineering 



the results of his own observations^ collected during an 
experience of thirty-five years as a practical engineer. 

When steel was first introduced as a material for boiler 
plate^ it was customary to demand a high tensile strength, 
70^000 to 74,000 pounds per square inch, but experience 
and practice demonstrated in course of time that it was 
much safer to use a material of lower tensile strength. It 
was found that with steel boiler plate of high tenacity there 
was great liability of its cracking, and also of certain 




Fig. 31 

changes occurring in its physical properties, brought about 
by the variations in temperature to which it was exposed. 
Consequently present-day specifications for steel boiler plate 
call for tensile strengths running from 55,000 to 66,000 
pounds, usually 60,000 pounds per square inch. Dr. Thurs- 
ton gives what he calls ^^good specifications'^ for boiler steel 
as follows: ^^Sheets to be of uniform thickness, smooth 
finish, and sheared closely to size ordered/' Tensile strength 
to be 60,000 pounds per square inch for fire box sheets and 
55,000 pounds per square inch for shell sheets. Working 



Boiler Construction 7^ 

test : a piece from each sheet to be heated to a dark cherry 
red^ plunged into water at 60° and bent double^ cold, under 
the hammer. Such piece to show no flaw after bending. 
The U. S. Board of Supervising Inspectors of Steam Ves- 
sels prescribes^ in Section 3 of General Eules and Eegula- 
tions, the following method for ascertaining the tensile 
strength of steel plate for boilers: *^^There shall be taken 
from each sheet to be used in shell or other parts of boiler 
which are subject to tensile strain, a test piece prepared in 
form according in figure 32. The straight part in center 
shall be 9 inches in length and 1 inch in width marked with 
light prick punch marks at distances 1 inch apart, as shown, 
spaced so as to give 8 inches in length. The sample must 
show, when tested, an elongation of at least 25 per cent in 
a length of 2 inches for thickness up to % inch, inclusive ; 
in a length of 4 inches for over i/4 i^^ch to -/g inches, in- 
clusive ; in a length of 6 inches, for all plates over ^q inches 
and under 1% inches in thickness. The samples shall also 
be capable of being bent to a curve of which the inner 
radius is not greater than II/2 times the thickness of the 
plates, after having been heated uniformly to a low cherry 
red and quenched in water of 82° F. 

Punched and Drilled Plates. Much has been written on 
this subject, and it is still open for discussion. If the 
material is a good, soft steel, punched sheets are apparently 
, as strong and in some instances stronger than drilled ; espe- 
cially is this the case with regard to the shearing resistance 
of the rivets, which is greater with punched than with drilled 
holes. 

Concerning rivets and rivet iron and steel. Dr. Thurston 
has this to say in his "Manual of Steam Boilers'' : "Eivet 
iron should have a tenacity in the bar approaching 60,000 



80 Steam Engineering 

pounds per square inch^ and should be as ductile as the very 
best boiler plate when cold. A good %-inch iron rivet can 
be doubled up and hammered together cold without ex- 
hibiting a trace of fracture/^ The shearing resistance of 
iron rivets is about 85 per cent and that of steel rivets 
about 77 per cent of the tenacity of the original bar^ as 
shown by experiments made by Greig and Eyth. The re- 
searches made by Wohler demonstrated that the shearing 
strength of iron was about four- fifths of the tensile strength. 

For the benefit of beginners^ the following simple rules 
are given for finding the percentage of efficiency, or in other 
words the ratio of the strength of the riveted joint, to the 
strength of the solid plate. In these calculations the tensile 
strength of the rivets was assumed to be 38^000 to 40,000 
pounds per square inch. The highest efficiency is attained 
in a riveted joint when the tensile strength of the rods from 
which the rivets are cut approaches that of the plates, and 
when the proportions of the joint are such that the tensile 
strength of the plates, the shearing strength of the rivets, 
and the crushing resistance of the rivets and plate, for a 
given section or unit strip, are as nearly equal as it is 
possible to secure them. 

The shell should be made of homogeneous steel of about 
60,000 pounds tensile strength. The thickness depending 
upon the pressure to be carried. The term tensile strength 
means that it would take a pull of 60,000 pounds in the 
direction of its length to break a bar of the material one 
inch square, or two inches wide by one-half inch thick, or 
three-eighths of an inch thick by 2.67 in. wide. 

The heads are generally made % iiich thicker than the 
shell. 



Boiler Construction 81 

Riveting. Boiler rivets should be of good charcoal iron, 
or a soft^ mild steel of 38^000 pounds to 40^000 pounds, T. S. 
No boiler is stronger than its weakest p art, and it is evident 
that a riveted joint has not the full strength of the solid 
plate. In order to ascertain the safe working pressure of a 
boiler it is necessar}^ to first determine the strength of the 
riveted seams, and the method of doing this is as follows : 
Assume the boiler to be of the horizontal tubular type, 60 
inches in diameter by 16 feet in length. The plates to be 
of steel % in. thick, having a tensile strength of 60,000 
pounds per square inch, the longitudinal seams to be double 
riveted and the girth seams to be single riveted. The pitch 
of the rivets, that is the distance from the center of one 
rivet hole to the center of the next one in the same row, to 
be for the double riveted seams 3i/4 inches and for the 
single riveted seams 2% inches. The diameter of the rivets 
to be ys inches and diameter of holes to be |-f inches. 
Assume the rivets to have a T. S. of 38,000 pounds per 
square inch of sectional area. First, find strength of a 
section of solid plate 3i/4 inches wide, which is the width 
between centers of rivet holes before punching. 

Rule 1 Pitch X thickness X T. S. Thus, 3.25 X .375 X 
60,000 = 73,125 pounds, strength of solid plate. 

Second, find strength of net section of plate, meaning 
that portion of plate left after deducting the diameter of 
,one hole ^f inches, which expressed in decimals = .9375 
inches from the width of plate before punching. 

Rule 2. Pitch— diameter of hole X thickness X T. S. 
Thus, 3.25— .9375X.375X60,000=52,031 pounds, strength 
of net section of plate. 

Third, find strength of rivets. In calculating the strength 
of rivets in a double riveted seam, the sectional area of two 



82 Steam Engineering 

rivets must be considered^ taking one-half the area of two 

rivets in the first row^ and the area of another rivet in the 

second row. The area of a %-inch rivet is .6013 inches, 

but when in position it is asrumed to fill the hole \% inches. 

Consequently, its area would then be .69 inches and its 

strength is found by Eule 3. 

Rule 3. Sectional areaXT. S. Thus, .69X38,000=26,- 

220 pounds, strength of one rivet, and multiplying by 2, 

as there are two rivets, the result is 26,220X2=52,440 

pounds, strength of rivets in the seam under dftnsideration. 

It thus appears that the plate is the weakest portion and 

the percentage of strength retained is found by multiplying 

52,031 by 100 and dividing by 73,125, the strength of solid 

1 ^ rn. 52,031X100 ^, , , 

platOo Thus, i^TTo^ = 71.1 per cent. 

The query might arise, why is the diameter of one rivet 
hole deducted from the pitch when figuring the strength 
of net plate? The answer is, that in punching the holes 
one-half the diameter of each hole is cut from the section 
designated, thereby reducing its width by just that amount. 

The 71.1 per cent obtained by the calcul«tion represents 
the strength of the boiler as compared to the strength of 
the sheet before punching, and should enter into all calcu- 
lations for the safe working pressure. 

It is usual in practice to figure the strength of a double- 
riveted seam at 70 per cent of the strength of the solid 
plate. The strength of triple-riveted butt joints may be 
calculated by taking a section of plate along the first row 
of rivets and estimate it as a single-riveted joint, then add 
to this result the strength of rivets in the second and third 
rows for a section of the same width. In properly designed 



Boiler Construction 83 

triple-riveted butt joints the percentage of strength retained 
is 88^ and some recent achievements in designing have 
shown the remarkable result of quadruple-riveted butt 
joints retaining as high as 92 to 94 per cent of the strength 
of the solid plate. 

Bursting Pressure. The query might arise^ why should 
the longitudinal or side seams require to be stronger than 
the girth or round about seams ? The answer is^ that the 
force tending to rupture the boiler along the line of the 
longitudinal seams is proportional to the diameter divided 
by two^ while the stress tending to pull it apart endwise is 
only one-half that^ or proportional to the diameter divided 
by four. 

To illustrate^ let Pig. 29 represent the shell of the boiler 
heretofore referred to^ ignoring for the time being the 
tubes and braces^ and consider the boiler simply as a hollow 
cylinder. Now the total force tending to rupture the boiler 
along the line of the girth seams or in the direction of the 
horizontal arrows=:area of one head in square inches X 
pressure in pounds per square inch. It is true that the 
pressure is exerted against both heads^ but the area of one 
head can only be considered for the reason that the two 
stresses are exerted against each other just as in the case o: 
•two horses pulling against each other^ or in opposite direc- 
tion on the same chain. The stress on the chain will h^ 
what one horse (not both) pulls. To further illustrate, 
suppose one of the horses to be replaced by a permanent 
post or wall and let one end of the chain be attached thereto. 
One head or one side of the boiler pulls against the other, 
and the stress on the seams is the force with which each 
(not both) pulls. Referring again to Fig. 29, area of one 
head=60^X. '^854=2827. 4 square inches. Suppose there is 



84 Steam Engineering 

a pressure of 10 pounds per square inch in the boiler. Then 
total stress on the girth seams=2827.4X 10=28,274 
pounds. Opposed to this pull is the entire circumference 
of the- boiler, which is 60X3.1416=188.5 inches. There- 
fore, dividing total pressure (28,274 pounds) by the cir- 
cumference in inches (188.5) will give 150 pounds as the 
stress on each inch of the girth seams. While the stress on 
each inch of the longitudinal seams or along the line A B, 
Fig. 29, and which is exerted in the direction of the vertical 
arrows, is pressure (10 pounds) X one-half the diameter 
(30 inches) =300 pounds. One-half the diameter is used 
because the pressure in any direction is effective only on 
the surface at right angles to that direction. 

The formula for finding the bursting pressure of a boiler 
may be expressed as follows : 

T S xT 

B= — -^ in which B=bursting pressure. 

T.S.=tensile strength. 
T=thickness of sheet. 
E==radius or one-half the diam. 
Example. T.S.= 55,000 pounds per square inch. 

T=% inches (expressed decimally=:.375 

inches). 
E=30 inches. 
Then 55,000X. 375-^30=687.5 pounds per square inch, 
which is the pressure at which rupture would take place 
provided there were no seams in the boiler and the original 
strength of the sheet was retained, but, as has been seen, a 
certain percentage of strength is lost through punching or 
drilling the necessary rivet holes, and this must be taken 
into account. 



Boiler Construction 85 

The formula now becomes^ for double riveting^ 

T.S.XTX-'^O 
g— -_i^ — — : — ^ {^ which the letters preserve the same 

value as in the original formula^ but the result is reduced 

by multiplying by the decimal .70, which represents the 

percentage of strength retained by double-riveted seams. 

n .1 T^ -11 5 5,QQ0X.375 X.70 ,^, . 

Consequently B will now= ^-r — =481 pounds. 

In case the seams are all single riveted ,56 must be sub- 
stituted for .70, and with triple-riveted butt joints .88 can 
safely be used. 

Safe Working Pressure. In order to ascertain the safe 
working pressure of a boiler it is necessary first to calcu- 
late the bursting pressure and divide this by another factor 
called the factor of safety. The one most commonly used 
for boilers is 5, or in other words the safe working pressure 
^ one-fifth the bursting pressure. In the case of the boiler 
under consideration, the safe pressure would be 481-^5=96 
pounds, at which point the safety valve should blow off. 

Bracing. Every engineer can easily ascertain for him- 
self whether the boilers under his charge are properly braced 
or not. The parts that require bracing are : all flat surfaces, 
such as the sides and top of the fire-box in boilers of the 
locomotive type, and those portions of the heads above and 
below the tubes in horizontal tubular boilers, also the top 
of the dome. 

The stress per square inch of sectional area on braces 
and stays should not exceed 6,000 pounds. It is customary 
to consider the flange of the head and the top row of tubes 
as sufficient bracing for a space two inches wide above the 



86 



Steam Engineering 



tubes and the same distance around the flange. Therefore 
the part of the head to be braced will be the segment con- 
tained within a line drawn two inches above the top row 
of tubes and two inches inside the flange. 

In order to ascertain the number of braces required for 
a given boiler head^ three factors are necessary : first, the 
area of the segment in square inches; second, the diameter 
and T. S. of the braces, and third, the pressure to be carried. 
By the use of Table 2 the areas of segments of boiler 
heads ranging from 42 to 72 inches in diameter can easily 
be obtained. Assume the boiler to be 60 inches in diame- 
ter, distance from top of tubes to top of shell 24 inches. 
Deduct 4 inches for surface braced by top row of tubes and 
flange, leaving the height of segment to be braced 20 inches. 

Table 2 



Diameter 


Distance from 


Height of 


Constant 


of Boiler. 


Tubes to Shell. 


Segment. 




42 in. 


15 in. 


11 in. 


.16314 


44 in. 


17 in. 


13 in. 


.1936 


48 in. 


19 in. 


15 in. 


.20923 


54 in. 


21 in. 


17 in. 


.21201 


60 in. 


24 in. 


20 in. 


.22886 


66 in. 


25 in. 


21 in. 


:214 


72 in. 


29 in. 


25 in. 


.24212 



Rule. Multiply the square of the diameter of the boiler 
by the constant number found in right hand column oppo- 
site column headed diameter. 

Example, 60X60X.^2886=823.89 square inches, area 
of segment to be braced. Find number of braces required. 
Assume the braces to be 1% inches in diameter and of a 
T. S. of 38,000 pounds per square inch of section. The 
area of one brace will be .994 square inches, whichX^^OOO 
pounds gives 5,964 pounds as the stress allowable on each 
brace. Suppose the pressure to be carried is 100 pounds 



Boiler Construction 87 

per square inch. There will be area of segment (823.89 
square inches) Xpi"essure (100 pounds) =82^389 pounds^ 
total stress. Dividing this result by 5^964 pounds (the 
capacity of each brace) gives 13.8 braces as the number 
needed. In practice there should be fourteen. 

Having a T. S. of 38,000 pounds and using 6 as the 
factor of safety^ each brace could safely sustain a pull of 
6^295 pounds. Therefore it is evident that the above men- 
tioned load for each brace is well within the limit. For 
convenience in calculating the areas of segments of circles^ 
other than those mentioned in Table 2^ the following rule 
is given : 

Eeferring to Figure 30 it is desired to find the area of 
the segment contained within the lines A B C E. It will 
be necessary first to find the area of the sector bounded by 
the lines A B C D. This is done by multiplying one-half 
the length of the arc^ A B C^ by the radius^ D B. Having 
obtained the area of the sector, the next step is to find the 
area of the triangle bounded by the lines A E C D and sub- 
tract it from the area of the sector. The remainder will 
be the area of the segment. Having found the area of the 
surface to be braced, and the number of braces required, 
it now becomes necessary to consider the spacing of the 
same. 

Rule. Divide area to be braced by the number of braces, 
and extract the square root of quotient. 

Example. 823.89-^14=58.8 square inches to be allotted 
to each brace. Extract square root of 58.8 and the result is 
7.68 inches, which is the length of one side of the square 
which each brace will be required to sustain. 

For internally fired boilers the same rules can be applied 
except that the surfaces to be braced are generally of rec- 



88 Steam Engineering 

tangiilar shape and consequently the area is more easily 
figured than in the case of segments. That part of the 
head below the tubes also requires to be braced^ and two 
braces are generally sufficient, as at A and B, Fig. 31. In 
the case of domes it is safe to consider the portion of the 
head within three inches of the flange as sufficiently braced. 
Then suppose the dome to be 36 inches in diameter, there 
will remain a circle 30 inches in diameter to be braced. 
The circumference of this circle is 94.2 inches and the 
pitch, or distance from center to center of the braces, being 
7.6 inches, the number of braces required is found by divid- 
ing 94.2 by 7.6, giving 12 braces. These braces should be 



\ Cj , /^ i 







*z 



Fig. 32 
test piece 

located along a line which is one-half the pitch, or 3.8 
inches, within the circumference of the 30-inch circle. The 
space immediately surrounding the hole cut for the steam 
outlet will be sufficiently re-enforced by the flange riveted 
on for the reception of the steam pipe. All holes cut in 
boilers, such as man holes, hand holes, and those for pipe 
connections, above two inches should be properly re-enforced 
by riveting either inside or outside a wrought-iron or steel 
ring or flange of such thickness and width as to contain at 
least as much material as has been cut from the hole. 

The preceding rules and calculations will serve to give 
the young student an idea of the need of mathematics in 



Boiler Construction 



89 



boiler makings and the subject is to be pursued still farther 
and deeper^ thus enabling the engineer in charge of a steam 
plant to calculate for himself whether or not his boilers are 
working within the margin of safety. 

The tables that follow have been compiled from the high- 
est authorities and show the results of a long and exhaustive 
series of tests and experiments made in order to ascertain 
the proportions of riveted joints that will give the highest 
efficiencies. 

The following Table 3 gives the diameters of rivets for 
various thicknesses of plates and is calculated according to 
a rule given by Unwin": 

Table 3 
diameters pf rivets. 



Thickness of 


Diameter of 


Thickness of 


Diameter of 


Plate. 


Rivet. 


Plate. 


Rivet. 


I in. 


i in 1 


1% in. 


i in. 


T¥ m. 


j\ m. 


^ in. 


if in. 


i in. 


H in. 


in. 


1^ in. 


f¥ in. 


3 in. 


in. 


11 in. 


J in. 


fl in. 


1 in. 


11 in. 



The efficiency of the joint is the percentage of the strength 
of the solid plate that is retained in the joints and it de- 
pends upon the kind of joint and method of construction. 

If the thickness of the plate is more than % inch^ the 
joint should always be of the double butt type. 

The diameters of rivets^ rivet holes^ pitch and efficiency 
of joints as given in the following Table 4^ which was pub- 
lished in the "Locomotive^^ several years ago^ were adopted 
at the time by some of the best establishments in the United 
States : 

Concerning the proportions of double-riveted butt joints. 
Prof. Kent says : ^Practically it may be said that we get 
a double-riveted butt joint of maximum strength by mak- 



90 



Steam Engineering 



ing the diameter of the rivet about 1.8 times the thickness 
of the plate, and making the pitch 4.1 times the diameter 
of the hole.^' 

Table 4 
proportions and efficiencies of riveted joints. 



Inch. 



Inch. Inch. Inch. Inch. 



Thickness of plate i 

Diameter of rivet i 

Diameter of rivet-hole \l 

Pitch for single riveting 2 

Pitch for double riveting 3 

Efficiency, single-riveted joint 66 

Efficiency, double-riveted joint 77 



15 


1 


/^ 


i 


16 


1 


\% 


i 


1 


H- 


I 


1^ 


2tV 


21 


2i% 


24 


31 


34 


31 


3^ 


.64 


.62 


.60 


.58 


.76 


.75 


.74 


.73 



Table 5 as given below is condensed from the report of a 
test of double-riveted lap and butt joints. In this test the 
tensile strength of the plates was 56^000 to 58^000 pounds 
per square inch, and the shearing resistance of the rivets 
(steel) was about 50,000 pounds per square inch. 

Table 5 
diameter and pitch of rivets— double-riveted joint. 



Kind of 
Joint. 


Thickness of 
Plate. 


Diameter of 
Rivet. 


Ratio of Pitch 
to Diameter. 


Lap 
Butt 
Butt 
Butt 


i inch 
i inch 
i inch 
1 inch 


0.8 inches 
0.7 inches 
1.1 inches 
1.3 inches 


3.6 inches 
3.9 inches 
4.0 inches 
3.9 inches 



Lloyd's ruleS;, condensed^ are as follows : 
Table 6 



LLOYD'S RULES— THICKNESS OF PLATE AND DIAMETER OF 

RIVETS. 



Thickness of 


Diameter of 


Thickness of 


Diameter of 


Plate. 


Rivets. 


Plate. 


Rivets. 


i inch 


i inch 


1 inch 


1 inch 


tV inch 


i inch 


^t inch 


i inch 


h inch 


i inch 


i inch 


1 inch 


1% inch 


1 inch 


Ts inch 


1 inch 


i inch 


1 inch 


1 inch 


1 inch 


U inch 


i inch 







Boiler Construction 91 

The following Table 7 is condiensed from one calculated 
by Prof. Kent^ in which he assumes the shearing strength 
of the rivets to be four-fifths of the tensile strength of the 
plate per square inch, and the excess strength of the per- 
forated plate to be 10 per cent. 

Table 7 

Pitch Efficiency 

Thickness Diameter Single Double Single Double 

of Plate. of Hole. Riveting. Riveting. Riveting. Riveting. 

Inches. Inches. Inches. Inches. Per Cent. Per Cent. 

i i 2.04 3.20 57.1 72.7 

>^^ 1 2.30 3.61 56.6 72.3 

h 1 2.14 3.28 53.3 70.0 

h II 2.57 4.01 56.2 72.0 

-^ff 1 2.01 --3.03 50.4 67.0 

1% II 2.41 3.69 53.3 69.5 

i^ff II 2.83 4.42 55.9 71.5 

i 1 1.91 2.82 47.7 64.6 

e II 2.28 3.43 50.7 . 67.3 

i n 2^67 4^10 .53.3 69.5 

Another table of joint efficiencies as given by Dr. Thurs- 
ton is as follows^ slightly condensed from the original cal- 
culation : 

Table 8 

Single riveting 

Plate thickness i^e" I" tV" i" I" 1" i" 1" 

Efficiency 55 .55 .53 .52 .48 .47 .45 .43 

Double riveting 

Plate thickness I" j\" I" I" I" 1" 

Efficiency 73 .72 .71 .66 .61 .63 

The author has been at considerable pains to compile 
Tables 9^ 10 and 11, giving proportions and efficiencies of 
single lap, double lap and butt, and triple-riveted butt joints. 
'The highest authorities have been consulted in the com- 
iputation of these tables and great care exercised in the cal- 
culations : 

It will be noticed that in single-riveted lap joints the 
highest efficiencies are attained when the diameter of the 



f 



92 Steam Engineering 

rivet hole is about 2 1/3 times the thickness of the plate^, 
and ^he pitch of the rivet 2% times the diameter of the 
hole. 

Table 9 
proportions of single-riveted lap joints. 



Thickness of 


Diameter of 


Pitch of Rivet, 


Efficiency, 


Plate, Ii 


iches. 


Rivet, Inches. 


Inches. 


Per Cent. 


1% 




i\ 




1.13 


50.5 


j^ 




i 




1.33 


53.3 


1% 




H 




1.55 


55.7 


i 








1.60 


53.3 


i 




1 




2.04 


57.1 






i 




1.87 


53.2 


JL. 




1 




2.30 


56.6 


1 




1 




2.14 


53.3 


i 




' 11 




2.57 


56.2 


1% 




1 




2.01 


50.4 






11 




2.41 


53.3 


^'l 




11 




2.83 


55.9 




11 




2.28 


50.7 


1 




11 




2.67 


53.3 



With the double-riveted joint it appears^ according to 
Table 10^ that in order to obtain the highest efficiency^ tbo 
joint should be designed so that the diameter of the rivet 
hole will be from 14/5 to 2 times the thickness of plate, 
and the pitch should be from 3 1/3 to 3% times the diam- 
eter of the hole. Concerning the thickness of plates Dr. 
Thurston has this to say: "Very thin plates cannot be 
well caulked^ and thick plates cannot be safely riveted. The 
limits are about 1/4 of an inch for the lower limit^, and % 
of an inch for the higher limit.^^ The riveting machine, 
however, overcomes the difficulty with very thick plates. 

The triple-riveted butt joint with two welts, one inside 
and one outside, has two rows of rivets in double shear and 
one outer row in single shear on each side of the butt, the 
pitch of rivets in the outer rows being twice the pitch of the 
inner rows. One of the welts is wide enough for the three 



Boiler Construction 93 

rows of rivets each side of the butt^ while the other welt 
takes in only the two close pitch rows. 

Table 10 
proportions of double-riveted lap and butt joints. 



Thickness 


of 


Diameter of 


Pitch of 


Efficiency, 


Plate, Inches. 


Rivet 


, Inches. 


Rivet, Inches. 


Per Cent. 


j% 






1% 


1.71 


67.1 


li 








2.05 


69.5 


i 








2.46 


69.5 


i 








3.20 


72.7 


tV 






I 


2.21 


66.2 








\ 


2.86 


69.4 


tV 






1 


3.61 


72.3 


^ 






1 


3.28 


70.0 


i 






11 


4.01 


72.0 


T% 






1 


3.03 


67.0 


J% 






11 


3.69 


69.5 


iV 






11 


4.42 


7L5 


i 






11 


3.43 


67.3 








n 


4.10 


69.5 








1 


2.50 


72.0 








11 


3.94 


74.2 


1 






11 


4.10 


76.1 



When properly designed this form of joint has a high 
efficiency, and is to be relied upon. Table 11 gives propor- 
tions and efficiencies, and it will be noted that the highest 
degree of efficiency is shown when the diameter of rivet 
hole is from 1^/4 to 1^/2 times the thickness of plate, and 
the pitch of the rivets is from 3^/2 to 4 times the diameter 
' of the hole. This, of course, refers to the pitch of the close 
rows of rivets, and not the two outer rows. 

The highest efficiency is attained in a riveted joint when 
the tensile strength of the rods from which the rivets are 
cut approaches that of the plates, and when the propor- 
tions of the joint are such that the tensile strength of the 
plates, the shearing strength of the rivets, and the crushing 
resistance of the rivets and plate, for a given section or 
unit strip, are as nearly equal as it is possible to secure 
them. 



94 



Steam Engineering 



Table 11 

proportions of triple-riveted butt joints with in- 
side and outside welt. 



Thickness of 


Diameter of 


Pitch of 


Pitch of Outer 


Efficiency, 


Plate, Inches. 


Rivet, Inches. 


Rivet, Inches. 


Rows, Inches. 


Per Cent. 


1 


if 


3.25 


6.5 


84 


/f 


tI 


3.25 


6.5 


85 


i 


^1 


3.25 


6.5 


83 


t'^ 


3.50 


7.0 


84 


i 


1 


3.50 


7.0 


86 


i 


ItV 


3.50 


7.0 


85 


i 


IS 


3.75 


7.5 


86 


1 


11 


3.87 


7.7 


84 



A few examples of calculations for efficiency will be 
given, taking the three forms of riveted joints in most com- 
mon use. The following notation will be used throughout : 
T. S.=Tensile strength of plate per square inch. 

T=Thickness of plate. 

C= Crushing resistance of plate and rivets. 

A= Sectional area of rivets. 

S^ Shearing strength of rivets. 

D=Diameter of hole (also diameter of rivets when 
driven). 

P=Pitch of rivets. 

In the calculations that follow T. S. will be assumed to 
be 60,000 pounds, S will be taken at 45,000 pounds, and 
the value of C may be assumed to be 90,000 to 95,000. 

DOUBLE-RIVETED LAP AND BUTT JOINTS. 

Figure 33 shows a double-riveted lap joint. The style of p 
riveting in this joint is what is known as chain riveting. 

In case the rivets are staggered, the same rules for cal- 
culating the efficiency will hold as with chain riveting, for 
the reason that with either style of riveting the unit strip 
of plate has a width equal to the pitch or distance p. (Fig. 
33.) 



rt: 



Boiler Construction 



95 



The dimensions of the joint under consideration are as 
follows: Pi=:3^ inches^ T^jV inch, D=:l inch (which 
is also diameter of driven rivet). 




Fig. 33 
double riveted lap joint 



The strength of the unit strip of solid plate is PXTX 
T. S.=85,312. 

The strength of net section of plate after drilling is 
IP— DXTXT.S.=59,062. 

The shearing resistance of two rivets is 2AXS=70,686. 

The crushing resistance of rivets and plate is DX^XT 
(XCi=i78,750. 

i It thus appears that the weakest part of the joint is the 
net strip or section of plate^, the strength of which is 59^062 
and the efficiency=59,062Xl00^85,312=z69.2 per cent. 

A double-riveted butt joint is illustrated by Fig. 34, and 
the dimensions are as follows : 

P, inner row of rivets==234 inches. 

P', outer row of rivets =5^/2 inches. 

T of plate and butt straps=: y'^e inch. 
: D of hole and driven rivet=l inch. 
; Failure may occur in this joint in five distinct ways, 
which will be taken up in their order. 



96 



Steam Engineering 



1. Tearing of the plate at the outer row of rivets. The 
net strength at this point is P— DXTXT.S., which, ex- 
pressed in plain figures, results as follows: 5.5 — 1X.4:375 
X60,000=118,125. 




Fig. 34 
double riveted butt joint 



2. Shearing two rivets in double shear and one in singly 
shear. Should this occur, the two rivets in the inner row 
would be sheared on both sides of the plate, thus being in 
double shear. Opposed to this strain there are four sec- 
tions of rivets, two for each rivet. Then at the outer row 
of rivets in the unit strip there is the area of one rivet in 
single shear to be added. The total resistance, therefore, 
is 5AXS as follows: .7854X5X45,000=176,715. 

3. The plate may tear at the inner row of rivets and 
shear one rivet in the outer row. The resistance in thia 
case would be P'— 2DXTXT.S.+AXS as follows: 5.5 
—2X.4375X60,000+. 7854X45,000=127,218. 

4. Failure may occur by crushing in front of three 
rivets. Opposed to this is 3DXTXC, or 1X3X.4375 
X95,000=124,687. 



Boiler Construction 



97 



5. Failure may occur by crushing in front of two rivets 
and shearing one. The resistance is represented by 2D XT 
XC+IAXS; expressed in figures, 1X^X.4375X95,000+ 
.7854X45,000=118,468. 

The strength of a solid strip of plate 51/^ inches wide 
before drilling is P'XTXT.S., or 5.5X.4375X60,000= 
144,375, and the efficiency of the joint is 118,125X100^ 
144,375=81.1 per cent. 



TRIPLE-RIVETED BUTT JOINT. 

A triple-riveted butt joint is shown in Pig. 35, the dimen- 
sions of which are as follows : 

T=iV inch, D=^f inch, A=.69 inch, P=33/g inches, 
P'=63^ inches. 

r- 




Fig. 35 
triple riveted butt joint 

Failure may occur in this joint in either one of five ways. 

1. By tearing the plate at the outer row of rivets where 
the pitch is 6% inches. The net strength of the unit strip 
at this point is P'— DXTXT.S., found as follows: 6.75— 
.9375X.4375X60,000=152,578. 



98 * Steam Engineering 

2. By shearing four rivets in double shear and one in 
single shear. In this instance^ of the four rivets in double 
shear^ each one presents two sections^ and the one in single 
shear presents one, thus making a total of nine sections of 
rivets to be sheared, and the strength is 9AXS, or .69 X 
9X45,000=279,450. 

3. Eupture of the plate at the middle row of rivets and 
shearing one rivet. Opposed to this strain the strength is 
P'— 2DXTXT.S.+1AXS, equivalent to 6.75— (.9375X 
2)X.4375X60,000+.69X90,000=190,068. 

4. Crushing in front of four rivets and shearing one 
rivet. The resistance in this instance is 4DXTXC+1AX 
S, or .9375X4X.4375X90,000+.69X4:5,000=:178,706. 

5. Failure may be caused by crushing in front of five 
rivets, four of which pass through both the inside and out- 
side butt straps, while the fifth rivet passes through the in- 
side strap only, and the resistance is 5DXTXC, equivalent 
to .9375X5X90,000=184,570. 

The strength of the unit strip of plate before drilling is 
P'XTXT.S., or 6.75X.4:375X60,000=177,187, and the 
efficiency is 152,578X100^177,187=86 per cent. 

With the constantly increasing demand for higher steam 
pressures, the necessity for higher efficiencies in tl^e riveted 
joints of boilers becomes more apparent, and of late years 
quadruple and even quintuple-riveted butt joints have in 
many instances come into use. The quadruple butt joint 
when properly designed shows a high efficiency, in some 
cases as high as 94.6 per cent. Figure 36 illustrates a joint 
of this kind, and the dimensions are as follows: 

T=y2 inch. 

D=tf inch. 

A=.69 inch. 



1 
Iff 



Boiler Construction 



99 



P, inner rows=3% inches. 

P'^ 1st onter row= 7% inches. 

V, 2d outer row=15 inches. 

The two inner rows of rivets extend through the main 
plate and both the inside and outside cover plates or butt 
straps. 



9&>, 




1 ^ 

liri 
m 



i % 
i \ 



SfTf 



% 






Fig. 36 
quadruple riveted butt joint 



The two outer rows reach through the main plate and 
inside cover plate only, the first outer row having twice 
the pitch of the inner rows, and the second outer row has 
twice the pitch of the first. 

Taking a strip or section of. plate 15 inches wide (pitch 
of outer row), there are four ways in which this joint may 
fail. 



100 steam Engineering 

1. By tearing of the plate at the outer row of rivets. 
The resistance is P"— DXTXT.S., or 15— .9375X.5X 
60,000=421,875. 

2. By shearing eight rivets in double shear and three 
in single shear. The strength in resistance is 19AXS, or 
.69X19X45,000=589,950. 

3. By learing at inner rows of rivets and shearing three 
rivets. The resistance is P"— 4DXTXT.S.+3AXS, or 
15— (.9375X4) X.5X60,000+.69X3X45,000=430,650. 

4. By tearing at the first outer row of rivets, where the 
pitch is 7% inches, and shearing one rivet. The resistance 
is P"— 2DXTXT.S.+AXS, or 15— (.9375X2) X.5 
X60,000+. 69X45,000=424,800. 

It appears that the weakest part of the joint is at the 
outer TOW of rivets, where the net strength is 421,875. The 
strength of the solid strip of plate 15 inches wide before 
drilling is P^XTXT.S., or 15X. 5X60,000=450,000, and 
the efficiency is 421,875X100^450,000=93:7 per cent. 

Figure 37 shows another style of quadruple-riveted butt 
joint. This joint is now used on nearly all high-grade 
boilers of the horizontal return-tubular type, and it marks 
about the practical limit of efficiency for riveted joints con- 
necting plates of uniform thickness together. The methods 
of failure to be considered are practically the same as in the 
two preceding joints, except that there are more rivets 
concerned in the calculations : 

(1) Pulling apart of the sheets along net section A A. 

(2) Pulling apart of the sheet along section D E F G 
and shearing rivets A, B, C. 

(3) Pulling apart of sheet along section D E F G and 
crushing of rivets A, B, C in the strap. 



Boiler Construction 



101 



(4) Shearing rivets A, B, C in single shear and D, E, 
P, G^ H, I, J^ K iu double shear. 

(5) Crushing of rivets D, E, F, G, H, I, J, K in plate 
and A, B^, C in the strap. 




© ! © © Q ©il , 
©__©__©_©__©__§jj 




Fig. 37 

QUADRUPLE RIVETED BUTT JOINT 



(6) Crushing of rivets D, E, F, G, H, I, J, K in the 
plate and shearing rivets A, B, C. 

Using the numerical values previously given : 

(1) (15.5— 1)X0.5625X55,000=448,580 pounds. 



102 Steam Engineering 

(2) [ (15.5— 4)X0.5625X55,000] + (3X42,000X 
0.7854) =454,739 pounds. 

(3) [ (15.5— 4)X0.5625X55,000] + (3X0.4375X1 
X95,000) =480,465 pounds. 

(4) (3X42,000X0.7854) + (8X^8,000X0.7854) = 
589,050 pounds. 

(5) (8X0.5625X1X95,000) + (3X0.4375X1X95,- 
000) =552,187 pounds. 

(6) (8X0.5625X1X95,000) + (3X42,000X0.7854) = 
536,461 pounds. 

The strength of the solid plate is 

15.5X0.5625X55,000=479,528 
pounds, and the failure of the sheet by pulling apart along 
the net section A A is the one that determines the efficiency 
of the joint, which is 

' -^93.55 per cent, 



479,528 



Staying Flat Surfaces, The proper staying or bracing 
of all flat surfaces in steam boilers is a highly important 
problem, and while there are various methods of bracing 
resorted to, still, as Dr. Peabody says, ^^the staying of a flat 
surface consists essentially in holding it against pressure at 
a series of isolated points which are arranged in regular or 
symmetrical pattern.^^ The cylindrical shell of a' boiler 
does not need bracing, for the very simple reason that the 
internal pressure tends to keep it cylindrical. On the con- 
trary, the internal pressure has a constant tendency to bulge 
out the flat surface. Eule 2, Section 6, of the rules of the 
TJ. S. Supervising Inspectors provides as follows: ^^No 
braces or stays hereafter to be employed in the construction 



Boiler Construction 103 

of boilers shall be allowed a greater strain than 6,000 
pounds per square inch of section/^ 

The method to be employed in staying a boiler depends 
upon the type of boiler and the pressure to be carried. For- 
merly when comparatively low pressures were used (60 to 
75 pounds per square inch) the diagonal crow foot brace 
was considered amply sufficient for staying the flat heads of 
boilers of the cylindrical tubular type, both above and be- 
low the tubes, but in the present age, when much higher 
pressures are demanded, through stay rods are largely 
employed. These are soft steel or iron rods li/4 to 2 inches 
in diameter^ extending through from head to head, with a 




Fig. 38 

pull at right angles to the plate, thus having a great advan- 
tage over the diagonal «tay in that the pull on the diagonal 
) stay per square inch of section is more than 5 per cent in 
' excess of what a through stay would have to resist under 
^ the same conditions of pressure. 

The weakest portion of the crow foot brace when in 

position is at the foot end, where it is connected to the 

'head by two rivets. With a correctly designed brace the 

I pull on these rivets is direct, and the tensile strength of the 

'i material needs to be considered only, but if the form of the 

'brace is such as to bring the rivet holes above or below the 

center line of the brace, or if the rivets are pitched too far 

from the body of the brace, there will be a certain leverage 



104 



Steam Engineering 



exerted upon the rivets in addition to tne direct pull. 
Figure 38 shows a brace of incorrect design and Figs, 39 
and 4Q show braces designed along correct lines. 




¥=---:.=yji 




Fig. 39 



lrg% ) 



Fig. 40 

Other methods of staying, besides the crow foot brace and 
through stays, consist of gusset stays, and for locomotives, 
and other fire box boilers screwed stay bolts are employed 
to tie the fire box to the external shell. The holes for these 
stay bolts are punched or drilled before the fire box is put 
in place. After it is in and riveted along the lower edge to 
the foundation ring, or mud ring as it is sometimes called, 
a continuous thread is tapped in the holes in both the out- 
side plate and the fire sheet by running a long tap through 
both plates. The steel stay bolt is then screwed through 
the plates and allowed to project enough at each end to 
permit of its being riveted cold. Stay bolts are liable to 
be broken by the unequal expansion of the fire box and 
outer shell, and a small hole should be drilled in the center 
of the bolt, from the outer end nearly through to the inner 
end. Then in case a bolt breaks, steam or water will blow 
out through the small hole, and the break will be discovered 



105 




Fig. 41 



IOC 



steam Engineering 



at once. The problem of properly staying the flat crown 
sheet of a horizontal fire box boiler^ especially a locomotive 
boiler, is a very difficult one and has taxed the inventive 
genius of some of the most eminent engineers. 

Before the invention of the Belpaire boiler, with its out- 
side, or shell plate flat above the fire box, the only method 



'm7T^71 




End Oevotipn, 
'SAornngAnochinent of ^003. Stays. 



Half Section C-a i ofSmoke-eou 



tialf End Elevation 



Fig. 42 



of staying the crown sheet was by the use of cumbersome 
crown bars or double girders extending across the top of 
the crown sheet, and supported at the ends by special cast- 
ings that rest on the edges of the side sheets and on the 
flange of the crown sheet. At intervals of 4 or 5 inches 
crown bolts are placed, haying the head inside the fire box 
and the nut bearing on a plate on top of the girder. There 



Boiler Construction 107 

is also a thimble for each bolt to pass through^ between the 
top of the crown sheet and the girder. These thimbles 
maintain the proper distance between the crown sheet and 
girder and allow the- water to circulate freely. 

The Belpaire fire box dispenses with girders, and permits 
the use of through stays from the top of the flat outside 
plate, through the crown sheet and secured at each end by 
nuts, and copper washers. 

For simplicity of construction and great strength the 
cylindrical form of fire box known as the Morison corru- 
gated furnace has proved to be very successful. This form 
of fire box was in 1899 applied to a locomotive by Mr. 
Cornelius Vanderbilt, at the time assistant superintendent 
of motive power of the New York Central & Hudson Eiver 
E. E. This furnace was rolled of %-inch steel, is 59 inches 
internal diameter and 11 feet 2^4 inches in length. It 
was tested under an external pressure of 500 pounds per 
square inch before being placed in the boiler. It is carried 
at the front end by a row of radial sling stays from the out- 
side plate, and supported at the rear by the back head. 
Figures 41 and 42 show respectively a sectional view, and 
an end elevation of this boiler. It will be seen at once that 
the question of stays for a fire box of this type becomes 
very simple. The boiler has proved to be so satisfactory 
that the company has since had many more of the same type 
constructed. 

Gusset stays are used mainly in boilers of the Lancashire 
model, and are triangular-shaped plates sheared to the 
proper form and having two angle irons riveted to the 
edges that comes against the shell, and the head. The angle 
irons are then riveted to the shell and the flat head. This 
form of brace is simple and solid, but its chief defect is, 



108 



Steam Engineering 



that it is very rigid, and does not allow for the iineq-Qal ex- 
pansion of the internal furnace flues and the shell. Fig. 43 
illustrates a gusset stay and the method of applying it. 




Fig. 43 



Coming now to through stay rods, it is safe to say that 
whenever, and wherever it is possible to apply them they 
should be used. In all cases they should be placed far 
enough apart to allow a man to pass between them for the 
purposes of inspection and washing out of the boiler. 
Through stay rods are usually spaced 14 inches apart hori- 
zontally, and about the same distance vertically. The ends, 
as far back as the threads run, are swaged larger than the 
body, so that the diameter at the bottom of the thread is 
greater than the diameter of the body. There are several 
methods of applying through stays. One of the most com- 
mon, especially for land boilers, is to allow the ends of the 
rod to project through the plates to be stayed, and holding 
them in place by a nut and copper washer, both inside and 
outside the plate. Another and still better plan is to rivet 
6-inch channel bars across the head, inside above the tubes, 
the number of bars depending upon the height of the seg- 
ment to be stayed. 

The channel bars are drilled to correspond with the holes 
that are drilled in the plate to receive the stay rods, which 
latter are then secured by inside and outside nuts and cop- 



Boiler Construction 



109 



per washers. These channel bars act as girders^, and serve 
to greatly strengthen the head or flat plate. Fig. 44 will 
serve to illustrate this method. 




Fig. 44 




Fig. 45 



Sometimes a combination of channel bar and diagonal 
crow foot braces is used, as shown by Fig. 45. 



110 steam Engineering 

A good form of diagonal crow foot stay is obtained by 
using double crow feet, made of pieces of boiler plate bent 
as shown by Fig. 46 and riveted to the plate by four rivets. 




Fig. 46 



A hole is drilled through the body of the crow foot, and 
a bolt passing through this secures the forked end of the 
stay. 




Fig. 47 



Another method of securing through stays to the heads 
is shown by Pig. 47 and is applied where too many stay 
rods would be required to connect all the points to be 



Boiler Construction 111 

stayed. A tie iron is first riveted to the flat plate to be 
stayed, and two V-shaped forgings are bolted to it as 
shown. The through stay is then bolted to the forgings, 
and thus two points in the flat head are supported by one 
stay. It will readily be seen that this method will reduce 
the number of through stay rods required. 

Calculating the Strength of Stayed Surfaces. In calcu- 
lations for ascertaining the strength of stayed surfaces, or 
for finding the number of stays required for any given flat 
surface in a boiler, the working pressure being known, it 
must be remembered that each stay is subjected to the pres- 
sure on an area bounded by lines drawn midway between 
it and its neighbors. Therefore the area in square inches, 
of the surface to be supported by each stay, equals the square 
of the pitch or distance in inches between centers of the 
points of connection of the stays to the flat plate. Thus, 
suppose the stays in a certain boiler are spaced 8 inches 
apart, the area sustained by each stay=8X8=64 square 
inches, or assume the stay bolts in a locomotive fire box to 
be pitched 4^/2 inches each way, the area supported by each 
stay bolt=4%X4:%=:20i4 square inches. Again taking 
through stay rods, suppose, for example, the through stays 
shown in Fig. 44 to be spaced 15 inches horizontally and 
14 inches vertically, the area supported by each stay=15 
X 14=210 square inches. 

The minimum factor of safety for stays, stay bolts and 
braces is 8, and this factor should enter into all computa- 
tions of the strength of stayed surfaces. 

The pitch for stays depends upon the thickness of the 
plate to be supported, and the maximum pressure to be 
carried. 



112 Steam Engineering 

In computing the total area of the sta3)'ed surf acef it is 
safe to assume that the flange of the plate, where it is 
riveted to the shell, sufficiently strengthens the plate for a 
distance of 2 inches from the shell, also that the tubes act 
as stays for a space of 2 inches above the top row. There- 
fore the area of that portion of the flat head or plate 
bounded by an imaginary line drawn at a distance of 2 
inches from the shell and the same distance from the last 
row of tubes is the area to be stayed. This surface may be 
in the form of a segment of a circle, as with a horizontal 
cylindrical boiler, or it may be rectangular in shape, as in 
the case of a locomotive, or other flre box boiler. Other 
forms of stayed surfaces are often encountered, but in gen- 
eral the rules applicable to segments or rectangular figures 
will suffice for ascertaining the areas. 

The method of finding the area of the segmental portion 
of the head above the tubes is as follows, using Table 12. 
The diameter of the circle and the rise or height of the 
segment being known, the area of the segment may be found 
by the following rule: 

Rule, Divide the height of the segment by the diameter 
of the circle. Then find the decimal opposite this ratio in 
the column headed "Area.^^ Multiply this area by the 
square of the diameter. The result is the required area. 

Example. Diameter of circle=72 inches. Height of 
segment=25 inches. 25-f-72=.347, which will be found 
in the column headed ^^Eatio,^^ and the area opposite this 
is .24212. Then .24212X'^^X'^^— 1,^55 square inches, 
area of segment. 



Boiler Construction 



113 



The following examples of calculating the number of 
braces, and the spacing of the same will serve to make the 
matter plain. 

A boiler is 66 inches in diameter, the working pressure 
is 100 pounds per square inch. The distance from the top 
row of tubes to the shell is 25 inches. Eequired, the num- 



Table 12 

AREAS OF SEGMENTS OF A CIRCLE. 



Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


.2 


.11182 


.243 


.14751 


.286 


.18542 


.329 


.22509 


.201 


.11262 


.244 


.14837 ' 


.287 


.18633 


.33 


.22603 


.202 


.11343 


.245 


.14923 


.288 


.18723 


.331 


.22697 


.203 


.11423 


.246 


.15009 


.289 


.18814 


.332 


.22792 


.204 


.11504 


.247 


.15095 


.29 


.18905 


.333 


.22886 


.205 


.11584 


.248 


.15182 


.291 


.18996 


.334 


.22980 


.206 


.11665 


.249 


.15268 


.292 


.19086 


.335 


.23074 


.207 


.11746 


.25 


.15355 


.293 


.19177 


.336 


.23169 


.208 


.11827 


.251 


.15441 


.294 


.19268 


.337 


.23263 


.209 


.11908 


.252 


.15528 


.295 


.19360 


.338 


.23358 


.21 


.11990 


.253 


.15615 


.296 


.19451 


.339 


.23453 


.211 


.12071 


.254 


.15702 


.297 


.19542 


.34 


.23547 


.212 


.12153 


.255 


.15789 


.298 


.19634 


.341 


.23642 


.213 


.12235 


.256 


.15876 


.299 


.19725 


.342 


.23737 


.214 


.12317 


.257 


.15964 


.3 


.19817 


.343 


.23832 


.215 


.12399 


.258 


.16051 


.301 


.19908 


.344 


.23927 


.216 


.12481 


.259 


.16139 


.302 


.20000 


.345 


.24022 


.217 


.12563 


.26 


.16226 


.303 


.20092 


.346 


.24117 


.218 


.12646 


.261 


.16314 


.304 


.20184 


.347 


.24212 


.219 


.12729 


.262 


.16402 


:305 


.20276 


.348 


.24307 


.22 


.12811 


.263 


.16490 


.306 


.20368 


.349 


.24403 


.221 


.12894 


.264 


.16578 


.307 


.20460 


.35 


.24498 


.222 


.12977 


.265 


.16666 


.308 


.20553 


.351 


.24593 


.223 


.13060 


.266 


.16755 


.309 


.20645 


.352 


.24689 


.224 


.13144 


.267 


.16843 


.31 


.20738 


.353 


.24784 


.225 


.13227 


.268 


.16932 


.311 


.20830 


.354 


.24880 


.226 


.13311 


.269 


.17020 


.312 


.20923 


.355 


.24976 


.227 


.13395 


.27 


.17109 


.313 


.21015 


.356 


.25071 


.228 


.13478 


.271 


.17198 


.314 


.21108 


.357 


.25167 


.229 


.13562 


.272 


.17287 


.315 


.21201 


.358 


.25263 


.23 


.13646 


.273 


.17376 


.316 


.21294 


.359 


.25359 


.231 


.13731 


.274 


.17465 


.317 


.21387 


.36 


.25455 


.232 


.13815 


.275 


.17554 


.318 


.21480 


.361 


.25551 


.233 


.13900 


.276 


.17644 


.319 


.21573 


.362 


.25647 


.234 


.13984 


.277 


.17733 


.32 


.21667 


.363 


.25743 


.235 


.14069 


.278 


.17823 


.321 


.21760 


.364 


.25839 


.236 


.14154 


.279 


.17912 


.322 


.21853 


.365 


.25936 


.237 


.14239 


.280 


.18002 


.323 


.21947 


.366 


.26032 


.238 


.14324 


.281 


.18092 


.324 


.22040 


.367 


.26128 


.239 


.14409 


.282 


.18182 


.325 


.22134 


.368 


.26225 


.24 


.14494 


.283 


.18272 


.326 


.22228 


.369 


.26321 


.241 


.14580 


.284 


.18362 


.327 


.22322 


.37 


.26418 


.242 


.14666 


' .285 


.18452 


.328 


.22415 


.371 


.26514 



114 



Steam Engineering 
•Table 12 — continTjed. 



Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


Ratio 


Area 


.372 


.26611 


.405 


.29827 


.438 


.33086 


.471 


.36373 


.373 


.26708 


.406 


.29926 


.439 


.33185 


.472 


.36471 


.374 


.26805 


.407 


.30024 


.44 


.33284 


.473 


.36571 


.375 


.26901 


.408 


.30122 


.441 


.33384 


.474 


.36671 


.376 


.26998 


.409 


.30220 


.442 


.33483 


.475 


.36771 


.377 


.27095 


.41 


.30319 


.443 


.33582 


.476 


.36871 


.378 


.27192 


.411 


.30417 


.444 


.33682 


.477 


.36971 


.379 


.27289 


.412 


.30516 


.-445 


.33781 


.478 


.37071 


.38 


.27386 


.413 


.30614 


.446 


.33880 


.479 


.37171 


.381 


.27483 


.414 


.30712 


.447 


.33980 


.48 


.37270 


.382 


.27580 


.415 


.30811 


.448 


.34079 


.481 


.37370 


.383 


.27678 


.416 


.30910 


.449 


.341V9 


.482 


.37470 


.384 


.27775 


.417 


.31008 


.45 


.34278 


.483 


.37570 


.385 


.27872 


.418 


.31107 


.451 


.34378 


.484 


.37670 


.386 


.27969 


.419 


.31205 


.452 


.34477 


.485 


.37770 


.387 


.28067 


[ .42 


.31304 


.453 


.34577 


.486 


.37870 


.388 


.28164 


.421 


.31403 


.454 


.34676 


.487 


.37970 


.389 


.28262 


.422 


.31502 


.455 


.34776 


.488 


.38070 


.39 


.28359 


.4'>3 


.31600 


.456 


.34876 


.489 


.38170 


.391 


.28457 


.424 


.31699 


.457 


.34975 


.49 


.38270 


.392 


.28554 


.425 


.31798 


.458 


.35075 


.491 


.38370 


.393 


.28652 


.426 


.31897 


.459 


.35175 


.492 


.38470 


.394 


.28750 


.427 


.31996 


.46 


.35274 


.493 


.38570 


.395 


.28848 


.428 


.32095 


.461 


.35374 


.494 


.38670 


.396 


.28945 


.429 


.32194 


.462 


.35474 


.495 


.38770 


.397 


.29043 


.43 


.32293 


.463 


.35573 


.496 


.38870 


.398 


.29141 


.431 


.32392 


.464 


.55673 


.497 


.38970 


.399 


.29'>39 


.432 


.32941 


.465 


.35773 


.498 


.39070 


.4 


.29337 


.433 


.32.590 


.466 


.35873 


.499 


.39170 


.401 


.29^35 


.484 


.32689 


.467 


.35972 


.5 


.39270 


.402 


.29533 


.435 


.32788 


.468 


.36072 






.403 


.29631 


.436 


.32887 


.469 


.36172 






.404 


.29729 


.437 


.32987 


.47 


.36272 







ber of diagonal crow foot braces that will be needed to sup- 
port the heads above the tubes, also the sectional area of 
each brace. The thickness of the head is % inch and 
the T.S. =55,000 pounds per square inch. 

Assume the head to be sufficiently strengthened by the 
flange for a distance of 2 inches from the shell, the diameter 
of the circle of which the segment above the tubes requires 
to be stayed is reduced by 2+2=4 inches and will there- 
fore be ^^ — 4=62 inches. The rise or height of the seg- 
ment above the tubes is 25 — 4=21 inches. Required, the 
area. 21-^62=. 338. Looking down the column headed 
^'Eatio'^ in Table 12, area opposite .338 is .23358. Area of 



Boiler Construction 115 

segment=.23358X62X62=897.88 square inches. The 
total pressure on this area will be 897.88X100=89,788 
pounds. 

Assume the braces to be made of 1% i^^ch round steel, 
having a T.S. of 50,000 pounds per square inch and to be 
designed in such a manner as to allow for loss of material 
in drilling the rivet holes in the crow feet. Each brace will 
have a sectional area of .994 square inches, and using 8 as 
a factor of safety, the strength or safe holding power of each 
stay may be found as follows: .994X50,000-^8=:6,212 
pounds, and the number of stays required= 89,788^ pounds 
(total pressure) divided by 6,212 pounds (strength of each 
stay) =14.5, or in round numbers 15. If the stays are 
made of flat bars of steel the sectional area should equal 
that of the round stays, and the dimensions of the crow feet 
of all stays should be such as to retain the full sectional 
area of the body after the rivet holes are drilled.. 

Each stay is connected to the plate by two %-inch rivets, 
having a T.S. of 55,000 pounds per square inch and a 
shearing strength of 45,000 pounds per square inch. These 
rivets are capable of resisting a direct pull of 10,818 pounds, 
using 5 as a factor of safety; ascertained as follows: 2A 
X45,000-^5=10,818=:strength of two rivets. They are 
also subjected to a crushing strain, and the resistance to 
this is DXC-^5, which expressed in figures is .875X90,000 
-^5=15,750 pounds. 

The proper spacing comes next, and is arrived at in the 
I following manner : 

Area to be stayed=897.88 square inches. 

Number of stays=15. 

Area supported by each stay=897.88-f-15=59.8 square 
inches. 



116 Steam Engineering 

The square root of 59.8=7.75 nearly, which is the dis- 
tance in inches each way that the stays should be spaced, 
center to center. 

If through stay rods are used in place of diagonal braces 
for staying the boiler under consideration, the number and 
diameter of the rods may be ascertained by the following 
method : 

Assuming the heads to be supported by channel bars, as 
previously described, and that the stays are pitched 14 
inches apart horizontally and 13 inches vertically, each stay 
would be required to support an area of 14X13=182 square 
inches, and the number of stays would be 897.88-^182= 
4.9, in round numbers 5. See Fig. 44. The pressure being 
100 pounds per square inch, the total stress on each stay= 
182X100=18,200 pounds. Assume the stay rods to be of 
soft steel having a T.S. of 50,000 pounds per square inch, 
and using a factor of safety of 8, the sectional area re- 
quired for each stay will be found as follows: 18,200X8^ 
50,000^:2.9 square inches, and the diameter will be found 
as follows: 2. 9-f-. 7854=3. 69, which is the square of the 
diameter, and the square root of 3.69=:1.9 inches, or prac- 
tically 2 inches. The same methods of calculation are ap- 
plicable to the staying of the heads below the tubes, also 
for stay bolts in fire box boilers. 

Strength of Unstayed Surfaces. A simple rule for find- 
ing the bursting pressure of unstayed fiat surfaces is that 
of Mr. Nichols, published in the "^^Locomotive,^^ February, 
1890, and quoted by Prof. Kent in his "Pocket-book.'' 
The rule is as follows: "Multiply the thickness of the 
plate in inches by ten times the tensile strength of the ma- 
terial used, and divide the product by the area of the head 
in square inches.'' Thus, 



Boiler Construction 117 

Diameter of head=66 inches. 
Thickness of head=% inch. 

Tensile strength= 55^000 pounds. 
Area of head= 3^421 square inches. 

■%X55,0O0Xl0-i-3,421=100, which is the number of 
pounds pressure per square inch under which the unstayed 
head would bulge. 

If we use a factor of safety of 8^ the safe working pres- 
sure would be 100^8=12.5 pounds per square inch, but 
as the strength of the unstayed head is at best an uncertain 
quantity it has not been considered in the foregoing calcu- 
lations for bracing, except as regards that portion of it that 
is strengthened by the flange. 

In all calculations for the strength of stayed surfaces, 
and especially where diagonal crow foot stays are used, the 
strength of the rivets connecting the stay to the flat plate 
must be carefully considered. A large factor of safety, 
never less than 8, should be used, and the cross section of 
that portion of the foot of the stay through which the rivet 
holes are drilled should be large enough, after deducting 
the diameter of the hole, to equal the sectional area of the 
body of the stay. 

Dished Heads, In boiler work where it is possible to 
use dished, or ^^bumped up'^ heads as they are sometimes 
called, this type of head is rapidly coming into use. Dished 
heads may be used in the construction of steam drums, also 
in many cases for dome-covers, thus obviating the necessity 
of bracing. The maximum depth of dish, as adopted by 
steel plate manufacturers April 4, 1901, is Vs ^^ ^^e diam- 
eter of the head when flanged, and if the tensile strength 
and quality of the plate from which the heads are made 
are the same as those of the shell plate, the dished head 



118 Steam Engineering 

becomes as strong as the shell, provided the head has the 
same thickness, or is slightly thicker than the shell plate. 

Welded Seams. A few boiler manufacturers have suc- 
ceeded in making welded seams, thus dispensing with the 
time-honored custom of riveting the plates together. A 
good welded joint approaches more nearly to the full 
strength of the material than can possibly be attained by 
rivets, no matter how correctly designed the riveted joint 
may be. The weld also dispenses with the necessity of 
caulking, and a boiler having a perfectly smooth surface 
inside, such as would be afforded by welded seams, would 
certainly be much less liable to collect scale and sediment 
than would one with riveted joints. But in order to make 
a success of welded seams the material used must be of the 
best possible quality, and great care and skill are required 
in the work. 

The Continental Iron Works of Brooklyn, New York^ 
exhibited at the St« Louis World^s Fair in 1904, a welded 
steel plate soda pulp digester without a single riveted joint. 
The dimensions of this vessel, which may be likened to a 
cylinder boiler without flues, were as follows: Thickness 
of plate, % inch; diameter, 9 feet; length, 43 feet. The 
heads were dished to the standard depth. The safe work- 
ing pressure was 125 pounds per square inch. It appears 
not only possible, but probable, that the process of welding 
boiler joints may in time supplant the older custom of 
riveting. 

QUESTIONS AND ANSWERS. 

79. What three principles should govern the design 
and construction of steam boilers ? 

Ans, First: They should be absolutely safe. Second: 



Boiler Construction 119 

They should be economical in the consumption of fuel. 
Third: They should be capable of furnishing dry steam. 

80. What is meant by the term tensile strength as ap- 
'plied to boiler material ? 

Ans. The number of pounds of pull that would be 
required to break a bar of the material in the direction of 
its length. 

81. What is liable to occur in case the tensile strength 
is too high ? 

Ans. Cracking of the sheets, also certain changes in the 
physical properties of the metal. 

82. Which are the stronger, punched or drilled plates? 
Ans, If the material is good soft steel, punched plates 

show a greater shearing resistance. 

83. What should be the tensile strength of rivet iron? 
Ans, About 60,000 pounds per square inch. 

84. What is a good test for a %-inch rivet? 

Ans, It should stand being doubled up and hammered 
together cold without being fractured. 

85. What is the shearing resistance of iron rivets ? 
Ans, About 85 per cent of the original bar. 

86. What is the shearing resistance of steel rivets ? 
Ans, 77 per cent of the original bar. 

87. What is meant by efficiency of the joint? 

Ans. The percentage of strength of the solid plate, that 
is retained in the joint. 

88. What should be the style of joint with sheets thicker 
than % inch? 

Ans, It should be a double butt joint. 

89. What should be the ratio of diameter of rivet to 
thickness of plate for double butt joints? 



120 Steam Engineering 

Ans, The diameter of the rivet should be about 1.8 
times the thickness of sheet. 

90. What should be the pitch of rivets? 
Ans. Three and one-half to four times the diameter of 

the hole. 

91. Describe the triple riveted butt joint. 
Ans. It has two welts or straps^ one inside^ and one 

outside. 

92. Is this a good form of joint? 
Ans. It IS. 

93. What type of joint gives the highest efficiency? 
Ans. A joint in which the tensile strength of the rods 

from which the rivets are cut approaches that of the plates^ 
and when the proportions of the joint are such^ that the ' 
tensile strength of the rivets, and the crushing resistance 
of the rivets and plate, for a given, or unit strip, are as 
nearly equal as it is possible to make them. 

94. In how many ways may failure occur in a double 
riveted butt joint? 

Ans. In five distinct ways. 

95. Name the first manner of failure. 
Ans. Tearing of the plate at outer row of rivets. 

96. What is the second? 
Ans. Shearing two rivets in double shear, and one in 

single shear. 

97. What is the third manner of failure? 
Ans. Tearing of the plate at inner row of rivets, and 

shearing one rivet in the outer row. 

98. Describe the fourth method of failure. 
Ans. Crushing in front of three rivets. 

99. What is the fifth manner of failure? 
Ans. Crushing in front of two rivets, and shearing one. 



Questions and Answers 121 

100. How may a triple riveted butt joint fail? 

Ans. First : By tearing the plate at the outer row of 
rivets. Second: By shearing four rivets in double shear, 
and one in single shear. Third: Eupture of the plate at 
the middle row of rivets, and shearing one rivet. Fourth : 
Crushing in front of four rivets, and shearing one rivet. 

101. What is the efficiency of- the quadruple riveted 
butt joint? 

Ans, In some cases as high as 94 per cent. 

102. In what four ways may failure occur in this type 
of joint? 

Ans. First: By tearing the plate at the outer row of 
rivets. Second : By shearing eight rivets in double shear, 
and three in single shear. Third : By tearing at inner row 
of rivets, and shearing three rivets. Fourth : By tearing at 
first outer row of rivets where the pitch is 7I/2 inches. 

103. What is implied in the staying of a flat surface? 
Ans. Holding it against pressure at a series of isolated 

points, which are arranged in symmetrical order. 

104. Does the cylindrical shell of a boiler need bracing? 
Ans. No. 

105. Why is this? 

Ans. Because the internal pressure tends to keep it 
cylindrical. 

106. How are the heads sometimes stayed? 

Ans. By through stay rods of soft steel, or iron 114 or 
,2 inches in diameter extending through from head to head. 

1107. What advantage has this form of stays? 
Ans. The pull is at right angles to the plate. 
• 108. What other methods of bracing the heads of high 
(pressure boilers are used? 

Ans. Gusset stays, and dished heads. 



122 Steam Engineering 

109. What is the minimum factor of safety for stays, 
and braces? 

Ans. Eight. 

110. Give a simple rule for finding the bursting pres- 
sure of unstayed flat surfaces. 

Ans. Multiply the thickness of the plate in inches by 
ten times the tensile strength and divide the product by 
the area of the surface in square inches. 



aiif 
fltfc 

500 
liiii' 
iiini 
Hi 



Boiler Setting and Equipment 

Setting. In the following remarks concerning boiler 
settings reference is had chiefly to the horizontal tabular 
boiler. Owing to the many and varied styles of water-tube 
boilers no prescribed set of rules is applicable, each builder 
of this type of boiler having a set plan of his own for the 
brick work, and these plans have already been illustrated 
and described in the section on water-tube boilers. In the 
case of internally fired boilers the matter of setting re- 
solves itself into the simple point of securing a sufficiently 
solid foundation, either of stone or brick laid in cement, 
for the boiler to rest upon. 

In the case of the horizontal tubular boiler, there are 
two methods of support, one by suspension from I-beams 
and girders, which has already been fully described; the 
other by supporting the boiler upon brackets riveted to the 
side sheets, and resting upon the side walls, and in such 
settings particular attention should be paid to securing a 
good foundation for the walls and great care exercised in 
building them in such manner that the expansion of the 
inner wall or lining will not seriously affect the outer walls. 
This can be done by leaving an air space of two inches in 
the rear and side walls, beginning at or near the level of 
the grate bars and extending as high as the fire line, or 
about the center line of the boiler. Above this height the 
wall should be solid. Fig. 48 shows a plan and an end ele- 
vation illustrating this idea. The ends of some of the 
oricks should be allowed to project at intervals from th^ 

123 



124 



Steam Engineering 



outer walls across the air space^ so as to come in touch with 
the inner walls. 

Where boilers are set in batteries of two or moi e, the 
middle or party walls should be built up solid from the 
foundation. All parts of the walls with which the fire 
comes in contact should be lined with fire brick, every 
fifth course being a header to tie the lining to the main 
wall. 





Fig. 48 



Bridge walls should be built straight across from wall 
to wall of the setting, and should not be curved to conform . 
to the circle of the boiler shell. The proper distance from 
the top of the bridge wall to the bottom of the boiler varies 
from eight to ten inches, depending upon the size of the 
boiler. The space back of the bridge wall, called the com- 
bustion chamber, can be filled in with earth or sand, and 
should slope gradually downward from the back of the 
bridge wall to the floor level at the rear wall, and should 
be paved with hard burned brick. The ashes and soot can 
then be easily cleaned out by means of a long-handled hoe 
or scraper inserted through tbe cleaning out door, which 
should always be placed in the back wall of every boiler set- 
ting. 

Back Arches, A good and durable arch can be made 
for the back connection, extending from the back wall to 



Boiler Setting and Equipment 



125 



the boiler head, by taking flat bars of iron % x 4 inches, 
cutting them to the proper length and bending them in 
the shape of an arch, turning 4 inches of each end back 




Fig. 49 







Fig. 50 



at right angles, as shown in Fig. 49. The distance 0-B 

Should equal that from the rear wall to the boiler head, 

and the height, 0-A, should be about equal to 0-B, and 

J should bring the point A about two inches above the top 



126 



Steam Engineering 



TOW of tubes. The clamp thus formed is filled with a 
course of side arch fire brick. Fig. 50, and will form a 
complete and self-sustaining arch, the bottom, B, resting 
on the back wall, and the top. A, supported by an angle 
iron riveted across the boiler head about three inches above 
the top row of tubes. See Figs. 51 and 52. 

Enough of these arches should be made so that when 
laid side by side they will cover the distance from one side 




Fig. 51 

wall to the other across the rear end of the boiler. A fifty- 
four-inch boiler would thus require six clamps, a sixty- 
inch boiler seven clamps, and a seventy-two-inch boiler 
w^ould require eight clamps ; the length of a fire brick being 
about nine inches. In case of needed repairs to the back' 
end of the boiler the sections can be lifted off, thus giving 
free access to all parts, and when the repairs are completed 
the arches can be reset with very little trouble and much 
less expense than the building of a solid arch would neces- 



Boiler Setting and Equipment 127 

sitate. This form of segmental arch allows ample freedom 
for expansion of the boiler, in the direction of its length, 
without leaving an opening when the boiler contracts. 

The crosswise construction of arch bars, while affording 
equal facility in repair work, is necessarily more expensive 
than the form here described, and is also open to the objec- 
tion that it cannot follow the contracting boiler and main- 
tain a tight joint or connection between the back arch and 
the rear head above the tubes. 

Boiler walls should always be well secured in both direc- 
tions by tie rods extending throughout the entire length 

, and breadth of the setting, whether there be one boiler or a 
battery of several. The bottom rods should be laid in place 

f at the floor level when starting the brick work, and the top 
rods extending transversely across the boilers can be laid 
on top of the boilers. The top rods extending from front 

t to back can be laid in the side walls, or rest on top of them. 
All tie rods should be at least one inch in diameter, and 
for batteries of several boilers they should be larger. The 

irods should extend three or four inches beyond the brick 
work, with good threads and nuts on each end to receive 
the buck stays. In laying down the transverse tie rods 

i they should be located so as to allow the buck stays to bind 
the brick work where the greatest concentration of heat 
occurs. 

Horizontal boilers should always be set at least one inch 
i lower at the back end than at the front, to make sure that 
i the rear ends of the tubes will be covered with water so long 
I as any appears in the gauge glass, provided of course that 
tthe lower end of the glass is properly located with reference 
ito the top row of tubes, which will be discussed later on. 
Upon the brick work and immediately under each lug of 



128 Steam Engineering 

the boiler there should be laid in mortar a wrought or cast 
iron plate several inches larger in dimension than the bear- 
ing surface of the lug and not less than one inch in thick- 
ness. Upon each of these plates there should be placed 
two rollers made of round iron 1 or 1% in. in diameter, 
and as long as the width of the lug. These rollers should 
be placed at right angles to the length of the boiler, in 
such a position that the lug will bear equally upon them. 
The object of the rollers is to prevent disturbance of the 
brick work by the endwise expansion and contraction of 
the boiler. 

It will bo found very convenient when making tests to 
have an opening into the combustion chamber back of the 
bridge-wall, also in the back wall opposite the tubes, to in- 
sert a pyrometer, or to connect a draft gage or gas sampler. 
This can be accomplished by inserting a li/4-inch pipe in 
the wall flush with each side, and screwing a cap on the 
outside. The inner end can be packed with asbestos fiber. 
A %-inch hole drilled in the delivery pipe between the 
valve and the nozzle will save drilling one by hand when 
it is desired to insert a calorimeter. 

Grate Surface. The number of square feet of grate sur- 
face required depends upon the size of the boiler. A good 
rule and one easy to remember is to make the length of the 
grates equal to the diameter of the boiler. The width, of 
course, will depend upon the construction of the furnace. 
If the fire brick lining is built perpendicular, the width of 
grate will be about equal to the diameter of the boiler. 
On the other hand, if the lining is given a batter of three 
inches, starting at the level of the grate, then the width 
will be reduced six inches. It is customary to allow one 
square foot of grate surface to every 36 sq. ft. of heating^ 



Boiler Setting and Equipment 129 

surface. The distance of the grate-bars from the shell of 
the boiler varies from 24 to 28 in., according to the dimen- 
sions of the boiler. 

Insulation All boilers should be well protected from 
the cooling influence of outside air, if economy of fuel is 
any object. The tops of horizontal boilers should be 
covered with some kind of heat insulating material, or 
arched over with common brick, leaving a space of two 
inches, starting at the level of the grate, then the width 
saving in fuel will far more than compensate for the extra 
expense in a very short time. All cracks in the side and 
rear walls should be carefully pointed up with mortar or 
fire clay. One source of heat loss in return flue boilers is 
short circuiting from the furnace to the breeching, caused 
by the arches over the fire doors becoming loose and shaky, 
and allowing* considerable of the heat to escape directly to 
the stack instead of passing under the boiler and through 
the tubes. Another bad air leak often occurs at the back 
connection when the arch rests wholly upon iron bars im- 
bedded in the side walls. This leak, as has already been 
noted, is caused by the expansion of the boiler, which 
gradually pushes the arch away from the back head until, 
in the course of time, there will be a space of % inch and 
sometimes % inch between the head and the arch. The 
obvious remedy for this is an arch that will go, and come 
with the movement of the boiler, and such an arch can be 
secured by building it in sections, as illustrated by Fig. 52, 
and then riveting a piece of angle iron to the boiler head, 
above the top row of tubes for the upper ends of the sec- 
tions to rest upon, as already described. It- will be seen 
that within all possible range of boiler movement in either 
direction the arch will, with this construction, always re- 
main close to the head. 



130 



Steam Engineering 



Water Columns. Water columns should be so located 
as to bring the lower end of the gauge glass exactly on a 
level with the top of the upper row of tubes, thus always 
affording a perfect guide as to the depth of water over the 
tubes. Many gauge glasses are placed too low, and water 
tenders and firemen are often deceived by them, unless their 
positions with relation to the tubes are carefully noted. 




Fig. 52 



The only safe plan for an engineer to pursue in taking 
charge of a steam plant is to seize the first opportunity for 
noting this relation. When he has washed out his boilers 
he may leave the top man-hole plates out while refilling 
them, and when the water stands at about four inches over 
the top row of tubes, the depth of water in the glass should 
be measured. He should do this with every boiler in the 
plant, and make a memorandum for each boiler. He will 



Boiler Setting and Equipment 131 

then know his bearings with regard to the safe height of 
water to be carried in the several gauge glasses. If he finds 
any of them are too low, he should lose no time in having 
them altered to conform to the requirements of safety. 
The' position of the lower gauge cock should be three 
inches above the top row of tubes. 

In making connections for the water column plugged 
crosses should always be used in place of ells. Brass plugs 
are to be preferred if they can be obtained ; but whether of 
brass or iron, they should always be well coated with a paste 
made of graphite and cylinder oil before they are screwed 
in. They can then be easily removed when washing out the 
boiler, so as to allow the scale, which is sure to form in the 
lower connection, to be cleaned out. The best point at 
which to connect the lower pipe with the boiler is in the 
lower part of the head just below the bottom row of tubes, 
and near the side of the boiler on which the water column 
is to stand; 1^/4 or 11/2 in. pipe should be used in all cases. 
The top connection can be made either in the head near 
the top, or in the shell. A % or 1 in. drain pipe should be 
led into the ash pit, fitted with a good reliable valve which 
should be opened at frequent intervals to allow the mud 
and dirt to blow out of the water column and its connec- 
tions. This is a very important point, and great care should 
be taken to keep the water column and all its connections 
thoroughly clean at all times. 

One of the best indications that some portion of the 
connections between the water glass and the boiler is choked 
or plugged with scale, is when there is no perceptible move- 
ment of the water in the glass. When the connections are 
free and the boiler is being fired, there is always a slight 
movement of the water up and down in the glass, and when 



132 Steam Engineering 

there is no perceptible movement it is time to look for the 
cause at once. Many instances of burned tubes have oc- 
curred, and even explosions caused by low water in boilers 
while the gauge glass showed the water to be at a safe 
height. But owing to the connections having become 
plugged with scale^ the water in the glass had no connec- 
tion whatever with that in the boiler, and the water column 
was therefore worse than useless. 

The above remarks apply particularly to horizontal re- 
turn tubular boilers. In the case of water tube boilers the 
location of the gauge glass as regards height is governed 
by the desired level of the water in steam drum, or dnims^ 

Steam Gauges, As water columns are made at present 
th^ steam gauge is usually connected at the top of the col- 
umn. This makes a handsome and convenient connectioUj 
although theoretically the proper method would be to con- 
nect the steam gauge directly with the dome, or the steam 
space of the shell. There should always be a trap or siphon 
in the gauge pipe in order to retain the water of condensa- 
tion, so as to prevent the hot steam from coming in con- 
tact with the spring. 

If at any time the water is drained from the siphon, care 
should be exercised in turning on the steam again by al- 
lowing it to flow in very slowly at first until the siphon is 
again filled with water. 

There are different types of steam gauges in use, but the 
one most commonly used, and which no doubt is the most 
reliable, is known as the Bourdon spring gauge (see Pig- 
53). This gauge consists of a thin, curved, flattened metal- 
lic tube, closed at both ends and connected to the steam 
space of the boiler by a small pipe, bent at some portion of 
its length into a curve or circle that becomes fllled with 



Boiler Setting and Equipment 



133 



water of condensation^ and thus prevents the hot live steam 
from coming directly in contact with the springy while at 
the time the full pressure of steam in the boiler acts upon 




Fig. 53 

AUXILIARY SPRING PRESSURE GAUGE, SECTIONAL VIEW 

!the springs tending to straighten it. The end or ends of 
Ithe spring being free to move, and connected by suitable 
geared rack and pinion with the pointer of the irauL'^e. tliis 



134 



Steam Engineering 



hand or pointer is cansed to move across the dial^ thns indi- 
cating the pressure of steam per square inch in the boiler. 
When there is no pressure in the boiler the hand should 
point to 0. 




Fig. 54 

AUXILIARY SPRING PRESSURE GAUGE 

Steam gauges should be tested frequently by comparing 
them with a test gauge that has been tested against a col- 
umn of mercury. 

The steam gauge and the safety valve should be com- 
pared frequently by raising the steam pressure high enough 
to cause the valve to open at the point for which it is set 
to blow. 



I 



Boiler Setting and Equipment 



135 



Safety Valves, The modern pop valve is generally re- 
liable, but, like everything else, if it is allowed to stand 
idle too long it is likely to become rusty and 'stick. There- 
fore it should be allowed to blow off at. least once or twice 
a week in order to keep it in good condition. 

Most pop valves for stationary boilers are provided with 
a short lever, and if at any time the valve does not pop 
when the steam gauge shows the pressure to be high 
enough, it can generally be started by a light blow on the 
lever with a hammer. 




-- -d 

Fig. 55 



The ratio of safety valve area to that of grate surface is, 
for the old style lever and weight valve, 1 sq. in. of valve 
area for each 2 sq. ft. of grate surface, and for pop valves 
1 sq. in. of valve area for each 3 sq. ft. of grate surface. 

Each boiler in a battery should have its own safety valve, 
and, in fact, be entirely independent of its mates as regards 
safety appliances. 

One example of safety valve computation will be given. 
Suppose the grate surface of a boiler is 5X^=30 sq. ft.. 



136 Steam Engineering 

what should be the diameter of the lever safety valve? 
The required area of the valve is 30-f-2=15 sq. in. Then 
15-:-. 7854= 19, which is the square of the diameter of the 
valve. Extracting the square root of 19 gives 4.35 in. 
diameter of valve. In actual practice one 5 in. or two 3 in. 
lever safety valves would be required. If a pop valve is 
to be used the required area is 30-^3=10 sq. in. Then 
10-^. 7854=12. 73=square of diameter of valve. Extract 
the square root of 12.73 and the result is 3.6 in.:=diameter 
of valve. In practice a 4-in. valve would be required. 

Eegarding the pressure at which a spring-loaded, or pop 
safety valve will blow off, it is first necessary to ascertain 
by experiment the force required to compress the spring. 
The pressure at which a spring will yield depends not only 
upon the shape and size of the material of which it is made, 
the diameter, number and pitch of the coils, all of which 
are measurable and determinable, but upon the nature and 
condition of the material itself. 

For instance, a spring of brass will compress with less 
pressure than one of steel, similar in every other respect, 
and there is such a wide difference in steels that there will 
be a great deal of difference in the action of steel springs 
according to the kind of metal, degree of temper, etc. 

The following rule may be used in calculations of this 
character : 

RULE. 

Multiply the compression in inches hy the fourth power 
of the thickness of the steel in sixteenths of an inch, and 
by 22 for round or 30 for square steel. Product I, 

Multiply the cube of the diameter of the spring, meas- 
ured from center to center of the coil (as on the line d, in 
Fig. 55) in. inches, hy the number of free coils in th^ 



Boiler Setting and Equipment 137 

spring, and iy the area of the valve in square inches. 
Product II. 

Divide Product I by Product II and the quotient will be 
the pressure per square inch at which the valve will blow 
off. 

With a dead weight or a lever-loaded valve the force re- 
quired to lift it remains the same^ no matter how high the 
valve lifts. The weights weigh no more if they are raised 
an inch or two, and the leverage does not change, but with 
the spring-loaded valve, the more the valve lifts the more 
the spring is compressed, and the more force is required 
to com,press or hold it. It follows then that if an ordinary 
valve were loaded with a spring it would simply crack open 
and commence to sizzle when the pressure equaled the 
force at which the spring was set, and that if this were 
not enough to relieve the boiler the pressure would have 
to increase, opening the valve more and more until the 
steam blew off as fast as it was made. 

But the ideal valve should stay on its seat until the 
pressure reaches the desired limit, then open wide and dis- 
charge the excess. This result is accomplished by the con- 
struction shown in Fig. 56. With the first opening of the 
valve the steam passes into the little "huddling chamber^' 
made by the cavity near the overhanging edge of the valve, 
and a similar cavity surrounding the seat. The pressure 
which accumulates here, acting on the additional area of 
the valve, raises it sharply with the "pop^^ which gives the 
valve its name, and it is sustained by the impact and re- 
action of the issuing steam, until the pressure has subsided 
sufficiently to allow the spring to overcome these actions. 

A short space will be devoted to the consideration of the 
lover safety valve also, as it may be of interest to some 
student?. 



138 



Steam Engineering 



The U. S. marine rule for lever valves is here repeated: 
^^Lever safety valves to be attached to marine boilers shall 
have an area of not less than one square inch to every two 




Fig. 56 
square feet of grate surface in the boiler^ and the seats of 
all such safety valves shall have an angle of inclination of 
45^ to the center line of their axis/^ 



Boiler Setting and Equipment 



139 




Fig. 57 
» inside view of a pop safety valve 

In order to arrive at accurate results in lever safety 

' valve calculations it is necessary to know first the number 

of pounds pressure exerted upon the stem of the valve by 



140 Steam Engineering 

the lever itself, irrespective of the weight, also the weight 
of the valve and stem, as all these weights, together with the 
weight of the ball suspended upon the lever tend to hold 
the valve down against the pressure of the steam. The 
effective weight of the lever can be ascertained by leaving it 
in its position attached to the fulcrum, and connecting a 
spring balance scale to it at a point where it rests on the 
valve stem. The weight of the valve and stem can also be 
found by means of the scale. When the above weights are 
known, together with the weight at the end of the lever and 
its distance from the fulcrum, also the area of the valve and 
its distance from the fulcrum, the pressure at which the 
valve will blow can be found by the following rules : 

Rule 1, Multiply the weight by its distance from the 
fulcrum. Multiply the weight of the valve and lever by 
the distance of the stem from the fulcrum and add this to 
the former product. Divide the sum of the two products 
by the product of the area of the valve multiplied by the 
distance of its stem from the fulcrum. The result will 
be pressure in pounds per square inch required to lift 
the valve. 

Example. Diameter of valve, 3 in. 

Distance of stem from fulcrum, 3 in. 

Effective weight of- lever, valve and stem, 20 lbs. 

Weight of ball, .50 lbs. 

Distance of ball from fulcrum, 30 in. 

Eequired pressure at" which the valve will blow off, 50X 
30+20X3=1560. 

Area of valve, 7.0686X3=21.2058. 

1560—21.2058=73.57 pounds pressiire. 

When the pressure at which it is desired the valve should 
blow off is known, together with the weights of all the 



Boiler Setting and Equipment 141 

parts^ the proper distance from the fulcrum at which to 
place the weight is ascertained by Eule 2. 

Rule 2. Multiply the area of the valve by the pressure^ 
and from the product subtract the effective weight of the 
valve and lever. Multiply the remainder by the distance 
of the stem from the fulcrum^ and divide by the weight 
of the ball. The quotient will be the required distance. 

Example, Area of valve^ 7.07 square inches. 
To blow off at 75 pounds. 

Effective weight of lever and valve/ 20 pounds. 
Weight of ball, 50 pounds. 
Distance of valve stem from fulcrum, 3 inches. 
7.07X75—20=510.25. 

510.25 X3-i-50=:30. 6 inches, distance from fulcrum at 
which to place the ball. 

When the pressure is known, together with the distance 
of the weight from the fulcrum, the weight of the ball is 
obtained by Eule 3. 

Rule S. Multiply the area of the valve by the pressure, 
and from the product subtract the effective weight of the 
lever and valve. Multiply the remainder by the distance 
of the stem from the fulcrum, and divide by the distance 
of the ball from the fulcrum. The quotient will be the 
required weight. 

Example, Area of valve, 7.07 square inches. 

Pressure in pounds per square inch, 80 pounds. 

Effective weight of lever and valve, 20 pounds. 

Distance of stem from fulcrum, 3 inches. 

Distance of weight from fulcrum, 30 inches. 

7.07X80—20=545.6. 

545.6X3-^30=54.56 pounds, weight of ball. 



142 Steam Engineering 

Safety valves^ especially those of the lever type^ are 
liable to become corroded and stick to their seats if allowed 
to go any great length of time without blowing. There- 
fore it is good practice to raise the steam pressure to the 
blowing off point at least two or three times a week, or 
oftener^, for the purpose of testing the valve. If it opens 
and releases the steam at the proper point all is well, but 
if it does not, it should be looked after forthwith. Gener- 
ally the mere raising of the lever by hand, or a few taps 
with a hammer if it be a pop valve, will free it and cause 
it to work all right again; but if this treatment has to be 
resorted to very often the valve should be taken down and 
overhauled. In too many steam plants not enough im- 
portance is attached to the safety valve. The fact is, it is 
one of the. most useful and important adjuncts of a boiler, 
and if neglected serious results are sure to follow. 

Fusille Plugs. A fusible plug should be inserted in 
that part of the heating surface of a boiler which is first 
liable to be overheated from lack of water. 

In a horizontal tubular, or return flue boiler the proper 
location for the fusible plug is in the back head about 
1% or 2 inches above the top row of tubes. In fire-box 
boilers the plug can be put into the crown sheet directly 
over the fire. These plugs should be made of brass with i 
hexagon heads and standard pipe threads, in sizes ^/4, %, 
1 inch, or even larger if desired. A hole drilled axially 
through the center, and countersunk in the end that enters 
the boiler is filled with an alloy of such composition that 
it will melt and run out at the temperature of the dry 
steam at the pressure carried in the boiler. Thus, if the 
water should get below the plug the dry steam, coming in 
contact with the fusible alloy, melts it and, escaping 



Boiler Setting and Equipment 143 

through the hole in the plug^ gives the alarm^ and in case 
of fire-box or internally fired boilers the steam will gener- 
ally extinguish the fire also. The hole is countersunk on 
the inner end of the plug so as to retain the fusible metal 
against the boiler pressure. These plugs should be looked 
after each time the boilers are washed out^ and all dirt 
and scale should be cleaned off in order that the fusible 
metal may be exposed to the heat. 

Another type of fusible plug consists of a small brass 
cylinder into one end of which is screwed a plug filled with 
a metal which will fuse at the temperature of dry steam 
at the pressure which is to be carried in the boiler. The 
other end of the cylinder is reduced and fitted with a small 
stop valve and threaded to screw into a brass bushing in- 
serted into the top of the boiler shell. This bushing also 
receives at its lower end a piece of % or %-inch pipe which 
extends downwards to within 2 inches of the top row of 
tubes^ or the crown shee't^ if the boiler is internally fired. 
The principle of the device is that in case the water falls 
below the lower end of the pipe^ steam will enter^ fuse the 
metal in the plug^, and be free to blow and give warning of 
danger. Som,e of these appliances are fitted with whistles 
which are sounded in case the steam gets access to them. 
But even with such devices, no engineer can afford to relax 
his own vigilance and depend entirely upon the safety ap- 
pliances to prevent accidents from low water. 

Domes and Mud Drums, As a general proposition^ both 
mud drums and domes are useless appendages to steam 
boilers. There are, no doubt, instances where they may 
serve a purpose, but as a rule their use is of no advantage 
ito a boiler. Neither are the so-called circulating systems, 
sometimes attached to return tubular boilers, of any real 



144 Steam Engineering 

value. These consist of one or more 4 to 6-inch pipes 
extending under the boiler from front to back through the 
furnace^ and the combustion chamber and connected to each 
end of the boiler. 

Blow Off Pipes, Blow off pipes should always be con- 
nected with the lowest part of the water space of a boiler. 
If there is a mud drum^ then of course the blow off should 
be connected with it; but if there is no mud drum^ the 
blow off should connect with the bottom of the shelly near 
the back head^ extend downwards to the floor of the com- 
bustion chamber^ and thence horizontally out through the 
back wall^ where the blow off cock can be located. 

The best blow off cocks are the asbestos packed^ iron-body 
plug cocks^ which are durable and safe. A globe valve 
should never be used in a blow off pipe^ because the scale 
and dirt will lodge in it and prevent its being closed tight- 
ly. A straight way, or gate valve is not so bad^ but an 
asbestos packed plug cock is undoubtedly the best and safest. 

In order to protect the blow off pipe from the intense 
heat^ a shield consisting of a piece of larger pipe can be 
slipped over the vertical part before it is connected. 

Blow off cocks should be opened for a few seconds once 
or twice a day, to allow the scale and mud to be blown out. 
If neglected too long they are liable to become filled with 
scale and burn out. A plan which is said to give good re- 
sults is to connect a tee in the horizontal part of the pipe, 
and from this tee run a 1 inch pipe to a point in the back 
head at the water level. It is claimed that this will cause 
a circulation of water in the pipe, and prevent the forma- 
tion of scale. 

A surface blow off* is a great advantage, especially if the 
water is muddy or liable to foam. By having the surface 



Boiler Setting and Equipment 145 

blow off connected on a level with the water line a large 
amount of mud, and other matter which is kept on the 
surface by the constant ebullition can be blown out. 

A combination surface blow off, bottom blow off^ and cir- 
culating system can be arranged by a connection such as 
illustrated in Fig. 58. By closing cock A and opening 
cocks B and C the bottom blow off is put in operation; by 
closing B and opening A and C the surface blow off is 
started, an-d by closing C and leaving A and B open the 
device will act as a circulating system. The pipe should 
be of the same size throughout. Blow off pipes should be 
of ample size, never less than 11/4 inch, and from that to 
2% inch, depending upon the size of the boiler. 

Feed Pipes. Authorities differ in regard to the proper 
location of the inlet for the feed pipe, but upon one point 
all are agreed, namely, that the feed water, which is al- 
ways at a lower temperature than the water in the boiler, 
should not be allowed to come directly in contact with the 
hot boiler sheets until its temperature has been raised to 
within a few degrees of the temperature of the water in 
the boiler. Certainly one of the most fruitful sources of 
leaks in the seams, and around the rivets, is the practice of 
introducing the feed water into the bottom either at the 
back or front ends of boilers, as is too often the case. The 
cool water coming directly in contact with the hot sheets 
causes alternate contraction and expansion, and 'results in 
leaks, and very often in small cracks in the sheet, the cracks 
extending radially from the rivet holes. It would appear 
ithat the proper method is to connect the feed pipe either 
into the front head just above the tubes, or into the top 
tof the shell. The nipple entering the boiler should have 
a» long thread cut on the end which screws into the sheet. 



146 



Steam Engineering 



and to this end, inside the boiler there should be connected 
another pipe which shall extend horizontally at least two- 
thirds of the length of the boiler, resting on top of the tubes, 
and then discharge. Or, what is till better, allow the in- 
ternal pipe to extend from the entering nipple at the front 




Fig. 58 

end to within a few inches of the back head, then at right 
angles across the top of the tubes to the other side, and from 
there discharge downward. By this method the feed water 
is heated to nearly, if not quite, the temperature of the 
water in the boiler before it is discharged. One of the 
objections to this system is the liability of the pipe inside 



Boiler Setting and Equipment 147 

the boiler to become filled with scale and finally plugged 
entirely. In such cases the only remedy is to replace it 
with new pipe. But the great advantage of having the water 
thoroughly heated before being discharged into the boiler 
will much more than compensate for the extra expense of 
piping, and the general idea of introducing the feed water 
at the top, instead of at the bottom of the boiler is there- 
fore recommended as being the best. 

The diameters of feed pipes range from 1 inch for small 
sized boilers, up to l^/o and 2 inches for boilers of 54 to 72 
inches in diameter. It is not good policy to have the feed 
pipe larger than necessary for the capacity of the boiler; 
because it then acts as a sort of cooling reservoir for the 
feed water, and may cause considerable loss of heat. 

For batteries of two or more boilers it is necessary to 
run a main feed header, with branch pipes leading to each 
boiler. The header should be large enough to supply all 
: the boilers at the same time, should it ever become necessary 
to do so. The header can be run along the front of the 
boilers just above the fire doors, with the branch pipes 
running up on either side, clear of the flue doors and enter- 
ing the front connection, or smoke arch, and the boiler head 
at a point two inches above the tubes. There should always 
be a valve in each branch pipe, between the check valve and 
;the header for the purpose of regulating the supply of 
?water to each boiler, and also for shutting off the pump 
pressure in case of needed repairs to the check valve. An- 
other valve should be placed between the check valve and 
the boiler. By this arrangement it is always possible to get 
'at the check valve when it is out of order. 



148 Steam Engineering 

FEED PUMPS. 

Feed Pumps and Injectors. The belt driven power pump 
is the most economical boiler feeder^ but is not the most 
convenient nor the safest. When the engine stops, the pump 
stops also, and sometimes it happens that the belt gives 
vray, and the pump stops at just the time when the boiler 
is being worked the hardest. 

The modern double acting steam pump, of which there 
are many different makes to choose from, is without doubt 
the most reliable boiler feeding appliance and the one best 
adapted to all circumstances and conditions, although it is 
not economical in the use of steam, since the principle of 
expansion cannot be carried out with the pump as with the 
engine. 

In selecting a feed pump care should be exercised to see 
that it is of the proper size and capacity to supply the 
maximum quantity of water that the boiler can evaporate. 
This may be ascertained by taking into consideration the 
amount of heating surface and the required consumption 
of coal per square foot of grate surface per hour. First, 
take the coal consumption. Assume the boiler to have 30 
square feet of grate surface, and that it is desired to burn 
15 pounds of coal per square foot of grate per hour, which 
is a good average with the ordinary hand fired furnace 
using bituminous coal. Suppose the boiler is capable of 
evaporating 8 pounds of water per pound of coal consumed. 
Then 80X15X8=3,600 pounds of water evaporated per 
hour. Dividing 3,600 by 62.4 (the weight of a cubic foot 
of water in pounds) gives 57.6 cubic feet per hour, which, 
divided by 60, gives 0.96 cubic feet per minute. This multi- 
plied by 1,728 (number of cubic inches in a cubic foot) 
gi^^es 1,659 cubic inches per minute which the pump is 



fe 
k 
of 

811 



Boiler Setting and Equipment 149 

required to supply. Suppose the pump is to make forty 
strokes per minute^ and the length of stroke is five inches. 
Then 1^659-^40=41.47 cubic inches per stroke^, which, 
divided by 5 (length of stroke in inches) gives 8.294 square 
inches as the required area of water piston. 8. 294-:-. 7854=: 
10.56, which is the square of the corresponding diameter, 
and the square root of 10.56=3.25. So, theoretically, the 
size of the water end of the pump would be 3^/4 inches in 
diameter by 5 inches stroke; but as it is always safer to 
have a reserve of pumping capacity, the proper size of the 
pump would be 3^/2 inches in diameter, by 5 inches stroke, 
with a steam cylinder of 6 or 7 inches in diameter. 

There is another rule for ascertaining the size of the 
feed pump, viz., by taking the number of square feet of 
heating surface in the boiler and allow a pump capacity 
of 1 cubic foot per hour for each 15 square feet of heating 
surface. Thus, let the total heating surface of the boiler 
be 786 square feet. Dividing this by 15 gives 52.4 as the 
number of cubic feet of water required per hour, from which 
the pump dimensions may be found in the same way as in 
the preceding case. 

! In figuring on the capacity of a feed pump for a bat- 
itery of two or more boilers, the total quantity* of water 
* required by all the boilers must be taken into consideration. 
'All boiler-rooms should be supplied with at least two feed 
pumps, so that if one breaks down there may always be 
another one available. 
^' Hard rubber valves are, all things considered, the best 
for a boiler feed pump, as they are not affected by hot 
"water and do not hammer the seats like metallic composi- 
tion valves do. Every boiler feed pump should be fitted 
'with a good sight-feed lubricator for cylinder oil. The 



.150 Steam Engineering 

steam valve mechanism of a steam pump is very sensitive 
and delicate^ and requires good lubrication in order to do 
good work. In too many cases feed pumps are fitted with 
an old style cylinder oil cup and there is generally more oil 
on the outside of the valve chest than there is inside, while 
the valve is bulldozed into working by frequent blows- from 
a convenient club. 

The steam valves of all steam pumps are adjusted before 
they are sent out from the factory, and most of them are 
arranged so that the stroke may be shortened or lengthened 
as the engineer desires. It is best, as a rule, to allow a 
pump to make as long a stroke as it will without striking 
the heads, because then the parts are worn evenly. 

Sometimes an engineer is called upon to set the valves of 
a duplex pump which have become disarranged. In such a 
case he should proceed as follows: Place both pistons ex- 
actly at mid-stroke. This may be done in two ways. First, 
by dropping a plummet line alongside the levers connecting 
the rock shafts with the spools on the piston rods. Then 
bring the rods to the position where the centers of the 
spools will be in a vertical line with the centers of the 
rock shafts. 

The se'cond method is to move the piston to the ex- 
treme end of the stroke until it comes in contact with the 
cylinder head. Then mark the rod at the face of the stuffing 
box gland. Next move the piston to the other end of the 
stroke and mark the rod at the opposite gland. Now make 
a mark on the rod exactly half way between the two out- 
side marks and move the piston back until the middle mark 
is at the face of the gland and the piston will be at mid- 
stroke. Having placed both pistons at mid-stroke, remove 
the valve chest covers, and adjust the valves in their central 



Boiler Setting and Equipment 



151 



position^ viz.^ so that they cover the steam ports. The valve 
rod being m position^ and connected to the rocker arms by 
means of the short link, the nut or nuts securing the valve 
to the rod should be so adjusted as to be equidistant from 
the lugs on the valve, say 3^2 or % of an inch, according to 
the amount of lost motion desired, which latter factor 
governs the length ^of stroke in some makes of duplex 
pumps, while in others it is controlled by tappets on the 




Fig. 59 
davis belt driven feed pump 



valve rod outside of the valve chest. Care should be taken 
while making these adjustments that the valve be retained 
exactly in its central position. 

Having set the valves correctly, move one of the pistons 
far enough from mid-stroke to get a small opening of the 
steam port on the opposite side, then replace the valve chest 
covers and the pump will be ready to run. As these valves 



152 Steam Engineering 

are generally made without any outside lap, a slight move- 
ment of one of the pistons in either direction from its 
central position will suffice to uncover one of the ports on 
the other cylinder sufficiently to start the pump. 

Sometimes duplex pumps "work lame/^ that is, one piston 
will make a quick full stroke, while the other piston will 
move very slowly, and just far enough to work the steam 
valve of the opposite side. In the majority of cases this 
irregular action is due to unequal friction in the packing 
of the rods, or the packing rings on one of the pistons may 
be worn out. 

If one side of a duplex pump becomes disabled from any 
cause, as breaking of piston rod in the water cylinder, for 
instance, which is liable to happen, the pump may still be 
operated in the following manner until duplicate parts to 
replace the broken ones have been secured: Loosen the 
nuts or tappets on the valve stem of the broken side and 
place them far enough apart, so that the steam valve will 
be moved through only a small portion of its stroke, thereby 
admitting only steam enough to move the empty steam 
piston and rod, and thus work the steam valve of the re- 
maining side. The packing on the broken rod should be 
screwed up tight, so as to create as much friction as pos- 
sible; there being no resistance in the water end. In this 
way the pump may be operated for several days or weeks 
and thus prevent a shut down. 

Large Boiler Feed Pumps. The plan of using one large 
pump for feeding the boilers has recently been tried in 
several large power stations. For instance, in the Ashley 
Street Power House of the Union Electric Light and Power 
Company of St. Louis, there was recently installed one large 
Prescott steam pump to take the place of four smaller 
ones which had been in use for feeding the boilers. 



Boiler Setting and Equipment 15S 

This pump is of the duplex compound condensing type, 
having high-pressure steam cylinders 18 inches in diameter, 
low-pressure steam cylinders 34 inches in diameter and 
water plungers 17 inches in diameter, with 24-inch stroke in 
each instance. The normal capacity of the pump is 1,800 
gallons per minute, or 900,000 pounds of water per hour, 
which is equal to 45,000 kilowatts at 20 pounds per kilo- 
watt-hour. The present capacity of the Ashley street power 
station is 36,000 kilowatts. 




Fig. 60 
worth ington duplex boiler feed pump 

The novel departure of installing a boiler feed-pump in 
one .large unit for this work will arouse the interest of engi- 
neers, because it is customary to install several small units 
for boiler-feed purposes in power plants of this size. But 
as a matter of fact, this large pump is the consummation 
of a process of evolution in this plant, which was at first 
equipped with several small feed-pumps. 

To produce the most economical results, the low-pressure 
cylinders and their heads are steam- jacketed; the steam 
valves are of the rotative type, there being one steam valve 
for the high-pressure cylinders, and two each for the low- 
pressure cylinders. The arrangement of two steam Valves 

L 



154 



Steam Engineering 



in the low-pressure steam cylinders reduces the clearance 
to the lowest possible amount. The water end is of the pot- 
form type, having four suction and discharge valves, 5% 
inches in diameter, in each quarter of the suction and dis- 
<3harge. The water plungers are of cast bronze of the out- 
side end-packed type. 







Fig. 61 
phantom view of marsh independent steam pump* 

The boiler pressure carried is 175 pounds per square 
inch. The pump operates against a pressure of 225 pounds 
per square inch in the feed- water pipe system to the boilers. 
This feed-water system is provided with a relief valve, and 
the pump is controlled by a pressure governor. The boilers 
are provided with thermostat valves, which allow the water 
to flow into the boilers and maintain the proper level. All |, 
of the automatic apparatus may be controlled by hand. 



Boiler Setting and Equipment 



155 



when desirable, for all the boilers, or for each boiler separ- 
ately. Such occasions are very rare, however, as the pump 
responds readily to changes in station load, and is under 
perfect control of the automatic devices for controlling and 
delivering the proper amount of feed-water to each boiler. 
The feed-pipe system, in effect, is simply a system of 







^^^^^. 



Fig. 62 

the wokthington compound steam pump 

Piston Pattern, for General Service — For 150 Pounds Water 

Pressure 



water mains, in which the number of valves and fittings 
liable to leak are reduced to a minimum. 

Figures 62 and 63 show views of the Worthington boiler 
feed pump, adaptable to large steam plants. In the ar- 
rangement of steam cylinders shown in figure 62, the steam 
is used expansively, thereby effecting a great saving. 



156 Steam Engineering 

Figure 64 illustrates a type of pump which is rapidly 
coming into favor for feeding boilers against high pressure.* 
The steam pressures of from 150 to 200 pounds, which are 
in common use, require a more substantial construction of 
feed-pump than the lower pressures of a few years ago. 
These machines are designed for high pressure and for 
handling either hot or cold water. The steam ends are 
made extra heavy and provided with extra strong bolting 
for all joints, making them suitable for constant operation 
under steam pressures up to 200 pounds per square inch. 
The water ends are of the piston pattern, pot-valve type, 
are of ample strength for working pressures up to 200 
pounds and will easily stand test pressure of 300 pounds 
per square inch. The piston-pattern construction requires 
less room than the outside-packed machine of either the 
center-packed, or end-packed type, and, furthermore, does 
away with the large outside stuffing-boxes and excessive 
amounts of drip. The pistons are fibrous-packed and are 
readily accessible on removal of the cylinder-heads. 

The valves are in special valve chambers or pots, located 
above the cylinders. This arrangement provides for con- 
stant submergence of the pistons, and the reliability of 
action of the machine consequent to such submergence. 
Each pot contains one suction and one discharge valve, each 
valve having an individual cover easily removable for in- 
spection. Valves are of composition of the wing-guided 
type, with bevel seats, and are of ample area for the re- 
quirements of the service. A manifold connects the suction 
openings of the various pots to a common suction inlet and 
another manifold provides a common discharge outlet. 

While designed primarily for boiler-feed purposes, these 
pumps are very desirable machines for general service 



Boiler Setting and Equipment 



157 



against pressures not exceeding 200 pounds per square inch. 
A good engineer will always take a pride in keeping his 
feed pump in good condition^ and if he has two or more 
of them, which every steam plant of any consequence should 
have, he will have an opportunity to keep his pumps in 
good shape. The water pistons of most boiler feed pumps 
are fitted to receive rings of fibrous packing. The best 




Fig. 63 

the worthington packed-plunger pump 

Scranton Pattern — For 250 Pounds Water Pressure 

packing for this purpose and one that will stand both hot 
and cold water service is made of pure canvas cut in strips 
of the required width, ^4, %, % inches, etc., and laid to- 
gether with a water proof cement having the edges for the 
wearing surface. This packing is called square canvas 
packing, and can be purchased in any size required for the 
pump. The size is easily ascertained by placing the water 



158 Steam Engineering 

piston^ minus the follower plate, centrally in the water 
cylinder and measuring the space between the piston and! 




Fig. 64 
deane piston-pattern pot-valve-type boiler feed-pump 

cylinder walls. This packing should not be allowed to 
run for too long a time before renewing, for the reason 
that pieces of it are liable to become loose, and be forced 



Boiler Setting and Equipment 159 

along with the feed water on its way to the boiler and 
lodge under the check valve, holding it open and causing 
no end of trouble. If the feed pump has to handle hot 
water, or has to lift the water several feet by suction, the 
packing rings should be looked after at least once a month. 
Provisions for Testing. While considering feed pipes 
and other apparatus necessarily appertaining to the feeding 
of boilers, it is well to devote a short space also to the fit- 
tings, and other devices required for successfully conducting 
tests of the boiler and furnace. This subject is mentioned 
here for the reason that the author considers that the nec- 
essary fittings and appliances for making evaporative tests 
properly belong to, and in fact are a part of, the feed 
piping, and can be put in while the plant is being erected at 
much less cost and trouble than if the matter is postponed 
until after the plant is in operation. 

Beginning then at the check valve, there should be a 

: tee located in the horizontal section of the feed pipe, as 
near to the check valve as practicable, and between it and 

' the feed pump ; or a tee can be used in place of an ell to 

^connect the vertical and horizontal sections of the branch 
pipe where it rises in front of the boiler. One opening 
of this tee is reduced to % or % inch to permit the attach- 
ment of a hot water thermometer. (See Pig. 65). These 
thermometers are also made angle-shaped at the shank, so 
that if desired they can be screwed into a tee placed in 
vertical pipe, and still allow the scale to stand vertically. 

(The thermometer is for the purpose of showing at what 
temperature the feed water enters the boiler during the 

^ test, and therefore should be as near the boiler as possible. 

^ After the test is completed the thermometer may be taken 

^lout and a plug inserted in its place. 



160 



Steam Engineering 



Fig. 65 
hot water thermometer 



Boiler Setting and Equipment 161 

The next requirement will be a device of some kind for 
ascertaining the weight of water pumped into the boiler 
during the test. In some well ordered plants each boiler is 
fitted with a hot water meter in the feed pipe^ but as this 
arrangement is hardly within the reach of all^ a substitute 
equally as accurate can be made by placing two small water 
tanks^ each having a capacity of eight or ten cubic feet, in 
the vicinity of the feed pump. These tanks can be made 
of light tank iron, and each should be fitted with a nipple 
and valve near the bottom for connection with the suction 
side of the pump. The tops of the tanks may be left open. 
If an open heater is used, and it is possible to place the 
tanks low enough to allow a portion of the water from the 
heater to be led into them by gravity, it will be desirable 
to do so. A pipe leading from the main water supply, with 
a branch to each tank, is also needed for filling them. One 
of the feed pumps, of which there should always be at least 
two, as already stated, is fitted with a tee in the suction pipe 
near the pump to receive the pipe leading from the tanks. 
During the test the main suction leading to this pump 
from the general supply should be kept closed, so that only 
the water that passes through the tanks is used for feeding 
the boiler. If the plant be a small one, with but one or 
two boilers and only a single feed pump, the latter can be 
made to do duty as a testing pump, because during the test 
there will be no other boilers to feed besides the ones under 
test. 

If metal tanks are considered too expensive, two good 
water-tight barrels can be substituted. Figure 6Q will give 
the reader a general idea of what is needed for obtaining the 
weight of the water by the method just described. If a 
closed heater is used and no other boilers are in service dur- 



162 



Steam Engineering 



ing the test, the cold water can be measured in the tanks 
and pumped directly through the heater, but if it is nec- 
essary to feed other boilers besides those under test, then 
either a separate feed pipe must be run to the test boilers, 
or else hot water meters will have to be put into the branch 
pipes. 



f'^^PWnrE. 



%^yy^r£^5i/ppiy 




Toma^UMp 



Fig. 66 



In cases where a separate feed pipe must be put in for 
the test boiler, and the water which is used for testing can- 
not be passed through a heater, there should be a % or 1 
inch pipe connected to the feed main, or header and leading 
to the testing tanks, in order to allow a portion of the hot 
feed water to run into and mix with the cold water in the 
tanks as they are being filled, thus partially warming the 
water before it goes to the boiler. 



Boiler Setting and Equipment 



163 



THE INJECTOR. 



The Injector, Although the injector is not generally 
used for feeding stationary boilers, still a short study of the 




Fig. 67 
original form of the gifford injector 

{philosophy of its action may prove interesting, and useful 
to engineers and water tenders. Consequently a space will 
be devoted to this useful device for boiler feeding. 



164 Steam Engineering 

Ever since the time of the invention of the injector in 
1858 by that eminent French engineer Henri Giffard, and 
its introduction into this country in 1860 by Wm. Sellers 
& Co.^ of Philadelphia^ it has been constantly improved 
upon, and developed by various inventors and manufact- 
urers. 

How an Injector Worlcs, How can an injector lift and 
force large volumes of water into the boiler, against th^ 
same or even higher pressure than that of the steam? 

An injector works because the steam imparts sufficient 
velocity to the water to overcome the pressure of the boiler. 

This is a statement of fact; to explain the action, we 
will take up the important parts of the question separately. 

Why should an injector work? Let us assume that the 
boiler pressure is 180 pounds — that is to say, every square 
inch of the sheets, top and bottom, receives an internal 
pressure of 180 pounds. If the thermometer is placed in- 
side, it is found that both the water and the steam are at 
the same temperature, 379°. But the steam contains more 
heat than the water, because after water is heated, more 
coal must be burned to break up the drops of water to 
change them into steam; this heat is stored in the steam 
and represents work done by the burning of the coal. 
Steam not only exerts a pressure of 180 pounds per square 
inch, but also can expand eight, to twenty-six times its 
original volume, depending upon whether it exhausts into 
the air or into a partial vacuum; water under the same 
pressure would be discharged in a solid jet, and without 
expansion. Either steam, or water can be used in the cylin- 
der of an engine, or to drive the vanes of a steam or water 
turbine, but one pound of steam is capable of much more 
work than one pound-weight of water, on account of the 



Boiler Setting and Equipment 165 

heat which has been used to change it into steam. This is 
easily seen by comparing the velocities of discharge from 
a steam nozzle and a water nozzle under 180 pounds pres- 
sure; steam would expand while issuing^ reaching at the 
end of the nozzle a velocity of about 3^600 feet per second, 
while the water, having no expansion, would have a velocity 
of only 164 feet per second, about 1/22 of that of the 
steam. The same weight of steam discharged per second 
would therefore have vastly more power for doing work 
than the water jet. 

If a steam or water jet comes in contact with a body in 
front of it, the tendency is to drive the body forward. The 
force which tends to move the body is called ^^momentum,^^ 
and is equal to the weight of water or steam discharged by 
the jet in one second, multiplied by its velocity per second. 
If 1 pound of both the water and the steam are discharged 
per second, the ^^momentum^^ of the steam jet is 3,600 ; 
because 1 multiplied by 3,600=3,600; the momentum of 
the water jet is 164. If the water jet discharged about 
22 pounds per second, its momentum would be the same 
as that of the steam, because 22 multiplied by 164 is nearly 
3,600. The two jets are discharged under the same pres- 
sure, but the steam has 22 times as much '^^momentum^^ or 
force as the water jet; it could, therefore, easily enter a 
boiler at 180 pounds pressure if we could reduce it to the 
size of the hole of the water nozzle. 

How ought an injector to work ? Here a practical diffi- 
culty is reached. A steam jet 6 inches from the nozzle is 
much larger than at the opening, and it would appear 
ialmost impossible to make it enter a smaller tube. Even 
lat the narrowest part of the nozzle it is more than sixteen 
Itimes larger in diameter than a water jet discharging the 



i 



166 Steam Engineering 

same weight per second; therefore^ if the steam is changed 
to water without reducing its velocity, it would pass. through 
a hole one-sixteenth the diameter of the ^^steam nozzle^^ at 
a velocity of 3,600 feet per second. The simplest and best 
way to reduce its size is to condense it, and to use water for 
this purpose, especially as water is needed in the boiler. 
To condense the steam and utilize its velocity, the water 
must be brought into close contact with it, without inter- 
fering with the direct line of discharge ; a funnel, or ^^com- 
bining tube^^ suitably placed will compel water to enter 
evenly all around the steam jet. The mouth of this funnel 
must not be too large, or too much water will enter andi 
swamp the jet; if too small, insufficient water will enter to 
condense' the steam. The effect of condensing the steam 
is to reduce the diameter of the jet; therefore the funnel 
or combining tube must be a smooth, converging taper, to 
lead the combined jet of water and condensed steam into the 
smaller hole of the delivery tube. The effect of the im- 
pact of the steam is to give the water its momentum, so 
that a solid stream shall issue from the lower end of the 
tube. Each little drop of entering water is driven ahead 
faster and faster by the vast number of little atoms of 
steam moving hundreds of times as rapidly, until the steam 
and water thoroughly combine into one swiftly-moving 
jet of water and condensed steam, which contracts suffi- 
ciently in diameter to enter the smaller delivery tube. 

Why does the jet enter the boiler? The combined jet 
now passes from the end of the combining tube into the 
delivery tube; why does it enter the boiler? 

If a pipe shaped like a fire-hose nozzle or a ^^delivery 
tube^^ is connected to a tank or boiler carrying 180 pounds, 
the water will issue in a solid jet with a velocity of about 



f 



Boiler Setting and Equipment 167 

164 feet per second; or^ if we could force water into the 
tube at a speed of 164 feet per second at the same part of 
the tubC;, this water would enter and fill up the boiler^ or 
tank against 180 pounds pressure. Therefore to enter the 
boiler the combined jet of water and steam issuing from the 
combining tube must have a velocity of at least 164 feet 
per second. 

Now^ what is the velocity of the combined jet at the 
lower end of the combining tube? If the steam nozzle 
' discharges one pound per second at 3^600 feet velocity, the 
' momentum of the steam is 1 multiplied by 3,600, or 3,600. 
If the vacuum caused by the condensation of the steam 
^ lifts and draws into the combining tube ten pounds of 
water per second at a velocity of forty feet, its momentum 
is 400; and that of the combined jet is 3,600 added to 400, 
or 4,000. The weight of the combined jet is eleven pounds, 
S and at the time of entering the delivery tube its velocity 
ought to be equal to 4,000 divided by 11, or 366 feet per 
second; but as the water and the steam do not meet in 
'precisely the line of discharge there is a loss of momen- 
tum, and the velocity in the delivery tube is only 198 ffeet 
per second. But the jet only needs a velocity of 164 feet to 
enter the boiler, or tank carrying 180 pounds pressure, 
therefore the actual jet in the delivery tube is able to over- 
come a pressure of 206 pounds per square inch, or 26 
pounds above that of the steam, because the velocity of a 
jet of water under a head or pressure of 206 pounds would 
vbe 198 feet per second. This excess is more than sufficient 
to overcome the friction of the delivery piping and the 
resistance of the main check valve. Therefore: 

The action of the injector is due to the high velocity 
with which a jet of steam strikes the water entering the 



168 



Steam Engineering 



combining tube^ imparting to it its momentum, and form- 
ing with it during condensation a continuous jet of smaller 
diameter, having sufficient velocity to overcome the pres- 
sure of the boiler. 

The Sellers Improved Self-acting Injector, Description. 
This injector is simply constructed and contains few operat- 
ing parts. The lever is used in starting only, and the 
water valve for regulation of the delivery. It is self-adjust- 
ing, with fixed nozzle, and restarts automatically. All the 




Fig. 68 
the self-acting injector, class n improved 

valve seats that may need refacing can be removed; the 
body is not subject to wear and will last a lifetime. 

The action is as follows (referring to Fig. 69) : Steam 
from the boiler is admitted to the lifting nozzle by drawing 
the starting iever (33) about one inch, without withdraw- 
ing the plug on the end of the spindle (7) fr6m the central 
part of the steam nozzle (3). Steam then passes through 
the small diagonal-drilled holes and discharges by the out- 
side nozzle, through the upper part of the combining tube 



Boiler Setting and Equipment 169 

(2) and into the overflow chamber, lifts the overflow valve 
(30), and issues from the waste pipe (29). When water is 
lifted the starting lever (33) is drawn back, opening the 
forcing steam nozzle (3), and the full supply of steam dis- 
charges into the combining tube, forcing the water through 
the delivery tube into the boiler pipe. 

At high steam pressure there is a tendency in all in- 
jectors having an overflow to produce a vacuum in the 




Fig. 69 
the self-acting injector, class n improved ' 

SeUers Standard Form 

chamber (25). In the Improved Self- Acting Injector this 
is utilized to draw an additional supply of water into the 
combining tube by opening the inlet valve (42) ; the water 
is forced by the jet into the boiler, increasing the capacity 
about 20 per cent. 

The water-regulating valve (40) is used only to adjust 
the capacity to suit the needs of the boiler. The range is ' 
unusually large. 



170 Steam Engineering 

The cam lever (34) is turned toward the steam pipe to 
prevent the opening of the overflow valve when it is desired 
to use the injector as a heater, or to clean the strainer. The 
joint between the body (25) and the waste-pipe (29) is 
not subject to other pressure than that due to the discharg- 
ing steam and water during starting ; the metal faces should 
be kept clean and the retaining nut (32) screwed up tight. 

To tighten up the gland of the steam spindle, push in the 
starting lever (33) to end of stroke, remove the little nut 
(5) and draw back the lever (33). This frees the cross- 
head (8) and links (15), which can be swung out of the 
way, and the follower (12) tightened on the packing to 
make the gland steam-tight. 

The injector is a reliable boiler feeder, and is in fact 
more economical than the steam pump, because the heat in 
the steam used is all returned to the boiler, excepting the 
losses by radiation. But the disadvantage attending the use 
of the injector is that it will not work well with the feed 
water at a temperature very much in excess of 100° F., 
while a good steam pump, fitted with hard rubber valves, 
will handle water at a temperature as high as 200° or 
208° F., when the water flows to the pump by gravity from 
a heater, or it will raise water from a receiving tank on a 
short suction lift at a temperature of 150° or 160° F. 

STEAM HEADERS AND CONNECTIONS. 

The design, size and location of the main steam header, 
and the connections between it and the boilers is a very 
important problem, and should receive close attention. 

If it was merely a case of uniting all boiler outlets into a 
' common pipe or header, regardless of the strains of expan- 
sion, and ease of pipe fitting, the difficulties would be few. 



Boiler Setting and Equipment 171 

The header should not only be a main for uniting all the 
boilers, but it should also be of sufficient capacity to act as a 
receiver-reservoir to counteract the eflEects of any momen- 
tarily heavy demand for steam which would otherwise tend 
to lift some of the water out of the boilers. The size of 
the header may be determined by the following rule, viz., 
let sectional area of main header equal, or slightly exceed 
the sum of the areas of all boilfer outlets connected with it. 
Take for example a battery of four 72-inch by 18 feet 
horizontal tubular boilers, each having 6-inch outlets. By 
reference to the table of areas and circumferences of circles 
it will he seen that the area of a circle 6 inches in diameter 
equals 28.274. Therefore the combined areas of the four 
outlets is 28.274X4=113 square inches, and reference to 
the table again will show that a 12-inch pipe will be re- 
quired for the header. It is best to have the header of a 
uniform diameter throughout its length, as it will then 
have the greatest storage capacity possible, and the supply 
to the largest engine or steam user should be taken from as 
near the middle of the header as possible. 

The location of the header must be determined by local 
conditions, and by the relative positions of the boilers to the 
engine room, but the header should be so located that all 
valves, joints and connections are easily accessible, and so 
that the valves can be conveniently operated from a fixed 
platform, or from the top of the boilers. It should not be 
necessary to use a movable ladder to control any steam 
valve on the header, as the chances are that the ladder would 
not be in its place in time of emergency or accident. 
Locating the header in front of the boilers over the firing 
I space should be avoided if possible, as any leakage would 
be liable to discomfort the firemen. A good location is 



172 Steam Engineering 

along the top of the boilers near the rear^ the header being 
supported by brick piers built upon the boiler-setting walls. 

All boiler connections should enter the header at the 
top and the outlets should also be taken from the top to 
insure that any water in the header will not be carried over 
to engine^ but will be drained off at the proper place. It is 
not necessary to pitch the header for draining^ provided 
that the drain connection is made close to the point where 
the heaviest draft of steam is taken. If the header is level, 
the movement of the steam toward the heaviest outlet will 
naturally cause the water in the bottom of the header to 
flow in the same direction. A good arrangement for drain- 
ing a header is to use a cross at the heaviest outlet, with 
the outlet connection taken from the top opening, and the 
lower opening fitted with a blind flange tapped for drain- 
age, but the use of a good high-pressure trap attached to 
the drain opening of the header, and discharging into a 
return tank, hot-well,- or open heater is the most reliable 
method of drainage. 

Valves. The question of valves is next in order. The 
day of the single valve in each boiler connection is passing. 
Many cities by ordinance now require two valves in each 
connection, and many engineers know only too well what it 
means to crawl into a boiler with a leaky valve on top of 
them. This condition can be eliminated by the use of two 
valves. Globe valves should be avoided on account of the 
turns in the- steam path, gate and angle valves being pref- 
erable. One of the neatest, and most efficient arrange- 
ments is to use two angle valves, one on top of the header 
and the other on top of the boiler. 

Automatic stop and check-valves are daily finding favor, 
v.ta\ are coming into general use. These valves which are 



Boiler Setting and Equipment 173 

adaptations of the ordinary check-valve, are generally made 
in tfie angle type to set over the boiler outlet. The disk 
falls to its seat when the flow of steam reverses, so that if 
a tube should blow out the automatic stop and check, or 
non-return valve would close because of the unbalanced 
pressure, thereby isolating the disabled boiler from the 
others. The advantages of such an arrangement are fully 
apparent. The check disk in these valves is not attached 
to the valve-stem, but the valve can be used as an ordinary 
stop-valve by screwing the stem down until it holds the 
disk securely on its seat. It is impossible to open this type 
of valve when the boiler is out of commission, and this in 
itself is a safety item to be considered by those who have 
to enter boilers for cleaning or repairs. The non-return 
valve will also close if the boiler becomes sluggish in gen- 
erating steam, and will not open until the pressure equals 
that in the header. The valve should be equipped with an 
outside lever, or indicating device which will clearly show 
whether it is open or closed. 

There are a few types of non-return valve which have an 
added feature of closing if the velocity should increase in 
the regular direction beyond the normal rate, which might 
easily be caused by the bursting of a pipe or joint in the 
piping system. The location of the automatic stop and 
check-valves should be as near as possible to the boiler 
outlets. Where the ordinary angle or gate valves are used, 
they should preferably have rising stems to readily indicate 
whether the valve is open or closed. 

Superheaters. The location of the superheater in the 
boiler setting is a very important point, but there are cer- 
tain rules and reasons that help to determine where it 
should be placed in a particular type of boiler. The tem- 



174 Steam Engineering 

perature of superheated steam at 150 pounds pressure super- 
heated 200 degrees is 566 degrees^ and if it were desired 
to place a superheater in a boiler to meet such conditions^ 
it is evident that if the temperature of the escaping gases 
were 500 degrees it would be impossible to place the super- 
heater near the uptake. It would be necessary to place the 
superheater at some point in the setting where there would 
be a sufficient temperature drop between the gases and the 
superheating surface to cause the necessary heat transfer. 
The nearer the furnace^ the greater will be the temperature 
drop from the gases to the steam^ and a greater heat trans- 
fer per square foot of heating surface per hour. Therefore, 
for a given degree of superheat the superheater that is 
placed closest to the furnace will require the least heating 
surface per horse-power^ and for a given design the super- 
heater having the least heating surface is the cheapest to 
build. 

If the superheater is placed at such a point in the setting 
that the gases exceed 1^000 degrees^ it is necessary to pro- 
vide for flooding with water whenever the flow of steam 
through the superheater is stopped or during the raising 
of steam. Except in cei;tain special cases flooding is objec- 
tionable, and the superheater should be placed just beyond 
the point where the average temperature of the gases has 
reached 1,000 degrees. In the average water-tube boiler 
having a furnace temperature of 2,500 degrees, and an up- 
take temperature of 500 degrees, 75 per cent of the total 
amount of steam has been generated when the gases have 
passed over 40 per cent of the heating surface and have 
dropped to a little less than 1,000 degrees. 

Besides the above there are other considerations, such as 
adaptability to the design of the boiler, and accessibility 
for cleaning and repairs. 



Boiler Setting and Equipment 3 75 

The superheater contained within the boiler setting is 
the most efKcient type for degrees of superheat not exceed- 
ing 200. It has the added advantage that it does not require 
any additional space for its installation^ except in some cases 
an increase in the height of the boiler. It can be installed 
without any additional piping over that required for a 
simple boiler. If properly located it will deliver a fairly 
uniform temperature of steam, and will automatically fol- 
low the fluctuations in the boiler load. Whenever it is 
necessary to cut out a superheater, only one unit is lost and 
the other units will take care of the loss by carrying an 
overload., thus preventing any wide temperature change in 
the piping system, or an appreciable loss in economy. 

In the boiler-setting type, the superheater is forced when- 
ever the boiler is forced, but the temperature of the escaping 
steam may fluctuate on account of leaving the fire doors 
open too long, or firing too heavily or irregularly. Where 
there are a number of boilers in a battery the temperature 
of the steam at the engines should not vary, as the fluctua- 
tions in temperature do not occur at the same time in all 
the boilers, and therefore the average of all the boilers should 
be nearly constant. Superheaters of this type can be de- 
signed so that they will compound on overload; that is, 
the degree of superheat will increase with the load up 
to a certain amount. 

The freedom of expansion of each of the elements of 
heating surface is very important and should be given care- 
ful consideration. The U-bend provides absolute freedom, 
and cannot produce any strain on the joints, provided its 
movement is not restrained by hangers, or clamps. In de- 
signs where straight or slightly curved tubes are expanded 
at each end into manifolds, considerable trouble is experi- 



176 Steam Engineering 

enced with leaky joints due to the difference in expansion 
of the tubes and the rigidity of the manifolds. 

In properly designed all-steel superheaters very few re- 
pairs will be required^ but just as careful provisions should 
be made for such repairs as if they were of frequent occur- 
rence. All the expanded joints^ and all the manifold cover- 
plates should be easily accessible for inspection and repairs. 

HYDRAULICS FOU ENGINEERS. 

Among the many difficult problems that are continually 
coming up for engineers to solve^ there is none more per- 
plexing than the correct calculation of the quantity of 
water which will be discharged in a given time from pipes 
of various sizes^ and under the many different heads or 
pressures. Problems in hydraulics^ as given by the majority 
of writers on engineerings are usually in elaborate algebraic 
equations;, which^ to the ordinary working engineer^ are 
very perplexing^ at least the author has found them to be so 
in his experience. Therefore with a view of assisting his 
brother engineers in the solution of problems along this 
line which they may be called upon to solve^ the author has 
spent considerable time and labor in searching for and 
compiling a few rules and examples for hydraulic calcula- 
tions in plain arithmetic^ which he hopes may be of benefit. 

First, to find velocity of flow in the pump, or in other 
words, piston speed. 

Rule. Multiply number of strokes per minute by length 
of stroke in feet, or fractions thereof. 

Second, the velocity of flow in the discharge pipe is in 
inverse ratio to the squares of the diameters of the pipe, 
?ind thp water cylinder of pump. 



Boiler Setting and Equipment 177 

ThuS;, a pump cylinder is 6 inches in diameter^ and the 
piston speed is 100 feet per minute; the discharge pipe 
being 3 inches in diameter. What is the velocity of flow 
in the pipe ? 

Example, -r— — r-^4. In this case the velocity in tlie 

pipe is four times that in the pump^ and 100X4=400 feet 
per minutC;, velocity for water in the discharge pipe. 

Thirds to find velocity in feet per minute necessary to 
discharge a given quantity of water in a given time. 

Bule. Multiply the number of cubic feet to be dis- 
chai'ged by 144 and divide by area of pipe in inches. 

Fourth^ to find area of pipe when the volume and velocity 
of water to be discharged are known. 

Rule, Multiply volume in cubic feet by 144 and divide 
by the velocity in feet per minute. 

Fifth^ one of the first requisites in making correct calcu- 
lations of the quantity of water discharged from any sized 
pipe is to obtain the velocity of flow per second. There 
are several rules for doing this^ among which the following 
appear to be the plainest and most simple : 

Rule 1. Multiply the square root of the head in inches 
by the constant 27.8. For instance^ assume the head to be 
100 feet=l,200 inches. The square root of 1,200 is 35 
nearly^ then 35X^'^. 8=973 inches=81 feet per second 
velocity. 

Rule 2. Multiply the square root of the head in feet by 
the constant 8^ as follows: The square of 100=:10 and 
10X8=:80 feet velocity per second. 

Rule 3. Multiply twice the acceleration of gravity by the 
head in feet^, and extract the square root of product. The 



178 Steam Engineering 

acceleration of gravity may be considered the constant num- 
ber 32, neglecting decimals, 32X^X100=6,400. Square 
root of 6,400=80 feet per second. 

In many instances it is more convenient to use the 
pressure in pounds per square inch as shown by gauge, in- 
stead of the height or head, and we can then apply Eule 4. 

Rule 4. Multiply the square root of the pressure in 
pounds per square inch by the constant number 12.16 as 
follows : Pressure due to 100-foot head=44 pounds, nearly. 
Square root of 44=6.6, which multiplied by 12.16=80.2 
feet velocity per second. 

Having ascertained the velocity of flow, we may now 
proceed to calculate the weight of water in pounds per sec- 
ond discharged from any size of pipe, neglecting for the 
time being the loss in pressure caused by friction from 
elbows and bends in the pipe and also the peculiar shape 
assumed by a stream of water flowing through pipes, or 
conduits when there is no resistance except the pressure of 
the atmosphere, and friction caused by long distance trans- 
mission. 

We will take for our calculation a four-inch pipe from 
which the water has a free flow under a head of 100 feet, 
which gives a velocity of 80 feet per second. 

Rule 5. Divide the velocity in feet per second by the 
constant 2.3, and multiply the quotient by the area of dis- 
charge pipe in square inches. 80^-2. 3=:34.7. Now the 
area of a four-inch pipe is 12.57 square inches, and 34.7 
X1^.57=:436 pounds discharge per second. 

In order to get the matter clearly before us, let us assume 
that we have a section of four-inch pipe just 80 feet in 
length and that it lies in a horizontal position and is filled 
solidly full of water. It will contain area, 12.57 square 



Boiler Setting and Equipment 179 

•inches X lengthy 960 inches=12,067.2 cubic inches of water, 
and as one pound of water occupies a space of 27.7 cubic 
inches, we therefore have 12,067.2-f-27.7==436 pounds of 
water, and at a velocity of 80 feet per second our pipe will 
be emptied and refilled continuously each second. We 
have also Eule 6 to find the number of cubic feet dis- 
charged per minute when the velocity per minute is known. 

Rule 6, Multiply the area of pipe in square inches by 
the velocity in feet per minute and divide by the constant 
144. • 

Example. Area of 4-inch pipe=12.57 square inches. 
Velocity of flow=80 feet per second=4,800 feet per min- 
ute. 

Then — - — ^Vr -=419 cubic feet per minute=6.99 cubic 

144 ^ 

feet per second, which multiplied by 62.3 pounds (weight 
of 1 cubic foot)=:435.4 pounds per second. 

As stated before, no allowance is made by the above rules 
for friction or other retarding influences, but for ordinary 
purposes in connection with a steam plant a deduction of 
25 per cent is probably sufficient. Of course if the water is 
being discharged into an elevated tank, or against direct 
pressure of any kind, the resistance in pounds per square 
inch or, the height in feet must be deducted from the im- 
pelling pressure or head. Let us assume, for instance, that 
our 4 inch pipe is discharging water into a tank at an ele- 
vation of 75 feet above the level of the pump, and that to 
reach the tank requires 100 feet of pipe with two 90° ells 
and one straight-way valve. We wish to discharge 500 
gallons per minute into the tank, and will therefore require 
a velocity of about 13 feet per second, which will necessitate 



180 Steam Engineering 

a pressure of a little more than 1 pound per square inch to 
be maintained at the pump over and above all resistance. 
Kow the resistance to be overcome in this case will be : 
Pressure per square inch due to 75-foot head. . . .32.5 IbSo 
Friction loss due to length of pipe and velocity. . . 7.43 lbs. 

Friction loss due to two 90° ells 2.16 lbs. 

Friction loss due to straight-way valve 2 lbs. 



Total 20.19 lbs. 

Consequently the pressure required at the pump will be 
about 22 pounds per square inch^, equal to a head of 50 feet. 



Total 42.29 lbs. 

Eequiring a pressure of say 43 pounds per square inch, or 
about the equivalent of 100 feet head at the pump. 

Again, suppose that in place of the elevated tank we i 
have 1,000 feet of 8-inch horizontal pipe with a 4-inch 
delivery at the end farthest from the pump, and three 
branch pipes each 100 feet long and 4 inches in diameter 
with one 90° ell, one straightway valve, connected at in- 
tervals to the 8-inch main, and it is required to discharge in 
all 1,000 gallons per minute, or at the rate of 250 gallons 
per minute for each 4-inch delivery. The friction loss for 
each 100 feet in length of 8-inch pipe at a velocity of 13 
feet per second is .94 pounds, and for each 100 feet of 4-inch 
pipe it is 1.89 pounds. Likewise the friction loss for each 
90° _ell is 1.08 pounds, and for a straight-way valve .2 
pounds, at the above velocity. The total resistance there- 
fore to be overcome is as follows: 
For 1,000 feet of 8-inch pipe.... .94 lbs. X 10= 9.4 lbs. 

For 300 feet of 4-inch pipe 1.89 Ibs.X 3= 5.67 lbs. 

For four 90° ells 1.08 Ibs.X 4= 4.32 lbs. 

For four straight-way valves 2 Ibs.X 4^ .8 lbs. 



Boiler Setting and Equipment 



181 



Table 13 
pressure of water. 

The pressure of water in pounds per square inch for every foot in height 
to 260 feet; and then by intervals to 3,000 feet head. By this table, from 
the pounds pressure per square inch, the feet head is readily obtained ; and 
vice versa. 





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1 


0.43 


64 


27.72 


127 


55.01 


190 


82.30 


253 


a09.59 


2 


0.86 


65 


28.15 


128 


55.54 


191 


82.63 


254 


110.03 


3 


1.30 


66 


28.58 


129 


55.88 


192 


83.17 


255 


110.46 


4 


1.73 


67 


29.02 


130 


56.31 


193 


83.60 


256 


110.89 


5 


2.16 


68 


29.45 


131 


56.74 


194 


84.03 


257 


111.32 


6 


2.59 


69 


29.88 


132 


57.18 


195 


84.46 


258 


111.76 


7 


3.03 


70 


30.32 


133 


57.61 


196 


84.80 


259 


112.19 


8 


3.46 


71 


30.75 


134 


58.04 


197 


85.33 


260 


112.62 


9 


3.89 


72 


31.18 


135 


58.48 


198 


85.76 


261 


113.06 


10 


4.33 


73 


31.62 


136 


58.91 


199 


86.20 


262 


113.49 


11 


4.76 


74 


32.05 


137 


59.34 


200 


86.63 


270 


116.96 


12 


5.20 


75 


32.48 


138 


59.77 


201 


87.07 


275 


119.12 


13 


5.63 


76 


32.92 


139 


60.21 


202 


87.50 


280 


121.29 


14 


6.06 


77 


83.35 


140 


60.64 


203 


87.93 


285 


123.45 


15 


6.49 


78 


33.78 


141 


61.07 


204 


88.36 


290 


125.62 


16 


6.93 


79 


34.21 


142 


61.51 


205 


88.80 


295 


127.78 


17 


7.36 


80 


34.65 


143 


61.94 


206 


89.21 


300 


129.95 


18 


7.79 


81 


35.08 


144 


62.37 


207 


89.66 


305 


132.12 


19 


8.22 


82 


35.52 


145 


62.81 


208 


90.10 


310 


134.28 


20 


8.66 


83 


35.95 


146 


63.24 


209 


90.53 


315 


136.46 


21 


9.09 


84 


36.39 


147 


63.67 


210 


90.96 


320 


138.62 


22 


9.53 


85 


36.82 


148 


64.10 


211 


91.39 


325 


140.79 


23 


9.96 


86 


37.25 


149 


64.54 


212 


91.83 


330 


142.95 


24 


10.39 


87 


37.68 


150 


64.97 


213 


92.20 


335 


145.12 


25 


10.82 


88 


38.12 


151 


65.40 


214 


92.69 


340 


147.28 


26 


11.20 


89 


38.55 


152 


65.84 


215 


93.13 


345 


149.45 


27 


11.69 


90 


38.98 


153 


66.27 


216 


93.56 


350 


151.61 


28 


12.12 


91 


39.42 


154 


66.70 


217 


93.99 


355 


153.78 


29 


12.55 


92 


39.85 


155 


67.14 


218 


94.43 


360 


155.94 


30 


12.99 


93 


40.28 


156 


67.57 


219 


94.86 


.365 


158.10 


31 


13.42 


94 


40.72 


157 


68.00 


220 


95.30 


370 


160.27 


32 


13.86 


95 


41.15 


158 


68.43 


221 


95.73 


375 


162.45 


33 


14.29 


96 


41.58 


159 


68.89 


222 


96.16 


380 


164.61 


34 


14.72 


97 


42.01 


160 


69.31 


223 


96.60 


385 


166.78 


35 


15.16 


98 


42.45 


161 


69.74 


224 


97.03 


390 


168.94 


36 


15.59 


99 


42.88 


162 


70.17 


225 


97.46 


395 


171.11 


37 


16.02 


100 


43.31 


163 


70.61 


226 


97.90 


400 


173.27 


38 


16.45 


101 


43.75 


164 


71.04 


227 


98.33 


425 


184.10 


39 


16.89 


102 


44.18 


165 


71.47 


228 


98.76 


450 


195.00 


40 


17.32 


103 


44.61 


166 


71.91 


229 


99.20 


475 


205.77 


41 


17.75 


104 


45.05 


167 


72.34 


230 


99.63 


500 


216.58 


42 


18.19 


105 


45.48 


168 


72.77 


231 


100.00 


525 


227.42 


43 


18.62 


106 


45.91 


169 


73.20 


232 


100.49 


550 


238.25 


44 


19.05 


107 


46.34 


170 


73.64 


233 


100.93 


575 


249.09 


45 


19.49 


108 


46.78 


171 


74.07 


234 


101.39 


600 


259.90 


46 


19.92 


109 


47.21 


172 


74.50 


235 


101.79 


625 


270.73 


47 


20.35 


110 


47.64 


173 


74.94 


236 


102.23 


650 


281.56 



182 



Steam Engineering 
Table 13 — continued. 





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(L) 


o; 


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fe 


Ph 


fe 




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1-1 

Ph 


fe 


Plh 


48 


20.79 


111 


48.08 


174 


75.37 


237 


102.66 


675 


292.40 


49 


21.22 


112 


48.51 


175 


75.80 


238 


103.09 


700 


303.22 


50 


21.65 


113 


48.94 


176 


76.23 


239 


103.53 


725 


314.05 


51 


22.09 


114 


49.38 


177 


76.67 


240 


103.96 


750 


324.88 


52 


22.52 


115 


49.81 


178 


77.10 


241 


104.39 


775 


335.72 


53 


22.95 


116 


50.24 


179 


77.53 


242 


104.83 


800 


346.54 


54 


23.39 


117 


50.68 


180 


77.97 


243 


105.26 


825 


357.37 


55 


23.82 


118 


51.11 


181 


78.40 


244 


±05.96 


850 


368.20 


56 


24.26 


119 


51.54 


182 


78.84 


245 


106.13 


875 


379.03 


57 


24.69 


120 


51.98 


183 


79.27 


246 


106.56 


900 


389.86 


58 


25.12 


121 


52.41 


184 


79.70 


247 


106.99 


925 


400.70 


59 


25.55 


122 


52.84 


185 


80.14 


248 


107.43 


950 


411.54 


60 


25.99 


123 


53.28 


186 


80.57 


249 


107.85 


975 


422.35 


61 


26.42 


124 


53.71 


187 


81.00 


250 


108.20 


1000 


433.18 


62 


26.85 


125 


54.15 


188 


81.43 


251 


108.73 


1500 


649.70 


63 


27.29 


126 


54.58 


189 


81.87 


252 


109.16 


2000 
3000 


866.30 
1,299.50 



QUESTIONS AND ANSWERS. 

111. What two methods of support are generally used 
in the setting of horizontal tubular boilers ? 

Ans. First: By suspension from I beams and girders, 
and secondly by means of brackets riveted to the side sheets, 
and resting upon the side walls. 

112. How are water tube boilers usually supported in 
the setting? 

Ans. By suspension. 

113. What important details should be looked after 
concerning the brick work? 

Ans. The foundations should be good, and the walls 
built in such manner as to take care of the expansion and 
contraction. 

114. How is this accomplished? 



Questions and Answers 183 

Ans. By leaving an air space of two inches in the side 
and rear walls beginning at the level of the grate bars^ and 
extending up to about the center line of the boiler. 

115. What kind of brick should be used for inside 
lining ? 

Ans. Fire brick of good quality. 

116. How should bridge walls be built for horizontal 
tubular boilers ? 

Ans. Straight across from wall to wall. 

117. About what distance from the bottom of the boiler 
should this wall be ? 

Ans. Eight to ten inches. 

118. Where is the combustion chamber? 
Ans. It is the space back of the bridge wall. 

119. How should boiler walls be secured? 

Ans. By means of tie rods extending the entire length, 
and breadth of the setting. 

120. What are the buck stays? 

Ans, They are strong cast-iron, or wrought-iron bars 
placed vertically upon the outside of the walls, and secured 
to the tie rods. 

121. Should horizontal tubular boilers be set perfectly 
level lengthwise? 

Ans. It is better that they be set about one inch lower 
at the back end, than at the front end. 

122. Give one of the main reasons for this style of 
setting. 

Ans. When washing out the boiler, the mud and water 
will more easily drain towards the blow off pipe. 

123. What is the usual ratio of grate surface to heating 
surface ? 



184 Steam Engineering 

Ans. One square foot of grate surface to each 36 square 
feet of heating surface. 

124. At what point should the glass water-gauge be 
located ? 

Ans. In such a position as to bring the lowest visible 
portion of the gauge glass exactly on a level with the top of 
the upper row of tubes of a horizontal tubular boiler. With 
other types of boilers the lowest end of the gauge glass 
should always be on a level with the danger point. 

125. Whj should the above rules be observed in locating 
a water column? 

Ans. Because when the Avater level in the glass begins 
to draw near to the lower end of glass the engineer or water 
tender will have an infallible guide to warn him to get 
busy. 

126. What is a good indication that the connections of 
the water glass are choked or plugged with scale? 

Ans. When there is no movement of the water in the 
glass. 

127. Why should there be a trap/ or siphon in the pipe 
connecting the steam gauge to the boiler? 

Ans. To prevent the hot steam from coming into eon- 
tact with the spring of the gauge. 

128. How may the steam gauge^ and safety valve be 
tested in comparison with each other? 

Ans. By occasionally raising the steam pressure high 
enough to cause the valve to open at the point for which 
it is set to blow. 

129. Is the pop valve reliable as a safety valve? 

Ans. It is, if not allowed to stand idle too long and 
become rusty. 

130. How often should it be allowed to blow off? 



Questions and Answers 185 

Ans. At least twice a week. 

131. Are lever safety valves used to any extent? 

Ans, They are still in use to some extent^ but are rapidly 
being superseded by pop valves. 

132. What is the function of a fusible plug? 

Ans, The fusible alloy of which it is coraposed will melt 
when it comes in contact with dry steam^ and allow the 
steam to blow a warning. 

133. Where is the fusible plug located? 

Ans, In that portion of the heating surface of a boiler 
which is first liable to be overheated from lack of water. 

134. Are Domes and Mud drums necessary parts of 
boilers ? 

Ans, They are not as a rule. 

135. Where should the hlo\y off pipe always be con- 
nected ? 

Ans, With the lowest part of the water space. 

136. Should the blow off cock be opened while the 
boiler is under pressure ? 

Ans, Yes^ for a few seconds^ once^ or twice each day. 

137. Is a surface blow ofl any advantage? 
Ans, It is, especially if the water is muddy. 

138. What precautions should be observed with regard 
to inlet for feed water? 

Ans, The feed water should not be allowed to come 
directly in contact with the hot boiler sheets until its 
temperature is equal to, or near that of the water within 
the boiler. ' 

139. How may this be brought about? 

.4ns. By means of feed water heaters, and internal coil? 
of pipe through which the feed water is caused to pass. 

140. What is the most economical style of feed pump? 



186 Steam Engineering 

Ans, The belt-driven power pump. 

141. Is it the most reliable^ or safest? 
Ans, It is not. 

142. What is the most reliable boiler feeding device, for 
all conditions of stationary practice? 

Ans. The double acting steam pump. 

143. What precautions should be observed in figuring 
on the capacity of a feed pump for a battery of two or 
more boilers? 

Ans. To take into account the total quantity of water 
required by all of the boilers ; and let the capacity of the 
pump be equal to it, 

144. In connection with feed apparatus for boilers, 
what other fittings and devices should be installed? 

Ans. There should be a tee located in the horizontal 
section of the feed pipe near the check valve, and between it 
and the feed pump. One opening of this tee is to be re- 
duced to % or 1/^ inch to receive a hot water thermometer 
for testing the temperature of the feed water when making 
evaporative tests, etc. 

145. What other provisions along this line should be 
made ? 

Ans. Tanks for weighing the feed water — also a sep- 
arate feed pipe to the boiler under test, also means for 
weighing the coal burned during test. 

146. Is the injector an efficient boiler feeder? 

Ans. It is in locations where there is not very much 
exhaust steam available for heating the feed water. 

147. When, and by whom was the injector invented ? 
Ans. In the year 1858, by Henri Giffard. 

148. Why does an injector force water into a boiler 
that is under steam pressure? 



Questions and Answers 187 

Ans, Because the steam passing through the injector 
imparts sufficient velocity to the water to overcome the 
boiler pressure. 

149. Why does an injector lift water from a lower level ? 

Ans, Because the condensation of the steam in the com- 
bining tube creates a vacuum there^ and in the suction 
pipe connected with it. 

150. How may the size of the steam header for a battery 
of boilers be determined? 

Ans. The sectional area of the header should equal or 
slightly exceed the sum of the areas of all the boiler outlets 
to be connected with it. 

151. Where should all connections except for drainage, 
enter, and leave the main header? 

Ans. At the top. 

152. How many valves should there be in each boiler 
connection leading to the header ? 

Ans. Never less than two. 

153. What kind of valves are best for this purpose? 
Ans. Automatic stop, and check valves. 

154. What is the most efficient type of superheater for 
practical purposes? 

Ans. The one that is contained within the boiler setting. 

155. How is the velocity of flow, or piston speed per 
minute of a pump ascertained? 

Ans. Multiply number of strokes per minute by length 
of stroke in feet, or fractions thereof. 

156. The piston speed being known, how is the velocity 
oi flow in the discharge pipe found? 

Ans. The velocity of flow in the discharge pipe is in 
inverse ratio to the squares of the diameters of the pipe and 
the water cylinder of pump. 



188 Steam Engineering 

157. When it is required to discharge a certain quantity 
of water from a given size of pipe in a given time^ how 
may the velocity of flow in feet per minute be found? 

Ans. Multiply the number of cubic feet to be discharged 
by 144 and divide by area of pipe in inches. 

158. When the volume of watet to be discharged and 
the velocity of flow are loiown^ how is the area of the pipe 
obtained ? 

Ans. Multiply volume in cubic feet by 144^ and divide 
by velocity in feet per minute. 

159. What is meant by "acceleration of gravity/' and 
what constant number represents it in connection with 
hydraulics ? 

A71S. Acceleration of gravity is the increase in velocity 
caused by the actual weight of the water^ and is represented 
by the constant 32. 

160. What per cent of allowance is ordinarily made for 
friction in water pipes? 

Ans, A deduction of 25 per cent is sufficient. 



Feed Water Heaters 



Feed Water Heaters. One great source of economy in 
fuel is the utilization of all the available exhaust steam for 





Fig. 70 

baragwanath steam jacket 

feed water heater 



Fig. 71 
interior view of open 

HEATER 



heating the feed water before it enters the boiler. Of 
course if the main engines are condensing, the exhaust from 

189 



190 Steam Engineering 

that source is not directly available^ except by interposing 
a closed heater between the cylinder and the condenser, 
or by using the water of condensation for feeding the 
boilers. This can be done with safety, provided a surface 
condenser is used^ but with a jet condenser or an open 
heater in which the exhaust mingles with the water, it is 
advisable to have an oil separator to prevent the oil from 
getting into the boilers. 

Exhaust heaters are of two kinds, open and closed. In 
the open heater the exhaust steam mingles directly with 
, the water, and a portion of it is condensed. A well-designed 
open exhaust heater will raise the temperature of the water 
to very nearly the boiling point, 212° F. These heaters 
should be set eo that the water will flow by gravity from 
them to the feed pump. In the closed type of exhaust 
heaters the exhaust steam and the water are kept separate. 
In some styles the steam passes through tubes, which are 
surrounded by water, while in others the water fills the 
tubes, which are in turn surrounded by the steam. In 
either case the water in the closed heater is under the full 
boiler pressure, while the feed pump is in operation, be- 
cause the heater is between the pump and the boiler, while 
with the open heater the pump is between the heater and 
the boiler. 

The saving effected by heating the feed water with ex- 
haust steam can be easily ascertained by the use of a 
thermometer, a steam table, and a simple arithmetical cal- 
culation. First, find by thermometer the temperature of 
the water before entering the heater; find its temperature 
as it leaves the heater. Next ascertain by table 17 the 
number of heat units above 32° F. in the water at each of 
the two temperatures. Subtract the less from the greater. 



i 




Fig. 72 



192 Steam Engineering 

and the remainder will be the number of heat units added 
to the water by the heater. Next find by table 17 the num- 
ber of heat units above 32 °F. in the steam at the pressure 
ordinarily carried in the boiler^ and subtract from this the 
number of heat units in the water before it enters the 
heater. The result will be the number of heat units that 
would be required to convert the water into steam of the 
required pressure^ provided no heater were used. Then to 
find the percentage of saving effected by the heater, multi- 
ply the number of heat units added to the water by the 
heater by 100, and divide by the number of heat units re- 
quired to convert the unheated water into steam, from the 
initial temperature at which it enters the heater. 

Example. Assume the boiler to be carrying 100 pounds 
gauge pressure. Suppose the temperature of the water 
before entering the heater is 60° F., and that after leaving 
the heater its temperature is 202° F., what is the percentage 
of saving due to the heater ? The solution of the problem 
is as follows: 

Boiler pressure by gauge=100 pounds. 

Initial temperature of feed water:=60° F. 

Heated temperature of feed water=202° F. 

From Table 17 it is found that 

Heat units in water at 202° F.=170.7. 

Heat unit in water at 60° F.=28.01. 

Heat units added to water by heater=170.7 — 28.01= 
142.69. 

Heat units in steam at 100 pounds gauge pressure^ 
1185.0. 

Heat units to be added to water at 60° F. to make steam 
of 100 pounds gauge pressure=1185.0— 28.01=1156.99. 



Feed Water Heaters ,193 

Percentage of saving effected by the u-se of the heater 
142.69X100 



1156.99 



- = 12.33 per cent. 



Suppose the coal consumed under this boiler amounts to 
two tons per day at a cost of $3.00 per ton^ or a fuel cost 
of $6.00 per day. Then the saving in dollars and cents due 
to the heater in the foregoing example would be 12.33 per 
cent of $6.00, or $0.7398 (74 cents) per day. 

Hoppes Class R Heater. Figure 74 is a side sectional 
elevation of a Hoppes class E open feed-water heater, Fig. 
75 being an end sectional view of the same. Although this ' 
heater has been on the market several years, it has recently 
been improved, and embodies features not hertof ore shown. 
The shell of the heater is cylindrical and the heads are 
^^bumped,^^ a design calculated to resist pressure, and also 
to prevent pulsations due to the impulses of the exhaust. 
The interior of the heater is provided with layers of trough- 
shaped pans arranged in tiers and designed to afford a 
large amount of heating surface. To avoid corrosion the 
pans are of cast-iron, as are also the bottom of the shell, 
the lower ends of the center posts, and all other parts with 
which the water comes in contact. The shell may be en- 
tirely cast-iron, however, if desired. In the back end of the * 
heater is located a large oil catcher, through which the ex- 
haust passes. See Fig. 74. 

The principle of operation is, to provide that the flow of 
water from the cast-iron troughs at the top be so gradual 
that the water will be distributed over the edges of the 
pans in a thin film, and over the sides and ends so gently 
that it will, follow the bottom contour of each pan to the 
lowest point before dropping oft' into the pan beneath. 



194 



Steam Engineering 




Fig. 73 
closed feed water heatee 



While the water is following the under side of the pans, 
the exhaust steam will come in direct contact with, and heat 



Feed Water Heaters 



195 



it to the temperature of the exhaust. Lime and other solids 
which may be held in solution in the water will, when 
liberated by the heat, form mostly on the under side of the 
pans and hence will not detract from the efficiency of the 
process, as the same direct action of the exhaust on the 
water will continue as when the pans are clean. 

In open heaters of large size the regulation and 
distribution of water so as to obtain the best results are im- 





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Fig. 74 
sectional elevation of hoppes class r feed-water heater 

portant. In the Hoppes apparatus the water is regulated 
to the heater by a. float in a separate float-chamber operat- 
ing a double-disk balanced valve of the company^s manu- 
facture. Branch pipes from the main feed-pipe are con- 
nected to the shell at the top, and these branches have ex- 
tensions inside the heater to which are attached flanged 
tees. To the flanges of these tees are bolted flanged inverted 
IL-shaped pipes, the long arms of which extend below the 
iwater level of the feed troughs in the top of the heater. 



196 



Steam Engineering 



Disks with orifices of proper and equal size are placed be- 
tween the flanges of the L-shaped feed-pipes and the tees, 
and by this means the water is equally distributed into the 
various tiers of pans. 

When it is desired to feed two or more heaters in multiple, 
an equal distribution of water is given to all the heaters 
by using a single regulating valve on the main water inlet, 
and branching the same to the heaters to be supplied. 




Fig. 75 
end sectional view of hoppes class r heater 

A feature recently added is an overflow dam, at the rear 
end of the heater, which is intended to act as a skimmer 
and also to add to the capacity of the overflow pipe by in- 
creasing the head on the outlet without causing the water 
to rise higher in the heater. The drip from the oil separator 
is piped into the chamber formed by the dam, but this may 



Feed Water Heaters 197 

have a separate connection^ if prefeired. Filters are pro- 
vided on request^ but it is believed that the large amount 
of lime-catching surfaces obviates the necessity for their 
use in most cases. 

These heaters are built in sizes ranging from 50 to 
30^000 horse-power. 

Heaters^ especially those of the closed type^ should have 
capacity sufficient to supply the boiler for fifteen or twenty 
minutes. There would then be a body of water continually 
in the heater in direct contact with the heating surface, and 
as it passes slowly through it will receive much more heat 
than if rushed through a heater that is too small. All 
heaters and feed pipes should be well protected by some 
good insulating covering to prevent loss of heat by radia- 
tion. In some cases the exhaust steam, or a portion of it at 
least, can be used to advantage in an exhaust injector. This 
device, where it can be used at all, is economical in that it 
not only feeds the boiler, but also heats the water without 
the use of live steam. But it will not force the water against 
a pressure much above 75 pounds to the square inch, and 
if the initial temperature of the water is much above 75° P. 
the exhaust injector will not handle it. Heaters which use 
live steam direct from the boilers heat the feed water to a 
much higher temperature, so that they act as purifiers by 
removing a large portion of the scale-forming impurities 
before the water enters the boiler. ' Live steam heaters, 
however, are not to be considered as economizers of heat. 

MECHANICAL STOE^ERS. 

• The principles governing the operation of mechanical or 

'automatic stokers are in the main correct, viz., that the 

ijhsupply of coal and air is continuous, and that provision is 



Mechanical Stokers 



199 



made for the regulation of the supply of fuel according to 
the demand upon the boiler for steam; also that the in- 
termittent opening and closing of the furnace doors, as in 
hand firing, thereby admitting a large volume of cold air 
directly into the furnace on top of the fire, is avoided. 

Mechanical stokers have within the last twelve years 
been largely adopted in the United States, especially in sec- 
tions where bituminous coal is the principal fuel. The 
disadvantages attending their use are : 




Fig. 77 
cahall vertica boiler with chain grate stoker attached 

First, that the cost of properly installing them is so 
great that their use is practically prohibited to the small 
manufacturer. 

Second, that in case of a sudden demand upon the boilers 
for more steam the automatic stoker cannot respond as 
promptly as in hand firing, although this objection could 
no doubt be met by skillful handling. 



200 Steam Engineering 

Third, the extra cost for power to operate them, al- 
though this is probably offset by the diminished expense 
for labor required, as compared to hand firing. 

There are many different types of mechanical stokers, 
and automatic furnaces, but they may for convenience be 
grouped into four general classes. In class one, the grate 
consists of an endless chain of short bars that travel in a 
horizontal direction over sprocket wheels, operated either 
by a small auxiliary engine or by power derived from an 
overhead line of shafting in front of the boilers. 

In class two may be included stokers having grate bars 
somewhat after the ordinary type as to length and size, but 
having a continuous motion up and down or forward and 
back. This motion, though slight, serves to keep the fuel 
stirred and loosened, thus preventing the firing from be- 
coming sluggish. The grate bars in this class of stokers 
are either horizontal, or inclined at a slight angle, and their 
constant motion tends to gradually advance the coal from 
the front to the back end of the furnace. 

Class three includes stokers having the grate bars steeply 
inclined. Slow motion is imparted to the grates, the coal 
being fed onto the upper end, and forced forward as fast 
as required. 

Class four includes an entirely different type of stoker, 
in that the fresh coal is supplied underneath the grates, 
and is pushed up through an opening left for the purpose 
midway of the furnace. The gases, on being distilled, im- 
mediately come in contact with the hot bed of coke on top, 
and the result is good combustion. In this type of stoker, 
steam is the active agent used for forcing the coal up into 
the furnace, either by means of a long, slowly revolving 
screw, as in the American stoker, or a steam ram, as with 




Mechanical Stokers 



201 



the Jones under-feed stoker. A forced draft is employed, 
and the air is blown into the furnace through tuyeres. 




Fig. 78 
mansfield chain grate stoker 
Showing How it Can Be Withdrawn from under Boiler 
i 

When these stokers are intelligently handled they give good 
results, especially with cheap bituminous coal. The clinker 
formed on the grate bars or dead plates is easily removed. 



202 



Steam Engineering 



The coal is supplied to mechanical stokers, either by be- 
ing shoveled by hand into hoppers in front of, and above 
the grates, or, as is the case in most of the large plants 
using them, it is elevated by machinery and deposited in 
chutes, through which it is fed to each boiler by gravity. 
Stokers of the chain grate variety are usually constructed 
so that they may be withdrawn from underneath the boiler 
in case repairs are necessary. The coal, either nut or 
screenings, is fed into a hopper in front of and above the 




level of the grate, and is slowly carried along towards the 
rear end. The ash drops from the grate as it passes over 
the sprocket wheel at the rear. 

Fig. 76 shows a battery of Babcock & Wilcox water-tube 
boilers fitted with chain grate stokers. The buckets for 
elevating the coal to bins overhead, from whence it is fed by 
gravity to the stokers, are not shown. These buckets or 
carriers may also be utilized for conveying the ashes from 
the boiler-room. 



Mechanical Stolcers 203 

Fig. 77 is a sectional view of a vertical Cahall boiler with 
a Mansfield chain grate stoker^ and Fig. 78 shows the same 
stoker withdrawn from the boiler. 

The Coxe mechanical stoker operates upon the same gen- 
eral principles as do those previously described, being of 




Fig. 80 
vicars mechanical stoker 



the chain grate type, but it has in addition a series of air 
chambers just underneath the upper traveling grate. These 
air chambers are made of sheet iron, and are open at the top 
and provided with dampers for regulating the air pressure 
for different sections of the grate. The air blast is sup- 



204 Steam Engineering 

plied by a fan. Another feature of this stoker is a water 
chamber for the bottom section of tlie grate to travel 
through on its return. 

The P.layford stoker has wrought iron T bars extending 
across the furnace and attached to the traveling chains. 
These T bars carry the small cast iron sections composing 
the grate. A screw coiiveyor is also placed' in the ash pit 
for the purpose of carrying the ashes from the rear to the 
front of the pit. Fig. 79 is a sectional view of the Playford 
stoker attached to a water-tube boiler. 

In class two may be included stokers having the grates in- 
clined more or less. In some varieties the grates incline 
from front to rear^ while in others they are made to incline 
from the side walls toward the center line of the furnace. 

In the Vicars mechanical stoker the grate bars are some- 
what of the shape of the ordinary grate, and lie in two tiers 
in a horizontal position. The lower or back tier next the 
bridge wall is stationary^ and is placed there for the pur- 
pose of catching what coal is carried over the ends of the 
upper or moving grate bars. These have a slow reciprocat- 
ing motion which gradually moves the hot coke back 
towards the bridge wall. The coal is fed from a hopper 
into two compartments^ from which it is pushed by recipro- 
cating plungers onto a coking plate and from thence it 
passes to the grate bars. The motion of these bars has 
several intermediate variations, from a state of rest to a 
movement of 3I/2 inches. They have a simultaneous move- 
ment forward by which the fuel is advanced, but on the 
return movement the bars act at separate intervals. In this 
manner the fuel remains undisturbed by the return motion 
of the grates. Fig. 80 illustrates this stoker. 



Mechanical Stokers 



205 




Fig. 81 

FURNACE VIEW, WILKINSON STOKER 

In the WilJcinson stoker, Fig. 81, the grate bars are hol- 
low and are set at an angle of 20°, the inclination being 
from front to back. Each bar is stepped along its fire 



206 



Steam Engineering 



surface;, and on the rise is perforated with a long, narrow 
slot. A steam pipe extends along the front of the furnace. 




Fig. 82 
wilkinson stoker 



and from this pipe small branch pipes lead into the ends 
of the grate bars, which latter are in fact a series of hollow 
trunks with their front ends open. When in operation a 



Mechanical StoJcers 



207 



steam blast is admitted to each of the several trunk grate 
bars through the small branch pipes^ and this blast induces 
an air current of more or less pressure^ which finds an 
outlet through the narrow slots in the stepped fire surface 
of the grates, and directly into and through the burning 
mass of fuel. A slow reciprocating motion is imparted to 
the grates by means of cranks and links operated from an 




Fig. 83 
the mukphy automatic furnace 

overhead shaft; see Fig. 82. These cranks are set alternate- 
ly at 90° with each other, thus giving a forward movement 
to one-half of the grate bars, while at the same time the 
other half is moving backward. In this manner the fuel 
is kept slowly moving down the inclined grates. 

The Murphy Automatic Furnace, a sectional view of 
which is shown in Fig. 83, has the grates inclined inwards 
from the side walls, while a fire brick arch is sprung from 



208 Steam Engineering 

side to side to cover the entire length of the grate. The 
coal is shoveled or fed by carrier into the coal magazines, 
one on each side^ as shown in the cut. If the furnace is 
placed directly under the boiler it necessitates putting 
these coal magazines within the side walls, but as the 
Murphy furnace is usually constructed at the present day 
as an outside furnace^ the coal magazines are independent 
of the boiler walls. 

The bottom of each magazine is used as a coking plate, 
against which the upper ends of the inclined grates rest. 
On the central part of this plate is an inverted open box. 
This is termed the ^^stoker box/^ and it is moved back and 
forth across the face of the coking plate by means of a 
shaft with pinions that mesh into racks under each end of 
the box. By means of this motion of the stoker boxes the 
coal is pushed forward to the edge of the coking plate and 
from thence it slowly passes down over the inclined grates 
toward the center of the furnace. At this point the slowly 
rotating clinker breaker grinds the clinker and other refuse 
and deposits them in the ash pit. 

Above the coking plates are the ^^arch plates/^ upon 
which the bases of the fire brick arch rest. These plates 
are ribbed, the ribs being an inch apart, and, the arch rest- 
ing upon these ribs, there is thus provided a series of air 
ducts by means of which the air, already heated by having 
been admitted in front and passed through the flues over 
the arch, is conducted into the furnace above the grates 
and comes directly in contact with the gases rising from 
'the coking fuel. Air is also admitted under the coking 
plate and, passing up through the grates, serves to keep 
them cool and also furnishes the needed supply to the 
burning coke as it slowly moves down toward the center. . 



Mechanical Stokers 209 



The fuel is aided in its downward movement by the con- 
stant motion of the grates^ one grate of each pair being 
moved up and down by a rocker at the lower end. 

Motion is imparted to the various moving parts of this 
furnace by means of a reciprocating bar extending across 
the outside of the entire fronts and to which all the work- 
ing parts are attached by links and levers. This bar is 
operated by a small engine at one side of the settings the 
power required being about one horsepower per furnace. 




Fig. 84 
sectional perspective of the roney mechanical stoker 

The Roney stoker consists of a set of rocking stepped 
grate bars^ inclined from the front toward the bridge wall. 
The angle of inclination is 37^. A dumping grate oper- 
ated by hand is at the bottom of the incline for the purpose 
of receiving and discharging the clinker and ash. This 
dumping grate is divided into sections for convenience in 
handling. 

The coal is fed onto the inclined grates from a hopper in 
front. The grate bars rock through an arc of 30^, assum- 



210 



Steam Engineering 



ing alternately the stepped^ and the inclined positions. Fig. 
84 is a sectional perspective view of this stoker and illus- 
trates the working parts. 

The grate bars receive their motion through the medium 
of a rocker bar and connecting rod. A shaft extending 
across the front of tlie stoker under the coal hopper car- 
ries an eccentric that gives m^otion to the connecting rod 
and also to the pusher in the coal hopper. This pusher^ 
working back and forth, feeds the coal over the dead plates 
onto the grates^ and its range of motion is regulated by a 




Fig. 85 



feed wheel from no stroke, to full stroke, according to the 
demand for coal. The motion of the grate bars may also 
be regulated by a sheath nut working on a long thread on 
the connecting rod. Each grate bar consists of two parts, 
viz., a cast iron web fitted with trunnions on each end that 
rest in seats in the side bearer, and a fuel plate Ixaving the 
under side ribbed to allow a free circulation of air. 

The fuel plate is bolted to the web and carries the fuel. 
The grates lie in a horizontal position across the furnace 
in the form of steps, and ample provision is made for the 



Mechanical Stohers 



211 



admission of air through the slotted webs. A fire brick 
arch is also sprung across the furnace^ covering the upper 
■ portion of the grate. 




Fig. 86 
new roney stoker as it appears in furnace 

This arch^ being heated to a high temperature, serves in 
a measure to partly coke the coal as it passes under it. Air 
is also admitted on top of the coal at the front. This air 



212 Steam Engineering 

is heated by its passage throiigli a perforated tile over the 
dead plate and adjoining tiie fire brick arch. Fig. 85 
shows the location of the arch and tile. 

The Westinghouse Machine Company has recently de- 
signed an improved model of the Eoney mechanical stoker. 
Some of the most important features in connection with 
its design is, that the number of complete grate bars has 
been reduced one-half over that used with the old type of 
stoker. The tops, webs, guards and dumping grates are 
interchangeable. The grate bars automatically center 
themselves in the side bearings by their own weight; they 
may also be re-distributed so as to equalize wear over all 
parts of the furnace. The guard and dumping grates are 
interchangeable without disturbing the side or center bear- 
ings. Fig. 86 shows the stoker as it appears in a furnace 
setting. 

For the upper four grates a non-sifting type of top is 
used, provided with abutting, horizontal ledges to prevent 
the fine fuel from sifting through the bars, and at the 
same time permit a free entrance of the air. For each 
square foot of grate exposed to the fire, 7.4 square feet of 
surface is cooled by the air, giving 7.4 times the cooling 
effect of the flat-top grate bar. ' 

As will be seen from Fig. 87, the grate proper consists 
of a number of thin plates set on edge in V-grooves. These 
hook over a trussed web, and are held in place by a key- 
rod slipped in from the end. They are, therefore, easily re- 
moved. One of the principal advantages of the sectional 
grate-bar tops is, that it reduces the amount of scrap when 
they have been sufficiently worn to be discarded. In this 
stoker no bolts are used, and any part can be removed 
without disturbing the other. 



Mechanical Stohers 



213 




Fig. 87 

roney stoker 

Showing Construction of Grate 



214 Steam Engineering 

The new type of guard prevents the fire froqii sliding into 
the ash-pit when the dumping grate is operated. As the 
lower end of the guard is now raised, instead of cutting 
through the fire, as formerly, it not only makes it possible 
to dislodge from the fire all clinker formed at the bottom, 
but also provides an unobstructed descent for the ash and 
clinker separately. When dropped to its normal position, 
it permits the lower edge of the fire to settle quietly 
without a tendency to slide. 

The new dumping grate is hinged about one-third for- 
ward, dumping both front and rear. Being nearly bal- 
anced, it is very easily operated. The upward motion of 
the dumping grate breaks up any clinker bridge tending 
to form between the grates and bridge-wall. 

In mechanical stokers of the under-feed type the air is 
supplied by forced draft. 

The American stoker consists of a horizontal conveyor 
pipe into which the coal is fed from a hopper. The diam- 
eter of this pipe depends upon the quantity of coal to be 
burned, and varies from 4I/2 inches for the smaller sizes 
up to 9 and 10 inches for the larger sized stokers. The 
length of the conve3^or pipe for the standard 10-inch stoker 
is 72 inches. Attached to the outer end of this conveyor 
pipe, and forming a part of it, is an iron box containing a 
reciprocating steam motor, which, through the medium of 
a rocker arm, and pawl and ratchet wheel, drives a screw 
conveyor shaft that slowly revolves within the pipe, thus 
forcing the coal forward and up through another box or 
trough, which latter is wholly within the furnace. Extend- 
ing around the top edges of this box, and on a level with 
the grate bars, there is a series of tuveres through which 
the air is forced. 



Mechanical Stokers 



215 




Fig. 88 
typical setting of american stoker under a return tubular 

BOILER 

These tuyeres, being at a high temperature, serve to heat 
the air in its passage through them, thus greatly aiding 
combustion. Fig. 88 is a longitudinal sectional view of 
this stoker. 



216 Steam Engineering 

The speed of the screw conveyor is regulated by the hand 
throttle of the motor^ according to the demand for coal. 
With the 9-inch standard stoker from 350 to 1;,200 pounds 
of coal per hour may be burned. Fig; 89 is a view of the 
American stoker before being placed in position in the 
furnace. 

The air jets^ passing out from the tuyeres in a horizontal 
direction, and from opposite sides, cut through the rounded 
bed of coal and the gases are thus ignited and consumed 
immediately after being distilled from the coal, while the 
pressure of the coal rising from underneath forces the al- 
ready coked fuel over the edges of the trough or box onto 
the grates which occupy the space between the side walls 
and the coal trough. The air is first delivered from the 
fan into the air box that surrounds the coal trough on 
three sides and from thence it passes to the tuyeres. If 
this stoker is properly handled very good results may be 
obtained by its use, but, like all other devices for burning 
coal under boilers, it is bad policy to endeavor to force it 
beyond its capacity. 

In the Jones under-feed stoker the coal is pushed for- 
ward and up into the furnace through a cast iron retort or 
trough. The impelling force is a steam ram connected to 
the outer end of the retort, and the speed of the ram is 
regulated automatically by the steam pressure, or by' hand 
as desired. The coal is supplied to the ram through a cast 
iron hopper having a capacity of 125 to 140 pounds. 

Force draft is also employed in this stoker, the air being 
conducted from the fan or bloAver through galvanized iron 
pipes into the closed ash pit, which .really forms an air box, 
as the space on either side of the retort that is usually 
occupied by grate bars is in this case covered by solid cast 



Meclianical Stokers 



217 









' 


S^ 


^ 




i 




1 


wm 




u i 


j 




1 


H 




[iS;: H 






1 


■^^9-1':]- 




- v^ JH 






BK 


^^l^^ff 




1 1 i^H 


*'jR 




1 


0-, 




. J^^^^^^^y 






■ 




|< 








■ 




r 


u ^E^S 






H 




r 


"^ iJ^^S 


8 




1 


^»:ft|g||if:;.. 




tiii ■ 




r^tW 


■ 




.J 



Fig. 89 
standard 8 and 9 inch american stokers 

A — Coal hopper; B — Conveyor pipe; C — Tuyeres for intro- 
ducing air to the fuel ; D — Opening to wind-box for air connec- 
tions ; E — Wind- box for supplying air to tuyeres ; K — Automatic 
steam motor for driving conveyor ; R — Air pipe to wind-box ; 
S — Gas ducts for returning volatile products from entering coal 
to furnace. 



218 Steam Engineerinq 

iron dead plates^ upon which the coked fuel lies until it is 
consumed. These plates^, being hot^ serve to heat the air 
coming in contact with them in its passage to the cast iron 
tuyeres through which it passes to the bed of burning fuel 
in the retort. Air entirely surrounds the retort on the sides 
and back end, and is at a constant pressure in the ash 
pit, but can only pass into the furnace through the tuyeres^ 
the jets of air cutting through the rounded heap of in- 
candescent fuel from opposite sides^, and in a direction in- 
clined upwards. 




Fig. 90 

Coal is supplied to the hopper either by hand, or by 
mechanical means where the plant is fitted with coal- 
handling machinery. The opening through which it passes 
from the hopper to a position in front of the ram is 8x10 
inches in size. Each charge of the steam ram carries for- 
ward 15 to 20 pounds of coal. Connected to the ram, and 
moving in conjunction with it is a long rod extending 
through the retort near the bottom. Upon this rod are 
carried shoes that act as auxiliary plungers and facilitate 
the movement of the coal. 

Fig. 90 is a sectional view of the Jones stoker, showing 
the machine full of coal, with the ram ready to make a 



Mechanical Stokers 219 

charge. Pig. 91 shows the stoker complete before being 
placed in the furnace. 

It is claimed by the builders of under-feed stokers^ and 
the claim appears to have good foundation, that by pushing 
the green coal up, so as to meet the upper crust of ,i^lowing 
fuel the gases on being distilled immediately come in con- 
tact with, and are consumed by the burning mass, and the 
formation of smoke is thus prevented. Both the Jones 
under-feed, and the American stokers have proved to be 
very successful in the burning of the cheaper bituminous 
coals of the West. One feature tending to commend them 




Fig. Ul 



is the fact that practically all of the coal is utilized, there 
being no waste caused by the slack coal or fine screenings 
dropped through the grate bars into the ash pit uncon- 
•sumed. 

A good substitute for the mechanical stoker is an outside 
furnace, by which is meant a boiler installation having the 
furnace in front of, instead of underneath the boiler. One 
of the principal hindrances to good combustion in the ordi- 
nary type of boiler furnace is the fact that the temperature 
I of the boiler shell or water tubes with which the gaseous 
I products of combustion come in contact can never be higher 
lihan the temperature of the water contained within the 



220 Steam JSngineering 

boiler. This temperature ranges from 297^ for steam at 
50 pounds gauge pressure^ up to 407° for 255 pounds 
pressure, while the temperature of the furnace, according 
to Dr. Thurston and other high authorities, ranges from 
2,010° to 2,550°. 

It is evident that perfect combustion does not take place 
until these high temperatures are reached. Each time the 
furnace is charged with fresh coal, especially if the boiler 
be hand-fired, a large volume of volatile gases is liberated, 
but not consumed. If these gases are allowed to immediate- 
ly come in contact with a comparatively cool surface, as 
for instance the heating surface of the boiler, the result is 
a cooling of the gases, incomplete combustion and the 
formation of smoke and soot. If, on the other hand, the 
furnace is so constructed that these gaseous products first 
impinge against hot surfaces, such as fire brick arches or 
bafflers that have a temperature corresponding to that of 
the furnace, good combustion is assured. This condition 
is in a large degree attained by the use of outside furnaces, 
thair permit the construction of a fire brick arch to cover 
the entire grate surface. 

The Burke furnace, patented by James V. Burke of 
Chicago, is a notable example of this type of furnace. It is 
applicable to any type of stationary boiler. Fig. 92 shows 
this furnace as applied to tubular boilers. It consists of a 
fire brick arch extending from 6 to 8 feet outwards from 
the boiler front, and of a width to correspond to the diame- 
ter of the boiler. The arch rests securely upon brick work 
inclosed in a well ventilated iron casing. There is prac- 
tically no heat radiated from this furnace, all the heat gen- 
erated by it passing to the boiler. The central portion of p 
the grate bars consists of shaking grates, while the side bars ' 
are stationary ^nd inclined. 



bpi 



Mechanical StoTcers 



221 



Fig. 93 is a sectional view and will serve to illustrate 
the construction of this furnace. The coal is fed through 
pockets on top on each side of the arch, the larger furnaces 
having two pockets on each side and the smaller sizes one. 




Front View* 

Fig. 92 

burke furnace 



The doors in front are only opened for the purpose of 
cleaning fires, or when first starting fires. The air is sup- 
plied by way of the ash pit, passing up through the grate 
oars. A portion of the air supply is also drawn through 
ihe ventilators and passes to the upper part of the furnace. 



222 



Steam Engineering 



The arch extends under the front end of the boiler 6 or 8 
inches, and there is a bridge wall about 4 feet back from 
the fronts against which the gases from the furnace im- 
pinge. 

There are 42 square feet of grate surface in the larger 
sizes, and 22 square feet in the smaller size. Good com- 
bustion is attained in this furnace, owing to the fact that 
the gases as they are distilled from the coal come imme- 




Fig. 93 
burke furnace 

diately in contact with the highly heated surface of the 
arch directly over the fire. 

Stoker selection and stoker installation furnish prob- 
lems requiring a high order of mechanical skill, knowledge 
of many details and freedom from bias and prejudice. 
Each installation must be studied individually, and the size 
and type of stoker and subsidiary details of grate, draft, 
furnace, etc., determined only after an exhaustive consider- 



Mechanical Stokers 223 

ation of all points. Thus and only thus may the highest 
economy be realized^ for it is economy primarily that must 
be sought and secured in this day of keen competition^ with 
a smokeless stack as a secondary consideration. 

It is a facty well recognized by all students of boiler fur- 
nace combustion, that smoke suppression does not neces- 
sarily mean fuel economy, while it is universally recog- 
nized that when combustion is complete with fuel economy 
at its highest, there can be no smoke. 

The very considerable initial cost of installing mechan- 
ical stokers may no longer be regarded as a species of 
speculation, but as a sound investment that returns a 
truly marvelous annual dividend. It is not overstating 
the facts, as well recognized by progressive and studious 
engineers that there is no other single piece of power plant 
equipment that will pay a richer dividend on its cost than 
a properly constructed, properly selected, properly installed 
mechanical stoker. 

It is totally impossible to duplicate the condition of a 
stoker-fired furnace with one in which the coal is fed by 
hand through the firedoor. 

MECHANICAL DRAFT. 

Application of mechanical draft assumes three general 
forms : First, induced draft by the installation of fans 
to serve as a chimney. Second, forced draft by applying 
fans to force air beneath boiler grates. Third, the com- 
bination of induced and forced draft, obtained by fans ap- 
plied to serve both purposes, or by separate fans for each. 
Many large plants are now installed where this combina- 
tion is employed, the combined forced and induced draft 
system being ^brought about on account of equipping the 



224 Steam Engineering 

boilers with any make of stokers^ outside of the chain type 
or those having the open ash pit. Air^ under a pressure 
of one and one-fourth to two ounces^ is delivered to the 
stokers by a forced draft fan^ the separate induced draft 
f an^ or fans being connected in the ordinary manner^ with 
the boiler breeching^ with or without economizer in con- 
nection^ and discharge the gases through a steel stack into 
the atmosphere. Under this class may also be included 
the method of burning powdered fuel in suspension. The 
practicability of the system has been thoroughly demon- 
strated by tests extending over a number of months, but, 
"while the system has shown a marked degree of efficiency, 
it has seldom been made use of in practice. The selection | 
of the proper type to render the highest economy, primarily 
depends upon the fuel to be consumed^ and the various 
conditions of the steam plant to be outfitted. It is readily 
seen that no single one of these three applications of me- 
chanical draft will give the best results in all cases, but that 
every boiler plant must be carefully treated individually. 
Mechanical Induced Draft is by no means a new idea, 
yet it is only within a few years that the same draft has 
been much used or installed on a large scale. Previously 
it had been used, with a few exceptions, for the purpose of 
improving poor draft by helping out an insufficient or an 
overloaded chimney. The largest and most successful ap- 
plications of mechanically induced draft have been made 
in connection with feed water heaters designed to utilize 
the waste heat of the flue gases, and known as fuel econo- 
mizers. This form of feed- water heaters has been manu- 
factured in England for over fifty years. They have, how- 
ever, been imported for many years, as their value as a fuel 
saving device is well established. Their successful opera- 



Mechanical Draft 225 

tion is so dependent upon good draft that no well-informed 
engineer would think of installing an economizer without 
making provision for much better draft than the boilers 
would require without it. On account of the reducing ef- 
fect on the drafts caused by lowering the temperature of 
the gases and retarding their flow by the mechanical inter- 
ference of the pipes^ it cannot be considered good engineer- 
ing to attach an economizer to a chimney less than 200 feet 
in height. The best working economizers in connection 
with chimneys are those where the chimney is considerably 
over 200 feet high. 

Forced Draft has been used for years^, the original instal- 
lations being principally for burning refuse materials^ and 
for assisting boiler draft of natural low efficiency. The 
advancement to popular favor has been of healthy but grad- 
ual growth. In the early stage it was commonly supposed 
that what would now be called in mechanical draft a high 
air pressure -was absolutely essential to best results. As this 
type of mechanical draft has developed^ it is noticeable that 
in succeeding representative plants^ the velocity of air has 
gradually decreased^ until now it is generally recognized 
that forced draft outfits show the best results where a suf- 
ficient air volume is used at the lowest pressure which se- 
cures complete combustion. Practice has established the 
fact that this is more economical than using the same 
quantity of air at double the velocity^ because of less liabil- 
ity to blow holes^ less unconsumed particles carried up to 
the stack^ and less horse power consumed by the fan. 

As is at once understood^ the term ^"^forced draff' used 
in connection with a steam plant refers to the forcing of the 
air under the grates. The favorite point of introduction 
into most boilers is through the bridge wall at the rear end 



226 Steam Engineering 

of the grates. Where this arrangement is not feasible, 
however, quite as efficient results are obtained through side 
walls, or further in front, using properly arranged dampers 
with convenient accessories for manipulation. 

Occasionally objections to forced draft are urged, on the 
ground that with its use there is an outward leakage of 
gases, and blow holes through boiler fires at diflEerent grate 
intervals. Such results only occur with poor applications 
and installation details, or with improper firing. The meth- 
od of introduction of the air to the grates, and the appli- 
ances therefor, figure conspicuously in the securing of max- 
imum economy and efficiency. 

Where the air supplied to the fan is taken from an air 
chamber built around, or through the smoke breeching — 
and herein is embodied an important saving — the tempera- 
ture of the air supply, and consequently the temperature of 
the furnace is raised while the temperature of the gases in 
the breeching is reduced. With natural draft this would 
tend to reduce the velocity in the stack. It is highly de- 
sirable that the fan be driven by an individual engine, with 
the valve controlling the steam supply thereto equipped 
with the special arrangement for governing the speed of 
the engine, according to the draft requirements. In brief, 
the principle of this consists of automatically supplying 
more steam to the engine when the boiler pressure lowers, 
and less steam when the steam pressure increases. This 
has been brought to so fine a point that practically a con- 
stant pressure is maintained on the boilers with proper 
firing. 

Direct advantages exist in favor of forced draft where 
certain conditions exist. The chimney of a given steam 
plant ^nay be capable of handling the boilers, excepting un- 



Mechanical Draft 



227j 




Fig. 94 
buffalo mechanical draft apparatus 
Horizontal Tandem Fans — Casing and Economizer Partly Re- 
moved to Show Damper 

der adverse conditions of weather, when a blower properly 
applied needs only to be started and run during such pe- 
riods. While the capacity of a chimney, either with forced 
or natural draft, is limited, the natural efficiency may be 



228 



Steam Engineering 



materially increased^ so that if more boilers have been 
added than the chimney will properly handle without some 
assistance, this may be afforded by the proper application 
of a blower to force air into the ash-pit. 

Fig. 94 shows part of a large steam plant equipped with 
an induced draft apparatus supplied by the Buffalo Forge 




Fig. 95 
three-quaeter housing steel plate fan with double hori- 
zontal engine 



Co.^ Buffalo^, N. Y. A portion of the casing is removed in 
order to show the location of the economizer. 

Fig. 95 shows another style of fan having double hori- 
zontal engines^ one on each side of the crank shaft, which is 
extended into the fan, and forms a direct-attached machine 
by reason oi the fan wheel being placed on the opposite end 
of the shaft. But one of the engines is intended for use at 



Mechanical Draft 229 

a time^ the other rod being disconnected and held in reserve 
in case of an accident^ although the design is such that 
both may be operated simultaneously^ if desired. In the 
construction of this engine^ the desirable point of being able 
to quickly change from the right to the left-hand engine^ 
or the reverse^ at the same time keeping a perfect balance^ 
has been embodied. This feature is accomplished in the 
following manner : The disc is made sufficiently heavy on 
the side on which the pin is placed to counterbalance the 
crank and connections when the left-hand engine connected 
to the crank is in use. Then when the left-hand engine is 
disconnected and the right-hand engine is connected up, 
the pocket provided in the disc on the opposite side from 
the pin is filled with shot, and the balance re-established for 
the right-hand engine, when the left-hand engine is held in 
reserve. The pocket in which the shot is placed is stopped 
with a threaded plug inserted with a screw-driver and 
makes a neat finish. It may be filled or emptied in a few 
seconds^ time. The crank shaft is of forged steel, of ample 
proportions, which is a distinguishing feature of Buffalo 
Steam Fans. Sufficient space is left between the crank and 
the disc for the eccentric, and a bearing of ample wearing 
proportions. The valves employed are of the piston type, 
carefully fitted up with cages, and snap ring packing. They 
are attached to the valve stem by a simple, efficient method, 
•which permits of the removal of the valve with the great- 
est ease. Other general construction details are similar to 
those found in the Buffalo center-crank engines. 

The illustration shows a large fan in three-quarter steel 
plate housing, the lower portion of the scroll being brick- 
work, and is used for blowing a battery of stationary boiler 
fires. 



230 Steam Engineering 

Combined induced and forced draft applied to a bat- 
tery of boilers is somewhat unusual^ but the BuflEalo Special 
Steel Plate Fans have been thus employed with excellent 
results. The combined system being employed because of 
equipping the boilers with stokers, requiring a closed ash 
pit. Certain special boilers are designed particularly for 
induced and forced draft, and to these have applications 
been made, with the result of obtaining more than a regular 
amount of steaming capacity within a given space. Ordi- 
nary boilers have also been thus outfitted with considerably 
increased capacity. 

The combination may be installed in two ways, as fol- 
lows : First, with two separate fans, one an induction, and 
the other an eduction fan. Second, with a single fan of 
special construction, having a web or divided wheel and 
two inlets, one to receive the intake of gases from the boiler 
stack, and the other to receive fresh air, the amount handled 
being regulated by an oscillating damper. The former 
arrangement is necessitated for the special boiler construc- 
tion alluded to, and is also applicable to large steam plants 
with ordinary, water-tube, or tubular boilers with or without 
equipments of economizers, and burning fuel of low grades. 
The fan for forcing air under the grates is usually some- 
what the smaller of the two. 

The more simple plants of combined induced and forced 
draft employ the one fan arrangement, which is built with 
two inlets and takes in unheated air on one side. Connec- 
tion, by m,eans of a suitable pipe, is made with the chimney 
flue or smoke breeching of the boiler to the other side of 
the fan, thereby taking in the larger part of the flue gases. 
These are mixed with the fresh air taken in from the other 
side of the fan as it leaves the outlet and is being 



Mechanical Draft 231 

delivered to the ash-pit of the furnaces. From thence the 
air is forced through the grates to the fuel bed. Dampers 
are used on each side to regulate the proportion of air and 
flue gases admitted to the fan. Eecently published tests of 
such apparatus using Buffalo Special Steel Plate Fans, 
show an average temperature of the air discharged under 
the grates of 235 degrees, and naturally a great gain in 
efficiency over the same boilers without the device. 

The importance of good draft, either natural or arti- 
ficial, for supplying sufficient oxygen for the economical 
combustion of fuel has long been recognized by intelligent 
engineers. The gain, both in efficiency and capacity, ob- 
tained by the rapid and energetic combustion of fuel, and 
the resulting high furnace temperatures is well established. 
Its importance has been generally conceded only within a 
few years. To obtain this high furnace temperature re- 
quires draft sufficiently strong to deliver an abundant sup- 
ply of oxygen to the furnace. 

CHIMNEYS. 

Chimneys are required for two purposes — first, to carry 
off obnoxious gases; second, to produce a draft, and so fa- 
cilitate combustion. The first requires size, the second 
height. 

The weight of gas to be carried off by a chimney in a 
given time depends upon three things — size of chimney, 
velocity of flow, and density of gas. But as the density 
decreases directly as the absolute temperature, while the 
I velocity increases, with a given height, nearly as the square, 
root of the temperature, it follows that there is a tempera- 
ture at which the weight of gas delivered is a maximum. 
This is about 550° above the surrounding air. Tempera- 



232 Steam Engineering 

ture, however^ makes so little difference^ that at 550^ 
above;, the qnantity is only four per cent greater than at 
300°. Therefore^ height and area are the only elements 
necessary to consider in an ordinary chimney. 

The intensity of draft is^ however^ independent of the 
size^ and depends upon the difference in weight of the out- 
side and inside columns of air^ which varies nearly as the 
product of the height into the difference of temperature. 
^ This is usually stated in an equivalent column of water, 
and may vary from to possibly 2 inches. 

After a height has been reached to product draft of suf- 
ficient intensity to burn fine, hard coal, provided, the area 
of the chimney is large enough, there seems no good me- 
chanical reason for adding further to the height, whatever 
the size of the chimney required. Where cost is no consid- 
eration, there is no objection to building as high as one 
pleases; but for the purely utilitarian purposes of steam 
making, equally good results might be attained with a 
shorter chimney at much less cost. 

The intensity of draft required varies with the kind and 
condition of the fuel, and the thickness of the fires. Wood 
requires the least, and anthracite screenings the most. The 
strong draft required for burning the smaller sizes of an- 
thracite coal necessitates a very tall chimney, unless forced 
blast is used. 

Generally a much less height than 100 feet cannot be 
recommended for a boiler, as the lower grades of fuel can- 
not be burned as they should be with a shorter chimney. 

A round chimney is better than square, and a straight 
flue better than a tapering, though it may be either larger 
or smaller at the top without detriment. 



Chimneys 233 

The effective area of a chimney for a given power varies 
inversely as the square root of the height. The actual area, 
in practice, should be greater, because of retardation of ve- 
locity due to friction against the walls. On the basis that 
this is equal to a layer of air two inches thick over the 
whole interior surface, and that a commercial horsepower 
requires the consumption on an average of 5 pounds of coal 
per hour, we have the following formulas : 

0.3 H ' 

E= — -_=A— 0.6 VA 1 

H=3.33 E ^/~h^, 2 

S=12 V^+4. , 3 

D=13.54 VE+4:. .;•••, ^ 

/0.3H2\ 
li=\ ^ 



(^) 



in w^hich H=horsepower ; h—.\ieighi of chimney in feet; 
E=effective area, and A=:actual area in square feet; S= 
side of square chimney, and D=dia. of round chimney in 
inches. Table 15 is calculated by means of these formulas. 
To find the draft of a given chimney in inches of water : 
Divide 7.6 by the absolute temperature of the external air 
(ra=^t-{-Jf60) ; divide 7.9 by the absolute temperature of 
the gases in the chimney (tc=^'+4^^)V subtract the latter 
from the former, and multiply the remainder by the height 
of the chimney in feet. This rule, expressed in a formula, 
would be : 



d=h 



(7.6 7.9 \ 



234 Steam Engineering 

To find the height of a chimney, to give a specific draft 
power^ expressed in inches of water: Proceed as above, 
through the first two steps, then divide the given draft 
power by the remainder, the result is the height in feet. 
Or^ by formula : 



h-- 



d 



7.6 7. 



7,9 \ 
re-j 



To find the maximum efficient draft for any given 
chimney^ the heated column being 600° F.^ and the ex- 
ternal air 62° : Multiply the height above grate in feet by 
.007, and the product is the draft power in inches of toater. 

The diagram;, Fig. 96^ shows the drafts, in inches^ of wa- 
ter for a chimney 100 feet high, under different tempera- 
tures, from 50° to 800° above external atmosphere, which 
is assumed at 60°. The vertical scale is full size, and each 
division is 1/20 of an inch. It also shows the relative 
quantity, in pounds of air, which would be delivered, in the 
same time, by a chimney under the same differences of 
temperature. It will be seen that practically nothing can 
be gained by carrying the temperature of the. chimney 
more than 350° above the external air at 60°. 

To determine the quantity of air, in pounds, a given 
chimney will deliver per hour, multiply the distance in 
inches, at given temperature, on the diagram. Fig. 96, by 
1,000 times the effective area in square feet, and by the 
square root of the height in feet. This gives a maximum. 
Friction in flues and furnace may reduce it greatly. 

The external diameter of a brick chimney at the base 
should be one-tenth the height, unless it be supported by 



Chimneys 



235 



some other structure. The "batter'' or taper of a chim- 
ney should be from ^q to l^ inch to the foot on each side. 




Fig. 96 



Thickness of brick work: one brick (8 or 9 inches) for 
25 feet from the top, increasing 1/4 brick (4 or 41/2 inches) 
for each 25 feet from the top downwards. 



236 



Steam Engineering 



If the inside diameter exceed 5 feet the top length 
should be 11/2 bricks, and if under 3 feet it may be ^2, 
brick for ten feet. 



Table 14 

theoretical draft pressure in inches of water in a 
chimney 100 feet high. 

(For other heights the draft varies directly as the height.) 



Temp, 
in 


TEMP. OF EXTERNAL AIR. (Barometer 30 Inches,) 


Chimney 


















1 




Fahr. 


0° 


10« 


20<' 


30° 


40«» 


50° 


60° 


70° 


80° 


90° 


100° 


200° 


.458 


.419 


.384 


,353 


.321 1 .292 


.263 


.234 


.209 


.182 


.157 


220 


.488 


.458 


.419 


.888 


.855 


.326 


.298 


.269 


.244 


.217 


.192 


240 


.520 


.488 


.451 


.421 


.388 


.359 


.330 


.301 


.276 


.250 


.225 


260 


.555 


.528 


.484 


.453 


.420 


.392 


.363 


.334 


.309 


.282 


.257 


280 


.584 


.549 


.515 


.482 


.451 


.422 


.394 


.365 


.840 


.813 


.288 


300 


.611 


.576 


.541 


.511 


.478 


.449 


.420 


.392 


.367 


.340 


.315 


320 


.637 


.603 


.568 


.538 


,.5C5 


.476 


.447 


.419 


.394 


.367 


.342 


340 


.662 


.638 


.593 


.563 


.530 


.501 


.472 


.443 


.419 


.392 


.367 


360 


.687 


.653 


.618 


.588 


.555 


.526 


.497 


.468 


.444 


.417 


.392 


380 


.710 


.676 


.641 


.611 


.578 


.549 


.520 


.492 


.467 


.440 


.415 


400 


.732 


.697 


.662 


.632 


.598 


.570 


.541 


.518 


.488 


.461 


.436 


420 


.753 


.718 


.684 


.658 


.620 


.591 


.568 


.584 


.509 


.482 


.457 


440 


.774 


.739 


.705 


.674 


.641 


.612 


.584 


.555 


.580 


.508 


.478 


460 


.793 


.758 


.724 


.694 


.660 


.682 


.608 


.574 


.549 


.522 


.497 


480 


.810 


.776 


.741 


.710 


.678 


.649 


.620 


.591 


.566 


.540 


.515 


500 


.829 


.791 


.760 


.730 


.697 


.669 


.639 


.610 


.586 


.559 


.534 



Tlie available draft will be the tabular values, less the 
amount consumed by friction in the stack. In stacks 
whose diameter is determined by the formulae, the net draft 
will be 80% of the tabular values. Hence to obtain from 
the table the height of stack necessary to produce a net 
draft of say 0.6 inches, the theoretical draft will be 0.6 X 
1.25=0.75 inches, which can be got with a stack 100 feet 
high with flue-gas temperature of 420° F., and air temper- 
ature of 0° F., or a stack 125 feet high when the air tem- 
perature is 60° F. 



Chimneys 



237 






CXWCOrOMMMM 

O'C^MCOOCiWOOOOi' 
C;«C0MH-*OiC0C0-lC0tO' 



-ICiCn^^COhONt'MMM. 
o oi CO ro CO i4^ O ^1 ^4^^ M • 
lO GO Ci ^1 O O-' 00 CO M CO • 



c;TCOM:ooociOT^*^oo^o^oM• 
co4^ocooooc:^j^4^c;iMOo« 

^ 0^ CO C< Ol ^J^ CI O GO OC CO to • 



Ci 4^ l-O O 00 ^1 OI h^i' CO to . 
M M M Ca: -1 ro :o -1 o: ^1 • 

05 ox 4^ GO O 00 CO l\5 01 t-^ • 



Diameter 
in Inches. 



tOrOMMMMM 
rf^MO^>4^roi-^<:D-JIOiCr<CO. 
^^►^^lOCDOOCO^ICOOOO' 
CDtOOiOOii4^-4>4i^05lOCOCO- 



^|i. CO CO CO hO to hO to M M M M M 

•coooscooorf^MOocirf^toooooc:^- 

OXC>4:^OOOOOCO-1COMMI0 4^00T- 
"MtOOOO-^tOCOOiiXiOOlOCOCDtOI-^' 



l4^ ij:^ CO CO CO to to to to i-i M M M 
-TCO O OT tC CO O, CO O -1 CJt CO M CO -1 • 
OMCO-ICOOCOOIO-ICOMOM*-- 
-vlMC;yxCOOCO>4i^CO--10MOO<0000- 



en rf^ *- CO CO CO to to to M M M M 
OOIOOOhii^O--l>^MOOC5i4^MCO' 
COOOtOCnO^lOiCSiCDCOOOOQO- 
MOOOlOlOCOCOtO^CO-lOMM* 



M 

OOG000-.10i0TUT^f^4i>.C0t0N:) to MMM 

P :-^ p M 00 CI 00 to Oi p 4^ P Ol p p CO p ;<l P p« 4^ W |s5 to M p 

^ ^ M o lo bo 00 lo o f-^ -1 ^ b bo o bx rfs- ^1 CI 4^ '*^ ^ ^1 o 4i. io 

t0C7C0OlOC0C0C0MC0a)C00DC000M4i.0i-I-<l00Q00000-<l-<l 





> 


, M 


r 


OX 




o 


o 


M 




or 


m 


l-K 


^ 


V' 


o 


o 


^ 


o 


m 


r? 


.^ 



rD -t o 



-.^K 



(T) c '-t 2 

rt S H) Q. 



2- (" H) d 

r ;^ {u {u 



s ^ 



O 

en 
W 
hj 
O 

O 

o 
1^ 

C/3 



Zron Chimneys, In many places iron stacks are pre- 
ferred to brick chimneys. Iron stacks require to be kept 



238 Steam Engineering 

well painted to prevent rust^ and generally, where not 
bolted down, they need to be braced by rods or wires to 
surrounding objects. With four such braces attached to an 
angle iron ring at 2/3 the height of stack, and spreading 
laterally at least an equal distance, each brace should have 
an area in square inches equal to .001 the exposed area of 
stack (diam. X height) in feet. 

Stability, or power to withstand the overturning force 
of the highest winds, requires a proportionate relation be- 
tween the weight, height, breadth of base, and exposed 
area of the chimney. This relation is expressed in the 
equation 

dh^ 
C =W, 

b 

in which d=the average breadth of the shaft; h=its height; 
b:=the breadth of base, — all in feet; W=weight of chim- 
ney in pounds, and C=a co-efficient of wind pressure per 
square foot of area. This varies with the cross-section of 
the chimney, and=56 for a square, 35 for an octagon, and 
28 for a round chimney. Thus a square chimney of aver- 
age breadth of 8 feet, 10 feet wide at base and 100 feet 
high, would require to weigh 5^X8X100X10=448,000 
pounds to withstand any gale likely to be experienced. 
Brickwork weighs from 100 to 130 pounds per cubic foot, 
hence such a chimney must average 13 inches thick to be 
safe. A round stack could weigh half as much, or have 
less base. 

Pure Air is a mixture of oxygen and nitrogen in follow- 
ing proportions: by volume 20.91 parts oxygen to 79.09 
parts nitrogen; by weight 23.15 parts oxygen to 76.85 parts 
nitrogen. Air in. nature always contains other constituents 



Chimneys 239 

such as dust^ carbon dioxide^ ammonia^ ozone and water 
vapor. 

Air being perfectly elastic^ the density of the atmos- 
phere decreases in geometrical ratio with the altitude. This 
fact has an important bearing on proportions of furnaces 
and stacks located in high altitudes^ as will later appear. 
The atmospheric pressure for different altitudes is given 
in Table 23. 

V7EIGHT AND VOLUME OF AIR. 

A cubic foot of air at 60° and under average atmos- 
pheric pressure^, at sea levels weighs 536 grains^ and 13.06 
cubic feet weigh one pound. Air expands or contracts an 
equal amount with each degree of variation in tempera- 
ture. Its weight and volume at any temperature under 
30 inches of barometer may be found within less than one- 
half of one per cent by the following formula^ in which 
W=weight in pounds of one cubic foot^ V=volume in 
cubic feet^ per pound^ and r^ absolute temperature^ or 
460° added to that by the thermometer, =t4-460. 

40 T 

Wz=— V=— 

T 40 

For any condition of pressure and temperature the fol- 
lowing formulas are very nearly exact: 

V r 

W=2.71— V= i5=2.71Vp— 460 

r 2.71/9 

in which p is pressure above absolute vacuum. The same 
formulae answer for any other gas by changing the co- 
efficient. 



240 Steam Engineering 

Table 16 

volume and weight of air at various tempera- 
tures, and atmospheric pressure. 



Temperature in 


Volume of one 


Weight of one 


Degrees Fahr. 


Pound Cu. Ft. 


Cu. Ft. in Lbs. 


50 


12.840 


.077884 


55 


12.964 


.077133 


60 


13.090 


.076400 


65 


13.216 


.075667 


70 


13.342 


.074950 


75 


13.467 


.074260 


80 


13.593 


.073565 


85 


13.718 


.072894 


90 


13.845 


.072230 


95 


13.970 


.071580 


100 


14.096 


.070942 


110 


14.346 


.069698 


120 


14.598 


.068500 


130 


14.849 


.067342 


140 


15.100 


.066221 


150 


15.352 


.065140 


160 


t 15.603 


.064088 


170 


15.854 


.063072 


180 


16.106 


.062090 


190 


16.357 


.061134 


200 


16.606 


.060210 


210 


16.860 


.059313 


212 


16.910 


.059135 


220 


17.111 


.058442 


230 


17.362 


.057596 


240 


17.612 


.056774 , 


^50 


17.865 


.055975 


260 


18.116 


.055200 


270 


18.367 


.054444 


280 


18.621 


.053710 


290 


18.870 


.052994 


300 


19.121 


.052297 


320 


19.624 


.050959 


340 


20.126 


.049686 


360 


20.630 


.048476 


380 


2L131 


.047323 


400 


21.634 


.046223 


425 


22.262 


.044920 


450 


22.890 


.043686 


475 


23.518 


.042520 


500 


24.146 


.041414 


525 


24.775 


.040364 


550 


25.403 


.039365 


575 


26.031 


.038415 


600 


26.659 


.037510 


650 


27.913 


.035822 


700 


29.172 ' 


.034280 


750 


30.428 


.032865 




Questions and Answers 241 

QUESTIONS AND ANSWERS. 

161. Is a feed water heater an economical factor in the 
equipment of a boiler plant? 

Ans. It certainly is^ provided exhaust steam is used for 
heating. 

162. How many kinds of exhanst heaters are there? 
Ans. TwO;, viz. : Open^ and closed. 

163. Describe in brief terms the action of a so-called 
open heater. 

Ans. The exhaust steam mingles directly with the 
water^ and a portion of it is condensed. 

164. Describe the operation of a closed heater. 

Ans. The exhaust steam and the water are kept sep- 
arate. In some cases the steam passes through tubes that 
are surrounded by water^ and in other types the water 
, fills the tubes that are surrounded by steam. 

165. What difference exists between the two kinds of 
heater ? 

Ans. The closed heater is under full boiler pressure 
when the feed pump is workings while the open heater is 
not because the feed pump is between it and the boiler. 

166. What per cent of saving in fuel may be effected 
by the use of a heater? 

Ans. From 12 to 15 per cent. 

167. Of what capacity should a feed water heater be, 
relative to the boilers ? 

Ans. It should have capacity sufficient to supply the 
boilers for 15 or 20 minutes. 

168. Can the exhaust injector be used for feeding 
; boilers. 

Ans. It can if the boiler pressure does not exceed 75 
pounds. 



242 Steam Engineering 

169. What advantages are gained by the use of mechan- 
ical stokers? 

Ans. Regulation of the supply of fuel to meet the de- 
mand for steam; also the opening and closing of furnace 
doors is avoided. 

170. What are the disadvantages attending the use of 
mechanical stokers? 

Ans, Firsts cost of installation. Second, in case of a 
sudden demand for steam the mechanical stoker cannot re- 
spond as quickly as in hand firing. Third, extra cost for 
power to operate them. 

171. Into how many classes are mechanical stokers 
grouped ? 

Ans. Four. 

172. Enumerate, and briefly describe. 

Ans, Class one — An endless chain of short grate bars 
that travel horizontally over sprocket wheels. 

Class two — Grate bars similar to the ordinary type hav- 
ing a continuous motion up and down, or forward and 
back, the bars being either horizontal or slightly inclined. 

Class three — Grate bars steeply inclined and having a 
slow motion. 

Class four — Under feed stoker in which the coal is pushed 
up onto the grate by mean3 of a revolving screw, or steam 
ram. 

173. In what three forms is mechanical draft used for 
boiler. 

Ans. First — Induced draft. 

Second — Forced draft, in which f^ins force air beneath 
the grates. 



Questions and Answers 243 

Third — A combination of induced and forced draft. 

174. Is a good draft necessary for the efficient opera- 
tion of steam boilers? 

Ans, It certainly is. The economical combustion of 
fuel cannot be accomplished without a good draft. 

175. For what two purposes are chimneys required? 
Ans. Pirst^ to carry off obnoxious gases. Second^ to 

create sufficient draft for the combustion of the fuel. 

176- What factor governs the intensity of the draft, 
independent of the dimensions of the chimney? 

Ans, The difference in weight of the outside and in- 
side columns of air. 

177. What is the best shape of chimney? 
Ans. Eound^ with a straight flue. 

178. What is the weight, and volume of air at a tem- 
perature of 60°, and under average atmospheric pressure 
at sea level? 

Ans. One cubic foot weighs 536 grains, and 13.06 cubic 
feet weigh one pound. 



Care and Operation of Boilers 

Duties. The first act of the engineer on entering his 
boiler-room when he goes on duty should be to ascertain 
the exact height of the water in his boilers. This he can 
do by opening the valve in the drain pipe of the water 
column, allowing it to blow out freely for a few seconds, 
then close it tight and allow the water to settle back in 
the glass. This should be done wdth each boiler under 
steam, not only once, but several times during the day. 
No engineer should be satisfied with a general squint along 
the line of gauge glasses, but he should either go himself, 
or else instruct his fireman, or water tender to make the 
rounds of each boiler and be sure *that the water is all right. 
' The instructions regarding the cleaning of fires, and 
firing, refer particularly to hand fired boilers. Mechani- 
cal stokers will be taken up in their regular order. 

The next thing to be looked after is the fire. If the 
plant is run continuously day and night it is the duty 
of the firemen coming off watch to have the fires clean, 
the ash pits all cleaned out, a good supply of coal on the 
floor, and everything in good order for the oncoming force. 
A good fireman will take pride in always leaving things in 
neat shape for the man who is to relieve him. 

Cleaning Fires. With some varieties of coal this is a 
comparatively easy task, especially if the boilers are fitted 
with shaking grates. With a coal that does not form a 
clinker on the grate bars, the fires can be kept in good 
condition by cleaning them twice or three times in twenty- 

245 



246 Steam Engineering 

four hours^ as the larger part of the loose ashes and non- 
combustible can be gotten rid of by shaking the grates 
and using the slice bar at intervals more or less frequent; 
but such coals are generally considered too expensive to use 
in the ordinary manufacturing plants and cheaper grades 
are substituted. 

Fire Tools. For cleaning fires successfully and quickly, 
the following tools should be provided ; a slice bar^ a fire 
hook, a heavy iron or steel hoe, and a light hoe for clean- 
ing the ash-pit. It is unnecessary to describe these tools, 
as they are familiar to all engineers. A suggestion as to 
the kind of handles with which they should be fitted may be 
of benefit. The working ends of the aforesaid tools having 
been made and each welded to a bar of 1 or 1% inch round 
iron and 10 or 12 inches long^ take pieces of 1 or 1^/4 i^^ch 
iron pipe cut to the length desired f or the handles and weld 
the shanks of the tools to them. To the other end of the 
pipe weld a handle made of round iron somewhat smaller 
than the shank. By using pipe handles the weight of the 
tools is considerably lessened, and they will still be suffi- 
ciently strong. The labor of cleaning the fire will thus be 
greatly lightened. When a fire shows signs of being foul 
and choked with clinker, preparations should be made at 
once for cleaning it by allowing one side to burn down as 
low as possible, putting fresh coal on the other side alone. 
When the first side has burned as low as it can without 
danger of letting the steam pressure fall too much^ take the 
slice bar and run it in along the side of the furnace on 
top of the clinker and back to near the bridge wall^ then 
using the door jamb as a fulcrum, give it a quick strong 
sweep across the fire and the greater part of the live coals 
will be pushed over to the other side. What remains of 



t 



Care and Operation of Boilers 247 



the coal not yet consumed can be pulled out upon the floor 
with the light hoe and shoveled to one side^ to be thrown 
back into the furnace after the clinker is taken out. Hav- 
ing now disposed of the live coal^ take the slice bar and 
run it along on top of the grates^ loosening and breaking 
up the clinker thoroughly^ after which take the heavy hoe 
and pull it all out on the floor. A helper should be ready 
with a pail of water^ or^ what is still better^ a small rubber 
hose connected to a cold water pipe running along the 
boiler fronts for this purpose, and put on just enough 
water to quench the intense heat of the red hot clinker as it 
lies on the floor. When the grates are cleaned, close the 
door, and with the slice bar in the other side push all the 
live coal over to the side just cleaned, where it should be 
leveled off and fresh coal added. After this has become 
ignited, treat the other side in the same way. An expert 
fireman will thus clean a fire with very little loss in steam 
pressure, and practically no waste of coal. 

Disposal of the Ashes, The problem of disposing of the 
ashes in large power plants is quite a serious one, and any 
device that tends to lessen the cost of labor, and shorten the 
time consumed in conveying the ashes from the boiler 
Toom certainly merits the attention of chief engineers. 

The suction conveyor system of the Darley Engineering 
'Company, Chicago, a general view of which is shown in 
^Fig. 97, consists essentially of four parts, as follows: 

1. Conveyor Pipe. 

3. Separator. 

3. Exhauster. 

4. Water Jet. 

The conveyor pipe line is made in three sizes and ca- 
pacities, namely, 6", 8" and 10", of iron or steel pipe. The 



248 



Steam Engineering 




Fig. 97 

diagram showing a complete suction conveyor system as 

applied to handling ashes itrom boilers 

conveyor pipe, as far as. possible, is run in straight lines. 
It is generally placed beneath the surface, but can be ele- 
vated or run anywhere to suit conditions. 



Care and Operation of Boilers 



249 



The separator, which is in reality an expansion cham- 
ber, also serves as a storage tank for storing the conveyed 
material. This separator is always placed at the end of 
the conveyor run. It serves to catch the material conveyed 
and hold it until it can be drawn (by gravity through an 




Fig. OS 

ASH CONVEYOR EXHAUSTER SET DRIVEN BY STEAM TURBINE 

under-cut gate) into cars, carts or barges. This separator 
is located in the most convenient position for the purpose. 
The separator can be made any size, to hold any predeterm- 
ined amount of material, or for a time run of the conveyor 
of any fixed duration. These separators can also be mount- 



250 



Steam Engineering 



tional bin storage capacity is required. Separators are gen- 
erally built of cylindrical form and of steel plate construc- 
tion with a cone top and bottom. For certain work and on 
small sized plants^ they can be made rectangular^ or of an 
irregular shape. They can also be made of concrete^ either 
square or rounds with small cone top of steel plate. They 
are always made water tight. 




Fig. 99 
ash conveyor exhauster set driven by induction motor 



The Exhauster (Figs. 98 and 99) consists essentially of 
a rotating impeller^ surrounded by a suitable case^ with an 
intake air opening at the center^ and a discharge opening 
at the circumference. In appearance^ it is similar to the 
centrifugal pump. The efficiency depends largely upon 
the design of the impeller and casing, and on the proper 
•shaping of these parts. In actual practice some conditions 
call for other types. For instance, for a small, simple lay* 



Care and Operation of Boilers 251 

out, an ordinary exhaust fan can be used, whereas for cer- 
tain complicated and extensive work, a cycloidal blower is 
best adapted for the purpose. It can be either steam, or 
motor driven for alternating or direct current. These ma- 
chines are very strong in construction, and will operate 
under adverse conditions with a very low cost for main- 
tenance, and -are especially suitable for this class of work. 

Just before entering the separator, the conveyed mate- 
rial passes through a water jet, located in the conveyor 
pipe. This jet is composed of %^' holes, spaced 1" cen- 
ters, and serves two purposes, viz., it takes the heat out 
of the hot material, such as ashes, etc., and eliminates all 
dust when the material is dusty. In this way all dust is 
kept out of the exhauster. 

In the case of an ashes conveyor, the intakes are placed 
in front of the ash pits of the boilers, or at any other de- 
sired place, and the ashes are hoed or shoveled from the 
ash pits into these intakes, whence they disappear through 
the pipe line at a higher velocity. The conveyor pipe line 
will take them away as fast as they are fed to the intakes. 
When not in use, a cast iron cover is placed over these 
intakes. These covers are lifted off when material is to be 
fed to the conveyor. 

The size of the intake opening is slightly smaller in diam- 
eter than that of the pipe line, so that any piece of material 
that passes the intake opening will be conveyed freely 
through the conveyor pipe. 

As the hardest wear comes on the elbows, a patented 
split elbow is used, having an interchangeable wearing back, 
about 3'' thick, made of hard iron. These wearing backs 
will last from 10 to 18 months, and are quickly replaced 
when worn out, and can be replaced without interfering 



252 



Steam Engineering 



with the 'working of the convej^or, and at trifling cost. 
Patented fittings with interchangeable wearing back are 
also used when required. 

Owing to the higher velocity of the air in the central 
portion of the pipe^ the tendency is to convey the material 
in suspension in the center of the pipe. That this is a fact 




Fig. 100 
exhauster set driven by direct current motor 



can be readily seen on looking into a conveyor pipe in 
operation. 

This fact prevents serious wear on the pipe^, and from 
observation of plants in use up to two and one-half years, 
shows that an ordinary steel pipe, handling ashes, will last 
for years. 

No material' comes in contact with any moving part of 
this conveyor, and it is dustless in operation. These facts 



Care and Operation of Boilers 253 

should appeal to engineers^ especially those who have had 
experience with mechanical conveyors in handling ashes. 

There is absolutely no corrosion of the conveyor pipe^ 
as the great rush of air through the pipe keeps same per- 
fectly dry under all conditions. 

The following table gives capacities^ etc. : 
with convenient accessories for manipulation. 

Size of Capacity- 

Conveyor, per minute. 

6" ' 200 lbs. 

8" 300 lbs. 

lO;; ; 500 lbs. 

Firing. No definite set of rules for hand firing can be 
laid down that will be suitable for all steam plants^, or for 
the many different kinds of coal used. Some kinds of coal 
need very little stirring or slicing^ while others that have 
a tendency to coke^ and form a crust on top of the fire need 
to be sliced quite often. 

Every engineer^ if he is at all obs^rvant^ should be able 
to judge for himself as to the best method of treating the 
coal he is using^ so as to get the most economical results. A 
few general maxims may be laid down. Firsts keep a clean 
fire; second^ see that every square inch of grate surface is 
covered with a good live fire ; third;, keep a level fire, don't 
allow hills and valleys, and yawning chasms to form in the 
furnace, but keep the fire level; fourth, when cleaning the 
fire always be sure to clean all the clinkers and dead ashes 
away from the back end of the grates at the bridge wall, 
in order that the air may have a • free passage through the 
grate bars, because this is one of the best points in the fur- 
nace for securing good combustion, provided the bridge 
wall is kept clean from the grates up. 



254 Steam Engineering 

By keeping the back ends of the grate bars and the face 
of the bridge wall clean^ the air is permitted to come in 
contact with the hot fire brick^ and thus one of the greatest 
aids to good combustion is utilized. Don^t allow the fire 
to become so deep and heavy that the air cannot pass up 
through it^ because without a good supply of air good com- 
bustion is impossible. When the chimney draft is good the 
-quality of cold air admitted underneath the grate bars may 
be easily regulated by leaving the ash-pit doors partly open. 

The amount of opening required can be ascertained by a 
little experimenting and depends upon the intensity of 
ihe drafts and the condition of the fire. With a clean, light 
iire, and the air spaces in the gates free from dead ashes, a 
^slight opening of the ash-pit doors will suffice to admit all 
ihe air required beneath the grates. But if the fire is 
heavy and the grates are clogged, a larger opening will be 
necessary. In firing bituminous coal containing a large 
3)ercentage of volatile (light or gaseous matter), the best 
results can be obtained by leaving the fire doors slightly 
open for a few seconds immediately aftei throwing in a 
fresh fire. The reason for doing this is that the volatile 
matter in the coal flashes into flame the instant it comes 
in contact with the heat of the furnace, and if a sufficient 
supply of oxygen is not present just at this particular time 
the combustion will be imperfect, and the result will be 
the formation of carbon monoxide or carbonic oxide gas, 
.and the loss of about two-thirds of the heat units contained 
in the coal. This loss can be guarded against in a great 
measure by a sufficient volume of air, either through the 
fire doors directly after putting in a fresh fire, or what is 
still better, providing air ducts through the bridge wall or 
«ide walls which will bring the air in on top of the fire. 



II 



Care and Operation of Boilers 255 

Each pound of coal requires for its complete combustion 
12 pounds^ or about 150 cubic feet of air, and the largest 
volume of air is needed just after fresh coal has been added 
to the fire. 

Cleanliness. In order to get the best results, great care 
should be taken that the tubes be kept clean and free from 
soot. Especially does this apply to horizontal return tubu- 
lar boilers, for the reason that when the tubes become 
clogged with soot the efficiency of the draft is destroyed^ 
and the steaming capacity of the boiler is greatly reduced. 
Soot not only stops the draft, but it is a non-conductor of 
heat. In some batteries of boilers where an inferior grade 
of coal is used and the draft is poor, it is absolutely neces- 
sary to scrape or blow the tubes at least once a day in order 
to enable the boilers to generate sufficient steam. 

As to the process of cleaning there are various devices on 
the market, both for blowing the soot out by means of a 
steam jet and also for scraping the inside of the tubes. 
The steam jet, if properly made and used with a high 
pressure and dry steam, does very satisfactory work, but 
is should not be depended upon exclusively to keep the 
tubes clean, because in process of time a scale will form in- 
side the tubes that nothing but a good scraper will remove. 
For that reason it is good practice to use the scraper two 
or three times a week at least. When the boiler is cooled 
down for washing out, the bottom of the shell should be 
cleaned of all accumulations of dust and ashes, the com- 
bustion chamber, back of the bridge wall cleaned out, and 
the back flue sheet or head swept off and examined, and if 
there is a fusible plug in the back head the scale should be 
scraped from it, both inside and outside the boiler, because 
if it is covered with scale, neither the water, nor the heat 
can come in contact with it, and it will be non,-effective. 



256 Steam Engineering 

Washing Out. The length of time that a boiler can be 
run safely and economically after having been washed out 
depends upon the nature of the feed water. If the water 
is impregnated to a considerable extent with scale forming 
matter, the boiler should be washed out every two weeks 
at the least, and in some cases of particularly bad water it 
becomes necessary to shorten the time to one week. To 
prepare a boiler for washing the fire should be allowed to 
burn as low as possible and then be pulled out of the 
furnace, the furnace doors left slightly ajar, and the damper 
left wide open in order that the walls may gradually cool. 
It is as bad a practice to cool a boiler off too suddenly as 
it is to fire it up too quick, because the sudden change of 
temperature either way has an injurious effect on the seams, 
contracting or expanding the plates, according as it is 
cooled or warmed, and thus creating leaks and very often 
small cracks radiating from the rivet holes, and becoming 
larger with each change of temperature, until finally the 
strength of the steam is destro^^ed and rupture takes place. 
After the boiler has become comparatively cool and there is 
no pressure indicated by the steam gauge the blow off cock 
may be 'opened and the water allowed to run out. The 
gaug.e cocks, and also the drip to the water column should 
be left open to allow the air to enter and displace the water. 
Otherwise there will be a partial vacuum formed in the 
boiler and the water will not run out freely. 

A boiler should not be blown out, that is, emptied of 
water while under pressure. The sudden change of tem- 
perature is sure to have a bad effect upon the sheets and 
seams. Suppose for instance that all the water is blown 
out of a boiler under a pressure of 20 pounds by the steam 
gauge. The temperature of steam at 20 pounds is 260° F., 



Care and Operation of Boilers 257 

and it may be assumed that the metal of the boiler is at or 
near that temperature also. Assume the temperature of 
the atmosphere in the boiler-room to be 60° F. There will 
then be a range of 260° — 60° =200° temperature for the 
boiler to pass through within a short time, which will cer- 
tainly have a bad effect, and besides this the boiler shell will 
be so hot that the loose mud and sediment left after the 
water has run out is liable to be baked upon the sheets, 
making it much harder to remove. 

While inside the boiler the boiler washer should closely 
examine all the braces and stays, and if any are found 
loose or broken they should be repaired at once before the 
boiler is used again. The soundness of braces, rivets, etc., 
can be ascertained by tapping them with a light hammer. 

Renewing Tubes. As it is practically impossible to pre- 
vent scale from forming on the outside of the tubes of 
horizontal tubular boilers unless the feed water is expection- 
ally good, and as the tubes will in course of time become 
leaky where they are expanded into the heads, the engineer 
if he has a battery of two or more, should take advantage 
of ihe first opportunity that presents itself to take out of 
service the boiler that shows the most signs of deterioration 
and take out the tubes, and after cleaning them of scale by 
scraping and hammering or rolling in a tumbling cylinder, 
he should select those that are still in good condition and 
have them pieced out at the ends, making them almost as 
good as new. 

All tube failures reduce to four classes : 

(1) Pitting, which causes pin holes to be formed. 

(2) Defective welds, which cause the tube to open, as 
in A, Fig. 101. 



258 



Steam Engineering 



(3) An initial bagging resulting in a rupture, as in B. 

(4) Scabbing and blistering^ as in C. 

In the first case the tube is not enlarged, and may be 
drawn through a tube sheet, without disturbing other tubes, 
though usually with diflBculty, owing to deposits on the 
outer surface. 




Fig. 101 
photogeaphs showing distention of tubes at point of 

RUPTURE 



In the other cases, the tubes become larger than their 
original size, hence they cannot be drawn through the tube 
sheet, water-leg or header, unless they are split and collapsed 
inch by inch for their entire length beyond the point of 
failure, and if they also pass through cross baffles the en- 
largement will pull out the bricks and destroy the baffle. 



Care and Operation of Boilers 259 

To remove a tube in this way is the work of days, and in 
consequence the actual method used is to cut out all tubes 
— numbering at times half a dozen below the defective one 
— and to avoid destroying the baffles these tubes are cut into 
several pieces. 

In case the tubes are all taken out of the boiler for 
repairs the boiler washer will have a good opportunity to 
thoroughly clean the inside of the boiler, and if there are 
any loose rivets they should be replaced and leaky or sus- 
picious looking seams chipped and caulked. If there are 
indications of corrosion or pitting, a stiff paste or putty 
made of plumbago mixed with a small proportion of cylin- 
der oil may be applied to the affected parts with good 
results. 

Feed Water, There is no steam plant of any consequence 
that does not have more or less exhaust steam, or returns 
from a steam heating system, which can be utilized for 
heating the feed water before it enters the boiler. Cold 
water should never be pumped into a boiler that is under 
steam when it is possible to prevent it. 

In feeding a boiler the speed of the feed pump should 
be so gauged as to supply the water just as fast as it is 
evaporated. The firing can then be even and regular. 

If the supply of feed water should suddenly be cut oflP, 
owing to breakage of the pump or bursting of a water main, 
and no other source of supply was available, the dampers 
should be immediately closed, or if there should be no 
! damper in the breeching, the draft may be stopped by 
i opening the flue doors. The fires should then be deadened 
I by shoveling wet or damp ashes in on top of them, or if the 
! ashes cannot be readily procured, bank the fires over with 
! green coal broken into fine bits. This, with the draft all 



260 Steam Engineering 

shut off^ will deaden the fires^ while the engine still running 
will gradually use up the extra steam. If the water should 
get dangerously low in the boilers the fires may be pulled, 
provided they have become deadened sufficiently, but they 
should never be pulled while they are burning lively, be- 
cause the stirring will only serve to increase the heat, and 
the danger will be aggravated. 

Connecting a Recently Fired Up Boiler. After a boiler 
has been washed out, filled with water, and fired up, the 
next move is to connect it with the main battery. The 
steam in the boiler to be connected having been raised to 
the same pressure as that in the battery, the connecting 
valve should be opened slightly, just enough to permit a 
smdil jet of steam to pass through, which can be heard by 
placing the ear near the body of the valve. This jet of 
steam may be passing from the battery into the newly con- 
nected boiler, or vice versa. Whichever way it passes, the 
valve should not be opened any farther until the flow of 
steam stops, which will indicate that the pressure has been 
equalized. It will then be found that the valve will move 
much easier, and it may be gradually opened until it is 
wide open. 

Foaming. Water carried with the steam from the boiler 
to the engine, even if in small quantities, is very detri- 
mental to the successful operation of the engine, as it 
washes the oil from the walls of the cylinder, thereby in- 
creasing the friction, and unless a plentiful supply of oil 
is entering the cylinder, cutting of the piston rings will 
take place. There is also danger of breaking a cylinder 
head, or of bending the piston rod if the water conies in too 
large quantities. 



Care and Operation of Boilers 261 

There are certain kinds of water which have a natural 
tendency to foam, especially such as contain considerable 
organic matter, and the more severe the service to which 
the boiler is put the more will the water foam, until it is 
practically impossible to locate the true level of the water 
in the boilers, and the only recourse the water tender has 
is to keep his feed pump running at such a speed as will, 
in his judgment supply the water as fast as it goes out of 
the boilers. It is a dangerous condition to say the least, 
and the only remedy for it is either a change to a different 
kind of water, or if this is not possible, then an increase in 
the number of boilers, which would make it possible to 
supply sufficient steam for the engine without being com- 
pelled to fire the boilers so hard. 

Priming. By which is meant the carrying over of water 
in the form of fine spray mingled with the steam, is not so 
dangerous as foaming and yet it causes much loss in the 
efficiency of a boiler or engine. It can be prevented to a 
large extent by placing a baffle plate in the steam space of 
the boiler directly under the dome or outlet to the connec- 
tion with the steam main. 

The following rules are compiled from those issued by 
various boiler insurance companies in this country and 
Europe — they apply to all boilers except as otherwise noted : 

1. Safety Valves. Great care should be exercised to 
see that these valves are ample in size and in working order. 
Overloading , or neglect frequently leads to the most dis- 
astrous results. Safety valves should be tried at least 
once every day to see that they will act freely. 

2. Pressure Gauge. The steam gauge should stand at 
zero when the pressure is off, and it should show the same 
pressure as the safety valve when that is blowing off. If 



262 Steam Engineering 

not, then one is wrong, and the gauge should be tested by 
one known to be correct. 

3. Water Level. The first duty of an engineer before 
starting, or at the beginning of his watch, is to see that 
the water is at the proper height. Do not rely on glass 
gauges, floats or water alarms, but try the gauge cocks. 
If they do not agree with water gauge, learn the cause and 
correct it. Water level in Babcock & Wilcox boilers should 
be at center of drum, which is usually at middle gauge. 
It should not be carried above. 

4. Gauge Cocks and Water Gauges must be kept clean. 
Water gauge should be blown out frequently, and the glasses, 
and passages to gauge kept clean. The Manchester, Eng- 
land, Boiler Association attributes more accidents to in- 
attention to water gauges than to all other causes put to- 
gether. 

5. Feed Pump, or Injector, These should be kept in 
perfect order, and be of ample size. No make of pump can 
be expected to be continuously reliable without regular and 
careful attention. It is always safe to have two means of 
feeding a boiler. Check valves, and self-acting feed valves 
should be frequently examined and cleaned. Satisfy your- 
self that the valve is acting when the feed pump is at work. 

6. Low Water. In case of low water, immediately cover 
the fire with ashes (wet if possible) or any earth that may 
be at hand. If nothing else is handy use fresh coal. Draw 
fire as soon as it can be done without increasing the heat. 
Neither turn on the feed, start or stop engine, nor lift 
safety valve until fires are out, and the boiler cooled down. 

7. Blisters and Grades. These are liable to occur in 
the best plate iron. When the first indication appears there 
must be no delay in having it carefully examined and 
properly cared for. 



Care and Operation of Boilers 263 

8. Fusible Plugs, when used^ must be examined when 
the boiler is cleaned^ and carefully scraped clean on both 
the water and fire sides^, or they are liabk not to act. 

9. Firing, Fire evenly and regularly^ a little at a time. 
Moderately thick fires are most economical^ but thin firing 
must be used where the draught is poor. Take care to keep 
grates evenly covered^ and allow no air-holes in the fire. 
Do not "^^clean^^ fires oftener than necessary. With bi- 
tuminous coal^ a ^^coking fire/^ i. e.^ firing in fronts and 
shoving back when coked, gives best results, if properly 
managed. 

10. Cleaning. All heating surfaces must be kept clean 
outside and in, or there will be a serious waste of fuel. The 
frequency of cleaning will depend on the nature of fuel 
and water. As a rule, never allow over -^^ inch scale or soot 
to collect on surfaces between cleanings. Hand-holes should 
be frequently removed, and surfaces examined, particularly 
in case of a new boiler, until proper intervals have been 
established by experience. 

Water tube boilers are provided with extra facilities for 
cleaning, and with a little care can be kept up to their 
maximum efficiency, where tubulars, or locomotive boilers 
would be quickly destroyed. For inspection, remove the 
hand-holes at both ends of the tubes, and by holding a 
lamp at one end and looking in at the other, the condition 
of the surface can be fully seen. Push the scraper through 
the tube to remove sediment, or if the scale is hard use the 
chipping scraper made for that purpose. Water through 
a hose v/ill facilitate the operation. In replacing hand- 
hole caps, clean the surfaces without scratching or bruising, 
smear with oil, and screw up tight. Examine mud-drum 
and remove the sediment therefrom. 



264 Steam Engineering 

The exterior of tubes can be kept clean by the nse of 
blowing pipe and hose through openings provided for that 
purpose. In using smoky fuel^ it is best to occasionally 
brush the surfaces when steam is off. 

11. Hot Feed-Water, Cold water should never be fed 
into any boiler when it can be avoided^ but when necessary 
it should be caused to mix with the heated water before 
coming in contact with any portion of the boiler. 

12. Foaming. When foaming occurs in a boiler, check- 
ing the outflow of steam will usually stop it. If caused by 
dirty water, blowing down and pumping up will generally 
cure it. In cases of violent foaming, check the draft and 
fires. 

. 13. Air LeaTcs, Be sure that all" openings for admission 
of air to boiler or flues, except through the fire, are care- 
fully stopped. This is frequently an unsuspected cause of 
serious waste. 

14. Bloiving Of. If feed-water is muddy or salt, blow 
off a portion frequently, according to condition of water. 
Empty the boiler every week or two, and fill up afresh. 
When surface blow-cocks are used, they should be often 
opened for a few minutes at a time. Make sure no water 
is escaping from the blow-off cock' when? it is supposed to 
be closed. Blow-off cocks, and check-valves should be ex- 
amined every time the boiler is cleaned. 

15. Leahs. When leaks are discovered, they should be 
repaired as soon as possible. 

16. Bloiving Of for Washing. Never empty the boiler 
while the brickwork is hot. 

17. Filling Up. Never pump cold water into a hot 
boiler. Many times leaks, and, in shell boilers, serious 
weaknesses, and sometimes explosions are the result of 
such an action. 



Care and Operation of Boilers 265 

18. Dampness. Take care that no water comes in con- 
tact with the exterior of the boiler from any cause^, as it 
tends to corrode and weaken the boiler. Beware of all 
dampness in seatings or coverings. 

19. Galvanic Action. Examine frequently parts in con- 
tact with copper or brass^ where water is present, for signs 
of corrosion. If water is salt or acid, some metallic zinc 
placed in the boiler will usually prevent corrosion, but it- 
will need attention and renewal from time to time. 

20. Rapid Firing. In boilers with thick plates, or 
seams exposed to the fire, steam should be raised slowly, 
and rapid or intense firing avoided. With thin water tubes, 
however, and adequate water circulation, no damage can 
come from that cause. 

21. Standing Unused. If a boiler is not required for 
some time, empty and dry it thoroughly. If this is im- 
practicable, fill it quite full of water, and put in a quantity 
of common washing soda. External parts exposed to damp- 
ness should receive a coating of linseed oil. 

22. General Cleanliness. All things about the boiler 
room should be kept clean and in good order. Negligence 
tends to waste and decay. 

Miscellaneous. In burning coal under a boiler, it shouid 
be remembered that the object is to transfer as many as 
possible of the total heat units^ contained in the coal to the 
water in the boiler, and that any failure to do this shows a 
lack of engineering ability. 

No leak or waste is too small to deserve attention and 
unceasing viligance is the price of economy. The grates, if 
hand-fired, should be of standard shaking pattern, and the 
fire kept thin enough so that it can be kept clean and bright 
without too much overhead slicing. Every time that the 



266 Steam Engineering 

furnace door is opened for the introduction of coal or for 
cleaning the fire in any way, there is a distinct loss of 
efficiency on account of the inrush of cold air. Most 
boiler-room fires suffer from too much meddling. It is 
undoubtedly better in all plants of any size to install me- 
chanical stokers, there being the double advantage of a 
uniform feed of fuel, and a definite air supply, just suffi- 
cient to maintain combustion. 

HEATING SURFACE. 

For a fire-box boiler of the vertical type, the area of the 
flue sheets minus the sectional area of the flues, plus the 
area of the fire-box plus the inside area of the flues consti- 
tutes the heating surface. If the boiler is a horizontal in- 
ternally fired boiler, the heating surface will consist of, 
first, area of three sides of the fire-box ; second, area of the 
crown sheet; third, area of flue sheets minus sectional area 
of flues ; fourth, inside area of the flues. 

In estimating the area of the fire-box, the area of the fire 
door should be subtracted therefrom. If the fire-box be 
circular, as in the case of a vertical boiler, the area may 
be obtained by first finding by measurements the diame- 
ter, which multiplied by 3.1416 will give the circumfer- 
ence. Then multiply this result by the height or the dis- 
tance between the grate bars and the flue sheet. In the 
case of water tube boilers the outside area of the tubes 
must be taken. Two examples will be given illustrating 
methods of calculating heating surface: 

First, take a horizontal tubular boiler, diameter 72 in., 
length 18 ft., having sixty-two 4% in, flues: find area of 
lower half of shell. 



Care and Operation of Boilers 267 

Circumference=diameterX 3.1416=18.8496 ft. 

One-half of the circumference multiplied by the length 
zizrequired area. Thus, 18.8496-f-2X 18=169.64 sq. ft. 

Next find heating surface of back head below the water 
line. Total area=722X. 7854=4071.5 sq. in. Assume 
two-thirds of this area to be exposed to the heat, 2/3 of 
4071.5=2714.3 sq. in. Prom this must be deducted the 
sectional area of the tubes. In giving the size of boiler 
tubes the outside diameter is taken. The tubes being 4% 
in.; the area of a circle 4% in. in diameter is 15.9 sq. in. 
Number of flues, 62X15.9^985.8 sq. in.=sectional area 
of tubes. The heating surface of the back head therefore= 
3714.3—985.8=1728.5 sq. in. Dividing this by 144, to 
reduce to feet, we have 12 sq. ft. 

Next find inside area of tubes. The standard thickness 
of a 41/^ in. tube=.134 in. The inside diameter therefore 
will be 4.5 — (2X. 134) =4.23 in., and the circumference 
will be 4.23X3.1416=13.29 in., and the inside area will be 
13.29Xlength, 18 ft.,=216 in. Thus 216X13.29^144= 
19.93 sq. ft., inside area of one flue. There being 62 flues, 
the total heating surface of tubes is 19. 93X62:=1235. 66 
sq. ft. The heating surface of the front head is found in 
the same manner as that of the back head, with the excep- 
tion that the whole area should be figured instead of two- 
thirds, for the reason that the entire surface is exposed to 
the heat, although that portion above the water line may 
be considered as superheating surface. The heating surface 
of front head would be: area 4071.5 — sectional area of 
tubes 985.8=3085.7 sq. in.=21.43 sq. ft. 

The total heating surface of the boiler is thus found to 
be 1438.73 sq. ft., divided up as follows: 



268 Steam Engineering 

Lower half of shell, 169.64. sq. ft. 

Back head, 12.00 sq. ft. 

Tubes, 1235.66 sq. ft. 

Front head, 21.43 sq. ft. 

1438.73 sq. ft. 

Next taking a vertical fire-box boiler of the following 
dimensions : diameter of flue sheet, and also of fire-box, 50 
in. ; height of fire-box above grate bars, 30 in. ; number of 
flues, 200; size of flues, 2 in.; length of flues, 7 ft. 

First, find heating surface in flue sheet. 

Area of circle, 50 in. in diameter= 1,963.5 sq. in. 

Sectional area of 2 in. flue=3.14 sq. in., which multi- 
plied by 200=628 sq. in., total sectional area of tubes. The 
heating surf ace of one flue sheet therefore will be 1,963.5 — 
628-M44=9 sq. ft. 

Assuming that the tops of the flues are submerged, the 
area of the top flue sheet will also be 9 sq. ft. Then heating 
surface of flue sheets=9X^=18 sq. ft. 

Second, find heating surface of tubes. The standard 
thickness of a 2 in. flue is .095 in. The inside diameter 
will consequently be 2 — (.095X^)=1.8 in., and the cir- 
cumference will be 1.8X3.1416=5.66 in. The length of 
the flue being 7 ft., or 84 in., the inside area will be 5.66 X 
84-f-144=3.3 sq. ft., and multiplying this result by 200 we 
have 200X3.3=660 sq. ft. as the heating surface of the 
flues. 

Third, find heating surface of the fire-box. Diameter of 
fire-box=50 in., which multiplied by 3.1416=157.08, which 
is the circumference. The height being 30 in., the total 
area will be 157.08X30^144=32.7 sq. ft. Allowing 1 sq. 
ft. as the area of the fire door, will leave 31.7 sq. ft. heating 



Care and Operation of Boilers 269 

surface of fire-box. The heating surface of the boiler 
will be: 

For the flue sheets, 18 sq. ft. 

For the flues, 660 sq. ft. 

For the flre-box, 31.7 sq. ft. 



Total, 709.7 sq. ft. 

The above methods may be applied in estimating the 
heating surface of any boiler, provided in the case of water 
tube boilers that the outside in place of the inside area of 
the tubes be figured. 

Reducing Loss in Handling Coal, In large coal-hand- 
ling systems used in power plants of considerable capacity, 
there is often a chance to save a few dollars in operation if 
the station staff is on the alert to cut down wastes. In a 
good sized plant there are frequently several hundred con- 
veyer buckets to be driven, and a twenty or twenty- five 
horse-power engine, or motor may be needed to operate the 
system at its full capacity. With the most careful lubrica- 
tion and skilled attention, the friction load of the conveyer 
system may amount to forty or fifty per cent of the power 
required when operating with the buckets full. If care is 
not taken- to shut down the conveyer promptly after the 
delivery of coal to the bunkers or when the collection of 
ashes has ceased, the power loss may be felt in the yearns 
operating expense of the auxiliaries. 

The operation of the endless conveyer chain, empty, once 
or twice a week for purposes of oiling or greasing may cost 
perhaps ten dollars a year for the extra power used, com- 
pared with lubricating when the conveyer is handling fuel. 
In larger conveyer installations two men are often needed 
to apply the oil or grease as each bucket passes by, a third 



270 Steam Engineering 

man being on hand to fill the cans. If this work can be 
arranged to be done when the conveyer is delivering coal, 
a desirable gain will be made, since there are always points 
in the travel of the conveyer belt or buckets where they are 
empty and thus readily inspected in detail, or oiled in any 
part. 

Two other frequent sources of waste in the handling of 
a coal-conveyor system are, in the pocket lights, and the 
steam lines which may be in use. Current is wasted through 
failure to cut off the incandescents as soon as they are not 
needed in the recesses of the pocket, and when several 
steam-pipe branch lines are used in connection with hoist- 
ing engines, if a main valve is not installed at the entrance 
of the pocket or tower, leakages in the separate valves are 
liable to prove expensive. 

QUESTIONS AND ANSWERS. 

179. What is one of the most important duties of the 
engineer when he goes on watch ? 

Ans. To ascertain the exact height of the water in his 
boilers. 

180. Describe the correct method of doing this. 

Ans. Open the valve in the drain pipe of the water col- 
umn, and allow the water to blow out freely for a few 
seconds, then close the valve and note the level of the water 
when it settles back in the gauge glass. 

131. What is the next important step in beginning the 
day^s work ? 

Ans, To see that the fires are cleaned, and in good con- 
dition. 

182. In firing boilers by hand, what is the first and 
most important rule to be observed ? 



{Questions and Answers 271 

Ans. Keep a clean fire. 

183. What is the second rule? 

Ans, See that every square inch of grate surface is 
covered with a good live fire. 

184. Give the third rule regarding firing by hand. 
Ans, Keep a level fire. 

185'. What is the fourth rule? 

Ans. When cleaning the fire, always clean all clinkers 
and dead ashes away from the back end of the grates and 
the bridge wall. 

1-86. Why should this be done ? 

Ans. In order to allow a free passage of the air through 
the grate bars, so as to promote combustion. 

187. If the plant runs continuously, day and night, 
what is one of the important duties of the fireman coming 
off watch? 

Ans. To leave clean fires, clean ash pits, and a good 
supply of coal ready for the oncoming force. 

188. How long a time should the fires be allowed to 
burn before cleaning? 

Ans. This depends upon the quality of the coal. With 
a coal that does not clinker on the grate bars, an interval 
of 7 or 8 hours may elapse between cleanings, but with the 
average soft coal the fires should not be allowed to burn 
longer than 4 or 5 hours without cleaning. 

189. What is one of the greatest aids to good combustion 
in a hand-fed furnace? 

Ans. A clean bridge wall, kept as hot as possible. 

190. What precautions should be observed regarding 
the depth of the fire? 

Ans. It should not be allowed to become so deep and 
heavy as to prevent the air from passing up through it 
freely 



272 Steam Engineering 

191. How should the position of the ash-pit doors be 
regulated ? 

Ans, With a clean^ light fire^ a slight opening will be 
sufficient^ but with a heavy fire^ and the grates clogged with 
ashes, a larger opening is necessary. 

192. How can the best results be secured in firing 
bituminous coal ? 

Ans. By leaving the fire doors slightly open for a few 
seconds immediately after throwing in a fire. 

193. What reason is there for doing this? 

Ans. Because the volatile matter in the coal flashes into 
flame the instant it comes in contact with the heat of the 
furnace, and unless there is sufficient supply of oxygen 
present just then, the combustion will be imperfect. 

194. What is the result of this imperfect combustion? 

Ans. The formation of carbonic oxide gas, and -the con- 
sequent loss of about two-thirds of the heat units contained 
in the coal. 

195. How may this loss be prevented in a great meas- 
ure? 

Ans. By admitting a ^sufficient volume of air, either 
through the fire doors, directly after throwing in a fresh 
fire, or, better still, providing air ducts through the bridge 
wall, or side walls, which will direct the air in on top of 
the fire. 

196. How much air is required for the complete com- 
bustion of one pound of coal? 

Ans. By weight 12 pounds — by volume 150 cubic feet. 

197. What precaution is necessary regarding the tubes 
of a boiler in order to get the best results from the fuel ? 

Ans. The tubes should be kept clean and free from soot 
and scale. 



Questions and Answers 273 

198. Should the steam jet cleaner be depended upon 
alone for cleaning the tubes? 

Ans, No. The scraper should also be used. 

199. How should safety valves be looked after? 

Ans. They should be ample in size^ never overloaded, 
and should be tested at least once a day to see that they 
act freely. 

200. At what point should the steam gauge pointer 
stand when the pressure is off ? 

Ans. It should stand at zero. 

201. What should be done in case of low water in a 
boiler ? 

Ans, The fire should be covered immediately with ashes, 
earth, or if neither is available use fresh coal. Draw the 
fire as soon as it can be done without increasing the heat. 

202. Should the rate of feeding the water be increased, 
in case of extremely low water in the boiler? 

Ans. It should not, neither should the engine be stopped 
or the safety valve lifted, until the fires are out, and the 
boiler cooled down. 

203. In case of indications of cracks or blisters appear- 
ing on the boiler sheets, what should be done ? 

Ans. There shomld be no delay in making repairs. 

204. What should be done with fusible plugs when used ? 
Ans. They should be cleaned and carefully scraped on 

both water and fire sides at each washing out. 

205. How may the most economical, results regarding 
fuel be attained with a steam boiler ? 

Ans. By keeping the heating surfaces clean, both inside 
and outside, also careful firing, a little at a time, but keep- 
ing the grates covered. 

2^)6. Should cold water ever be fed into a boiler when 
it is under pressure ? 



274 Steam Engineering 

Ans, Not when it can be avoided. 

207. How may foaming nsnally be stopped? 

Ans, By checking the outflow of steam, by blowing 
down and pumping up, or by checking the draft and fires. 

208. Should air be allowed to pass to the boiler or tubes, 
except through the furnace ? 

Ans. It should not, as it will cause a waste of fuel. 

209. What should be done with leaks when discovered? 
Ans. They should be repaired as soon as possible. 

210. What precautions should be observed when pre- 
paring to empty a boiler for washing out, or other pur- 
poses? 

Ans. Allow it to cool down until there is no steam pres- 
sure, and until the brick work is cool also. 

211. When firing up a boiler what course should be 
pursued ? 

Ans. Steam should be raised very slowly, and rapid fir- 
ing avoided. 

212. What bad results follow too rapid firing up of a 
boiler ? 

Ans. Straining of the joints and seams eaused by un- 
equal expansion. 

213. What should be done with a boiler that is to 
stand idle for any length of time? 

Ans. It should be emptied, and thoroughly dried. In 
case this is impracticable, fill it full of water, and put in 
a quantity of washing soda. 

214. How long a time may a boiler be safely operated 
between dates of washing out ? 

Ans. This depends upon the nature of the feed water. 
The time should never be longer than two weeks, and with 
very bad water, the boiler should be washed out once a 
week. 



Questions and Answers 275 

215. Besides cleaning the boiler inside, what other very 
important work should the boiler washer perform while 
inside the boiler ? 

Ans. He should closely examine all braces, stays, and 
rivets by tapping them with a hammer. Any loose or de- 
fective parts can usually be detected in this way. 

216. Describe four ways in which tube failures may 
occur. 

Ans, 1. Pitting. 2. Defective welds. 3. Bagging. 4. 
Scabbing and blistering. . 

217. How may a great saving in fuel be effected with 
regard to the feed water ? 

Ans. By heating it with the exhaust steam from engines 
and pumps before passing it to the boilers. 

218. Describe the available heating surface of a station- 
ary boiler, of either type, return tubular or water tube. 

Ans. The lower half of the shell, and heads, and the 
combined cross sectional area of all the tubes. 

219. What should be the location of the water gauge 
glass, relative to the water level in the boiler? 

Ans. It should be located at such a height as to bring 
the lower end of the glass tube on a level with the danger 
point for low water in the boiler. 

220. Where should the lower gauge cock be located 
relative to the danger point? 

Ans. About three inches above. 

222. Should an engineer or water tender depend entirely 
upon the water gauge glasses ? 

Ans. He should not, but should frequently open and try 
the gauge cocks. 

223. What should be done with the entire water column 
several times a day? 



276 Steam Engineering 

Ans. It should be blown out thoroughly. 

224. What should be done with the safety valves in 
order to make them reliable ? 

Ans. They should be allowed to blow off at least twice a 
week. 

225. Why is this necessary? 

Ans, Because the valves are liable to become corroded, 
and stick to their seats if not attended to properly. 

226. What is the rule for finding the bursting pressure 
of boilers? 

Ans. Multiply the tensile strength by the thickness and 
divide by one-half the diameter of the shell. 

227. How may the safe working pressure of a boiler be 
ascertained ? 

Ans. By dividing the bursting pressure by five. 

228. What is the rule for ascertaining the velocity of 
flow in a pump? 

Ans. Multiply the number of strokes per minute by 
length of stroke in feet. This will give piston speed. 

229. How may velocity of flow in the discharge pipe of 
a pump be found ? 

Ans. Divide square of diameter of water piston by the 
square of the diameter of pipe, and multiply by piston speed 
per minute. 

230. What is the rule for finding velocity in feet per 
minute required to discharge a given quantity of water in 
a given time? 

Ans. Multiply number of cubic feet to be discharged by 
144 and divide by area of pipe in inches. 

231. When the volume and. velocity of water to be dis- 
charged are known, how may the area of the pipe be ascer- 
tained ? 



Questions and Ansivers 277 

Ans. Multiply volume in cubic feet by 144 and divide 
by velocity in feet per minute. 

232. What is one of the main requisites in the success- 
ful burning of coal in a boiler furnace? 

Ans, A good draft. 

233. What is a common cause of lost economy in the 
operation of boilers? 

Ans. Air leaks in the brick settings. 

234. Mention another source of loss in connection with 
mechanical stokers. 

Ans. The dead area of grate that is covered with a thin 
layer of clinker, and ash. 

235. What is meant by the expression ^'^priming ?'^ 
Ans. Carrying over into the cylinder of water in the 

form of fine spray mingled with the steam. 

236. How may this be prevented to a large extent? 
Ans. By placing a baffle plate in the steam space of the 

boiler, directly under the dome. Steam separators may 
also be employed for this purpose. 

237. What should be the principal object in view in 
burning coal under a boiler? 

Ans. To transfer as many as possible of the total heat 
units in the coal, to the water in the boiler. 



278 



Steam Engineering 



Table 17 

propertie;s of saturated steam. 



t 






Tota 


Heat 




V 


S 


^ 




l-H 




above 


32° F. 




e 


st 


r§«; 




Absolute 

Pressure 

Lbs. per Sq. 


C (U 

J- 

Eh bO 

Q 








> 

> 


O o 

^3 


fe « 


il 

*> CO 

c 




1 ^ 


n 

■sis 

^ o 


l-H 








hH 






tH 


29.74 


.089 


32. 


0. 


1091.7 


1091.7 


208.080 


3333.3 


.0003 


29.67 


.122 


40. 


.8. 


1094.1 


1086.1 


154,330 


2472.2 


.0004 


29.56 


.176 


50. 


18. 


1097.2 


1079.2 


107,630 


1724.1 


.0006 


29.40 


.254 


60. 


28.01 


110(J.2 


1072.2 


76,370 


1223.4 


.0008 


29.19 


.359 


70. 


38.02 


1103.3 


1065.3 


54,660 


875.61 


.0011 


28.90 


.502 


80. 


48.04 


1106.3 


1058.3 


39,690 


635.80 


.0016 


28.51 


.692 


90. 


58.06 


1109.4 


1051.3 


29,290 


469.20 


.0021 


28.00 


.943 


100. 


68.08 


1112.4 


1044.4 


21,830 


349.70 


.0028 


27.88 


1. 


102.1 


70.09 


1113.1 


1043.0 


20,623 


334.23 


.0030 


25.85 


2. 


126.3 


94.44 


1120.5 


1026.0 


10,730 


173.23 


.0058 


•23.83 


3. 


141.6 


109.9 


1125.1 


1015.3 


7,325 


118.00 


.0085 


21.78 


4. 


153.1 


121.4 


1128.6 


1007.2 


5,588 


89.80 


.0111 


19.74 


5. 


162.3 


130.7 


1131.4 


1000.7 


4,530 


72:50 


.0137 


17.70 


6. 


170.1 


138.6 


1133.8 


995.2 


3,816 


61.10 


.0163 


15.67 


7. 


176.9 


145.4 


1135.9 


990.5 


3,302 


53.00 


.0189 


13.63 


8. 


i82.9 


15L5 


1137.7 


986.2 


2,912 


46.60 


.0214 


11.60 


9. 


188.3 


156.9 


1139.4 


982.4 


2,607 


41.82 


.0239 


9.56 


10. 


193.2 


161.9 


1140.9 


979.0 


2,361 


37.80 


.0264 


7.52 


11. 


197.8 


166.5 


1142.3 


975.8 


2,159 


34.61 


.0289 


5.49 


12. 


202.0 


170.7 


1143.5 


972.8 


1,990 


31.90 


.0314 


3.45 


13. 


205.9 


174.7 


1144.7 


970.0 


1,846 


29.60 


.0338 


1.41 


14. 


209.6 


178.4 


1145.9 


967.4 


1,721 


27.50 


.0363 


0.00 


14.7 


212.0 


180.9 


1146.6 


963.7 


1,646 


26.36 


.0379 



Properties of Saturated Steam 
Table 1 7 — continued 



279 



|5 

CA . 






- Total Heat 




OJ 


S 







above 32° F. 




S 

'0 
> 




. 




s « 


a ,„ 






^5 






In the Stea 
H 
Heat-uniti 






r-l 


J3 s 


0.3 


15 


213.3 


181.9 


1146.9 


965.0 


1,614 


25.90 


.0387 


1.3 


16 


216.3 


185.3 


1147.9 


962.7 


1,519 


24.33 


.0411 


2.3 


17 


219.4 


188.4 


1148.9 


960.5 


1,434 


23.00 


.0435 


3.8 


18 


222.4 


191.4 


1149.8 


958.3 


1,359 


21.80 


.0459 


4.3 


19 


225.2 


194.3 


1150.6 


956.3 


1,292 


20.70 


.0483 


I 5.3 


20 


227.9 


197.0 


1151.5 


954.4 


1,231 


19.72 


.0507 


1 6.3 


21 


230.5 


199.7 


1152.2 


952.6 


1,176 


18.84 


.0531 


1 7.3 


22 


233.0 


202.2 


1153.0 


950.8 


1,126 


18.03 


.0555 


8.3 


23 


235.4 


204.7 


1153.7 


949.1 


1,080 


17.30 


.0578 


9.3 


24 1 


237.8 


207.0 


1154.5 


947.4 


1,038 


16.62 


.0602 


10.3 


25 


240.0 


209.3 


1155.1 


945.8 


998 


16.00 


.0625 


11.3 


26 


242.2 


211.5 


1155.8 


944.3 


962 


15.42 


.0649 


12.3 


27 


244.3 


213.7 


1156.4 


942.8 


929 


14.90 


.0672 


13.3 


28 


246.3 


215.7 


1157.1 


941.3 


898 


14.40 


.0696 


14.3 


29 


248.3 


217.8 


1157.7 


939.9 


869 


13.91 


.0719 


15.3 


30 


250.2 


219.7 


1158.3 


938.9 


841 


13.50 


.0742 


16.3 


31 


252.1 


221.6 


1158.8 


937.2 


816 


13.07 


.0765 


17.3 


32 


254.0 


223.5 


1159.4 


935.9 


792 


12.68 


.0788 


18.3 


33 


255.7 


225.3 


1159.9 


93i.6 


769 


12.32 


.0812 


19.3 


34 


257.5 


227.1 


1160.5 


933.4 


748 


12.00 


.0835 


20.3 


35 


259.2 


228.8 


1161.0 


932.2 


728 


11.66 


.0858 


21.3 


36 


260.8 


230.5 


1161.5 


931.0 


709 


11.36 


.0880 


22.3 


37 


262.5 


232.1 


1162.0 


929.8 


691 


11.07 


.0903 


23.3 


38 


264.0 


233.8 


1162.5 


928.7 


674 


10.80 


.0926 


24.3 


39 


265.6 


235.4 


1162.9 


927.6 


658 


10.53 


.0949 


25.3 


40 


267.1 


236.9 


1163.4 


926.5 


642 


10.28 


.0972 


26.3 


41 


268.6 


238.5 


1163.9 


925.4 


627 


10.05 


.0995 


27.3 


42 


270.1 


240.0 


1164.3 


924.4 


613 


9.83 


.1018 


28.3 


43 


271.5 


241.4 


1164.7 


923.3 


600 


9.61 


.1040 


) 29.3 


44 


272.9 


242.9 


1165.2 


922.3 


587 


9.41 


.1063 


i 30.3 


45 


274.3 


244.3 


1165.6 


921.3 


575 


9.21 


.1086 


9 1 31.3 


46 


275.7 


245.7 


1166.0 


920.4 


563 


9.02 


.1108 


4 32.3 


47 


277.0 


247.0 


1166.4 


919.4 


552 


8.84 


.1131 


9 . 33.3 


48 


278.3 


248.4 


1166.8 


918.5 


541 


8.67 


.1153 


[ 34.3 


49 


279.6 


249.7 


1167.2 


917.5 


531 


8.50 


.1176 


8 35.3 


50 


280.9- 


251.0 


1167.6 


916.6 


520 


8.34 


.1198 


3 36.3 


51 


282.1 


252.2 


1168.0 


915.7 


511 


8.19 


.1221 


'9 37.3 


52 


283.3 


253.5 


1168.4 


914.9 


502 


8.04 


.1243 


" 38.3 


53 


284.5 


254.7 


1168.7 


914.0 


492 


7.90 


.1266 


39.3 


54 


285.7 


256.0 


1169.1 


913.1 


484 


7.76 


.1288 


40.3 


55 


286.9 


257.2 


1169.4 


912.3 


4'i6 


7.63 


.isn 


41.3 


56 


288.1 


258.3 


1169.8 


911.5 


468 


7.50 


.1333 


42.3 


57 


289.1 


259.5 


1170.1 


910.6 


460 


7.38 


.1355 


43.3 


58 


290.3 


260.7 


1170.5 


909.8 


453 


7.26 


.1377 


44.3 


59 


291.4 


261.8 


1170.8 


909.0 


446 


7.14 


.1400 


45.3 


60 


292.5 


262.9 


1171.2 


908.2 


439 


7.03 


.1422 


46.3 


61 


293.6 


264.0 


1171.5 


907.5 


432 


6.92 


.1444 


47.3 


62 


294.7 


265.1 


1171.8 


906.7 


425 


6.82 


.1466 


48.3 


63 


295.7 


266.2 


1172.1 


905.9 


419 


6.72 


.1488 



280 



Steam Engineering 
Table 1 7 — continued 









Total Heat 




(U 


g 


o 


4> C 




above 32° F. 


^ 


S 


.c S 


§ . 


3 


Absolute 

Pressure 

s. per Sq. 


p ^ 

H bfl 

Q 








'o 
> 




^^ 


Si 


u 




.2J 


^3 


j2 




+: « 
c W 






1; 


^J 


^ o 








1—1 


t— 1 






r-{ 


49.3 


64 


296.8 


267.2 


1172.4 


905.2 


413 


6.62 


.1511 


50.3 


65 


297.8 


268.3 


1172.8 


904.5 


407 


.6.53 


.1533 


51.3 


66 


298.8 


269.3 


1173.1 


903.7 


401 


6.43 


.1555 


52.3 


67 


299.8 


270.4 


1173.4 


903.0 


395 


6.34 


.1577 


53.3 


68 


300.8 


271.4 


1173.7 


902.3 


390 


6.25 


.1599 


54.3 


69 


301.8 


272.4 


1174.0 


901.6 


384 


6.17 


.1621 


55.3 


70 


302.7 


273.4 


1174.3 


900.9 


379 


6.09 


.1643 


56.3 


71 


303.7 


274.4 


1174.6 


900.2 


374 


6.01 


.1665 


57.3 


72 


304.6 


275.3 


1174.8 


899.5 


369 


5.93 


.1687 


58.3 


73 


305.6 


276.3 


1175.1 


898.9 


365 


5.85 


.1709 


59.3 


74 


306.5 


277.2 


1175.4 * 


898.2 


360 


5.78 


.1731 


60.3 


75 


307.4 


278.2 


1175.7 


897.5 


356 


5.71 


.1753 


61.3 


76 


308.3 


279.1 


1176.0 


896.9 


351 


5.63 


.1775 


62.3 


77 


309.2 


280.0 


1176.2 


896.2 


347 


5.57 


.1797 


63.3 


78 


310.1 


280.9 


1176.5 


895.6 


343 


5.50 


.1819 


64.3 


79 


310.9 


281.8 


1176.8 


895.0 


339 


5.43 


.1840 


65.3 


80 


311.8 


282.7 


1177.0 


894.3 


334 


5.37 


.1862 


66.3 


81 


312.7 


283.6 


1177.3 


893.7 


331 


5.31 


.1884 


67.3 


82 


313.5 


284.5 


1177.6 


893.1 


327 


5.25 


.1906 


68.3 


83 


314.4 


285.3 


1177.8 


892.5 


323 


5.18 


.1928 


69.3 


84 


315.2 


286.2 


1178.1 


891.9 


320 


5.13 


.1950 


70.3 


85 


316.0 


287.0 


1178.3 


891.3 


316 


5.07 


.1971 


71.3 


86 


316.8 


287.9 


1178.6 


890.7 


813 


5.02 


.1993 


72.3 


87 


317.7 


288.7 


1178.8 


890.1 


309 


4.96 


.2015 


73.3 


88 


318.5 


289.5 


1179.1 


889.5 


306 


4.91 


.2036 


74.3 


89 


319.3 


290.4 


1179.3 


888.9 


303 


4.86 


.2058 


75.3 


90 


320.0 


291.2 


1179.6 


888.4 


299 


4.81 


.2080 


76.3 


91 


320.8 


292.0 


1179.8 


887.8 


296 


4.76 


.2102 


77.3 


92 


321.6 


292.8 


1180.0 


887.2 


293 


4.71 


.2123 


78.3 


93 


322.4 


293.6 


1180.3 


886.7 


290 


4.66 


.2145 


79.3 


94 


323.1 


294.4 


1180.5 


886.1 


287 


4.62 


.2166 


80.3 


95 


323.9 


295.1 


1180.7 


885.6 


285 


4.57 


.2188 


81.3 


96 


324.6 


295.9 


1181.0 


885.0 


282 


4.53 


.2210 


82.3 


97 


325.4 


296.7 


1181.2 


884.5 


279 


4.48 


t?'>31 


83.3 


98 


326.1 


297.4 


1181.4 


884.0 


276 


4.44 


.2253 


84.3 


99 


326.8 


298.2 


1181.6 


883.4 


274 


4.40 


.2274 


85.3 


100 


327.6 


298.9 


1181.8 


882.9 


271 


4.36 


.2296 


86.3 


101 


328.3 


299.7 


1182.1 


882.4 


268 


4.32 


.2317 


87.3 


102 


329.0 


300.4 


1182.3 


881.9 


266 


4.28 


.2339 


88.3 


103 


329.7 


301.1 


1182.5 


881.4 


264 


4.24 


.2360 


89.3 


104 


330.4 


301.9 


1182.7 


880.8 


261 


4.20 


.2382 


90.3 


105 


331.1 


302.6 


1182.9 


880.3 


259 


4.16 


.2403 


91.3 


106 


331.8 


303.3 


1183.1 


879.8 


257 


4.12 


.2425 


92.3 


107 


332.5 


304.0 


1183.4 


879.3 


254 


4.09 


.2446 


93.3 


108 


333.2 


304.7 


1183.6 


878.8 


252 


4.05 


.2467 


94.3 


109 


333.9 


305.4 


1183.8 


878.3 


250 


4.02 


.2489 


95.3 


110 


334.5 


306.1 


1184.0 


877.9 


248 


3.98 


.2510 


96.3 


111 


335.2 


306.8 


1184.2 


877.4 


246 


3.95 


.2531 


97.3 


112 


335.9 


307.5 


1184.4 


876.9 


244 


3.92 


.2553 



Properties of Saturated Steam 
Table 1 7 — continued. 



281 





d 




Total Heat 






B 


o 








above 32° F. 








o . 




<v o ^ 


P^' 








^ 


'Z^ 






.HhJ 




Absolu 

Pressu] 

Lbs. per S 


H be 

V 

Q 


1 1 


In the Steam 
H 
Heat-units 


Latent H 

H-h 
Heat-un: 


O 
> 

> 




5i 


98.3 


113 


336.5 


308.2 


1184.6 


876.4 


242 


3.88 


.2574 


99.3 


114 


337.2 


308.8 


1184.8 


875.9 


240 


3.85 


.2596 


100.3 


115 


337.8 


309.5 


1185.0 


875.5 


238 


3.82 


.2617 


101.3 


116 


338.5 


310.2 


1185.2 


875.0 


236 


3.79 


.2638 


102.3 


117 


339.1 


310.8 


1185.4 


874.5 


234 


3.76 


.2660 


103.3 


118 


339.7 


311.5 


1185.6 


874.1 


232 


3.73 


.2681 


104.3 


119 


340.4 


312.1 


1185.8 


873.6 


230 


3.70 


.2703 


105.3 


120 


341.0 


312.8 


1185.9 


873.2 


228 


3.67 


.2764 


106.3 


121 


341.6 


313.4 


1186.1 


872.7 


227 


3.64 


.2745 


107.3 


122 


342.2 


314.1 


1186.3 


872.3 


225 


3.62 


.2766 


108.3 


123 


342.9 


314.7 


1186.5 


871.8 


223 


3.59 


.2788 


109.3 


124 


343.5 


315.3 


1186.7 


871.4 


221 


3.56 


.2809 


110.3 


125 


344.1 


316.0 


1186.9 


870.9 


220 


3.53 


.2830 


111.3 


126 


344.7 


316.6 


1187.1 


870.5 


218 


3.51 


.2851 


112.3 


127 


345.3 


317.2 


1187.3 


870.0 


216 


3.48 


.2872 


113.3 


128 


345.9 


317.8 


1187.4 


869.6 


215 


3.46 


.2894 


114.3 


129 


346.5 


318.4 


1187.6 


869.2 


1>13 


3.43 


.2915 


115.3 


130 


347.1 


319.1 


1187.8 


868.7 


212 


3.41 


.2936 


116.3 


131 


347.6 


319.7 


1188.0 


868.3 


210 


3.38 


.2957 


117.3 


132 


348.2 


320.3. 


1188.2 


867.9 


209 


3.36 


.2978 


118.3 


133 


348.8 


320.8 


1188.3 


867.5 


207 


3.33 


.3000 


119.3 


134 


349.4 


321.5 


1188.5 


867.0 


206 


3.31 


.3021 


120.3 


135 


359.0 


322.1 


1188.7 


866.6 


204 


3.29 


.3042 


121.3 


136 


350.5 


322.6 


1188.9 


866.2 


203 


3.27 


.3063 


122.3 


137 


351.1 


323.2 


1189.0 


865.8 


201 


3.24 


.3084 


123.3 


138 


351.8 


323.8 


1189.2 


865.4 


200 


3.22 


.3105 


124.3 


139 


352.2 


324.4 


1189.4 


865.0 


199 


3.20 


.3126 


125.3 


140 


352.8 


325.0 


1189.5 


864.6 


197 


3.18 


.3147 


126.3 


141 


353.3 


325.5 


1189.7 


864.2 


196 


3.16 


.3169 


127.3 


142 


353.9 


326.1 


1189.9 


863.8 


. 195 


3.14 


.3190 


i28 3 


143 


354.4 


326.7 


1190.0 


863.4 


193 


3.11 


.3211 


129.3 


144 


355.0 


327.2 


1190.2 


863.0 


192 


3.09 


.3232 


130.3 


145 


355.5 


327.8 


1190.4 


862.6 


191 


3.07 


.3253 


131.3 


146 


356.0 


328.4 


1190.5 


862.2 


190 


3.05 


.3274 


133.3 


148 


357.1 


329.5 


1190.9 


861.4 


187 


3.02 


.3316 


135.3 


150 


358.2 


330.6 


1191.2 


860.6 


185 


2.98 


.3358 


140.3 


155 


360.7 


333.2 


1192.0 


858.7 


179 


2.89 


.3463 


145.3 


160 


363.3 


335.9 


1192.7 


856.9 


174 


2.80 


.3567 


150.3 


165 


365.7 


338.4 


1193.5 


855.1 


169 


2.72 


.3671 


155.3 


170 


368.2 


340.9 


1194.2 


853.3 


164 


2.65 


.3775 


160.3 


175 


370.5 


343.4 


1194.9 


851.6 


160 


2.58 


.3879 


165.3 


180 


372.8 


345.8 


1195.7 


849.9 


156 


2.51 


.3983 


170.3 


185 


375.1 


348.1 


1196.3 


848.2 


152 


2.45 


.4087 


175.3 


190 


377.3 


350.4 


1197.0 


846.6 


148 


2.39 


.4191 


180.3 


195 


379.5 


352.7 


1197.7 


845.0 


144 


2.33 


.4296 


185.3 


200 


381.6 


354.9 


1198.3 


843.4 


141 


2.27 


.4400 


190.3 


205 


383.7 


357.1 


1199.0 


841.9 


138 


?^??. 


.4503 




210 


385.7 


359.2 


1199.6 


840.4 


135 


2.17 


.4605 


tOO.3 


215 


387.7 


361.3 


1200.2 


838.9 


132 


2.12 


.4707 



282 



Steam Engineering 
Table 17 — continued 









Total Heat 






S 


4-» 

o 




HH 




above 


32° F. 




B 


cS 


£ to 


;s'-' 




fa 

CD 

Q 






rt tfl 


3' 




r.-^ 




Absolute 

Pressure 

Lbs. per Sq. 


1 1 






o 
> 




+J o 


205.3 


220 


389.7 


362.2 


1200.8 


838.6 


129 


2.06 


.4852 


245.3 


260 


404.4 


377.4 


1205.3 


827.9 


110 


1.76 


.5686 


285.3 


300 


417.4 


390.9 


1209.2 


818.3 


96 


1.53 


.6515 


485.3 


500 


467.4 


443.5 


1224.5 


781.0 


59 


.94 


1.062 


685.3 


700 


504.1 


482.4 


1235.7 


753.3 


42 


.68 


1.470 


985.3 


1000 


546.8 


528.3 


1248.7 


720.3 


30 


.48 


2.082 



Combustion 



Combustion, as the term is used in steam engineering, 
is the rapid chemical combination of oxygen with carbon, 
hydrogen^, and sulphur, with the accompaniment of heat 
and light. The substance which combines with the oxygen 
is the combustible. The combustion is perfect when the 
combustible is oxidized to the highest possible degree ; thus, 
conversion of carbon into carbon dioxide (COg) represents 
perfect combustion, while its conversion to monoxide (CO) 
is imperfect combustion, since the monoxide can be further 
burned and finally converted into COg. 

Kindling Point. As in many other chemical processes, 
a certain degree of heat is necessary to cause the union of 
the oxygen and combustible; the temperatures necessary 
to cause this union are the kindling temperatures, and are 
approximately as given in the following table by Stromeyer : 

Table 18 
kindling temperatures. 

Lignite Dust 300° F 

Sulphur 470 

Dried Peat 435 

Anthracite Dust 570 

Coal 600 

Cokes Red Heat 

Anthracite Red Heat 750 

Carbon Monoxide Red Heat 1211 

Hydrogen 1030 or 1200 

The Oxygen necessary for combustion is supplied from 
the air. Its density is 1.10521 (x\ir=l) ; its weight 
0.088843 pounds per cubic foot at 32° F., and atmospheric 
pressure; its atomic weight is 16; a pound of air contains 

283 



284 



Steam Engineering 



0.2315 pounds of oxygen^ and 1 pound of oxygen is con- 
tained in 4.32 pounds of air. 

Carbon (C)^ the most abundant combustible^, has atomic 
weight of 12^ and reaches the boiler furnace as a constituent 
of oil^ gas^ coal^ charcoal^ wood^ etc. 

Hydrogen (H) occurs free in small quantity in some 
fuels^ but is usually in combination with the carbon. Its 
atomic weight is 1; its density is 0.0692 (Air=l) ; and its 
weight per cubic foot at 32° F. and atmospheric pressure 
is 0.00559 pounds. The heating value of 1 pound of pure 
carbon is rated at 14^500 heat units^, while 1 pound of hydro- 
gen gas contains 62^000 heat units. 

Coal, Analysis of coal shows that it contains moisture, 
fixed carbon, volatile matter, ash and sulphur in various 
proportions according to the quality of the coal. Table 19 
deduced from a few of the many valuable tables of analysis 
of the coals of the United States will show the composition 
of the principal bituminous coals in use in this country for 

Table 19 
composition of various coals. 



State 


Kind of Coal 


Mois- 
ture 


Vola- 
tile 
Matter 


Fixed 
Carbon 


Ash 


Sul- 
..hur 


Pennsylvania 


Youghiogheny 


1.03 


36.49 


59.05 


2.61 


0.81 


Pennsylvania 


Connellsville 


1.26 


30.10 


59.61 


8.23 


0.'<8 


West Virginia 


Quinimont 


0.76 


18.65 


79.26 


1.11 


0.23 


West Virginia 


Fire Creek 


0.61 


22.34 


75.02 


1.47 


0.56 


E, Kentucky 


Peach Orchard 


4.60 


35.70 


53.28 


6.42 


1.08 


E. Kentucky 


Pike County 


1.80 


26.80 


67.60 


3.80 


0.97 


Alabama 


Cahaba 


1.66 


33.28 


63.04 


2.02 


0.53 


Alabama 


Pratt Co.'s 


1.47 


32.29 


59.50 


6.73 


1.22 


Ohio 


Hocking Valley 


6.59 


35.77 


49.64 


8.00 


1.59 


Ohio 


Muskingum Valley 


3.47 


37.88 


53.30 


5.35 


2.24 


Indiana 


Block 


8.50 


31.00 


57.50 


3.00 




Indiana 


Block 


2.50 


44.75 


51.25 


1.50 




W. Kentucky 


Nolin River 


4.70 


33.24 


54.94 


11.70 


2.54 


W. Kentucky 


Ohio County 


3.70 


30.70 


45.00 


3.16 


1.24 


Illinois 


Big Muddy 


6.40 


30.60 


54.60 


8.30 


1.50 


Illinois 


Wilmington 


15.50 


32.80 


39.90 


11.80 




Illinois 


'' screenings 


14.00 


28.00 


34.20 


23.80 




Illinois 


Duquoin 


8.90 


23.50 


60.60 


7.00 





Combustion 285 

steam purposes. Two samples are selected from each of 
the great coal producing states^ with the exception of 
Illinois^ from which four were taken. 

The process of combustion of fuel consists in the union 
of the carbon and hydrogen of the fuel with the oxygen of 
the air. Each atom of carbon combines with two atoms of 
oxygen^ and the energetic vibration set up by their com- 
bination is heat. Bituminous coal contains a large per- 
centage of volatile matter which is released and flashes into 
flame when the coal is thrown into the furnace^, and unless 
air is supplied in large amounts at this stage of the com- 
bustion there will be an excess of smoke^ and consequent 
loss of carbon. On the other hand there is a loss in ad- 
mitting too much air because the surplus is heated to the 
temperature of the furnace without aiding the combustion, 
and will carry off to the chimney just as many heat units 
as were required to raise it from the temperature at which 
it entered the furnace, to that at which it enters the uptake. 
It will therefore be seen that a great advantage will be 
gained by first allowing the air that is needed above the 
fire to pass over or through heated bridge walls, or side 
walls. Some kinds of coal need more air for their com- 
bustion than do others, and good judgment and close ob- 
servation are needed on the part of the fireman to properly 
regulate the supply. 

Sulphur (S, atomic weight 32) is found in most eoals' 
and in some oils. It is usually present in a combined form, 
either as sulphide of iron, or sulphate of lime ; in the latter 
form it has no heating value. Its presence in fuel is ob- 
jectionable, because the gases formed from its combustion 
attack the metal of the boiler and cause rapid corrosion,, 
particularly in presence of moisture. 



286 Steam Engineering 

Nitrogen (N) is drawn into the furnace with the air. 
Its atomic weight is 14; its density is 0.9701 (Air=^l) ; 
its weight per cnbic foot at 32° F. and atmospheric pres- 
sure is .07831 pounds; each pound of air at atmospheric 
pressure contains 0.7685 pounds of nitrogen^ and 1 pound 
of nitrogen is contained in 1.301 pounds of air. 

Nitrogen performs no useful office in combustion, and 
passes through the furnace without change. It dilutes the 
air^ absorbs heat and reduces the temperature of the prod- 
ucts of combustion^ and is the chief source of heat loss in 
furnaces. 

Combining Weights, When chemical elements unite to 
form a new compound they do so in definite proportions 
which are always the same, and the union produces heat, 
the quantity of which is also invariable. Thus, a pound of 
carbon, when carbon dioxide is formed, will always unite 
with 2 2-3 pounds of oxygen, and give off 14,600 B. T. U. 
As an intermediate step the carbon might unite with 1 1-3 
times its weight of oxygen, and produce 4,450 B. T. U., but 
in its further conversion to CO2 it would unite with an 
additional 11-3 times its weight of oxygen and evolve the 
other 10,150 B. T. IT., since the heat developed in any 
chemical combination depends upon the initial, and final 
states, and not upon any intermediate change. 

Carlorific Value of Fuel, The amount of heat liberated 
per pound of fuel undergoing perfect combustion is called 
the calorific value of the fuel. 

Some boilers will make steam more economically by 
partly closing the ash-pit doors, while others require the 
same doors to be kept wide open. The quantity of air re- 
quired for the combustion of one pound of coal is, by 
volume, about 150 cubic feet; by weight, about 12 pounds. |* 



Combustion 287 

The temperature of the furnace is usually about 2,500°, 
in some cases reaching as high as 3,000°. The temperature 
of the escaping gases should not be much above nor below 
400° F. for bituminous coal. The waste heat in the escap- 
ing gases can be utilized to great advantage by passing 
them through what are called economizers before they es- 
cape into the chimney. These economizers consist of coils, 
or stacks of cast iron pipe placed within the flue or breeching 
leading from the boilers to the chimney and are enveloped 
in the hot gases, while the feed water is passed through 
the pipes on its way to the boilers, the result being that 
considerable heat is thus imparted to the feed water that 
would otherwise go to waste. 

In order to attain the highest economy in the burning 
of coal in boiler furnaces two factors are indispensable, 
viz., a constant high furnace temperature, and quick com- 
bustion, and these factors can only be secured by supplying 
the fresh coal constantly just as fast as it is burned, and 
also by preventing as much as possible the admission of 
cold air to the furnace. This is why the automatic or 
mechanical stoker, if it be of the proper design, is more 
economical and causes less smoke than hand firing. The 
fireman when he puts in a fire is prone to shovel in a good 
supply all at once, and this has the tendency to greatly 
reduce the temperature of the furnace, while at the same 
time it retards combustion. On the other hand the me- 
chanical stoker supplies the coal continuously only as fast 
as it is required and no faster, and the furnace doors to 
lot need to be opened at all, by which a large volume of 
cold air is prevented from entering the furnace and reduc- 
ing the temperature. The author does not wish to be under- 
stood as recommending the adoption and use of mechanical 



288 Steam Engineering 

stokers to replace hand firings but he draws this contrast 
between the two methods of firing in order that it may be 
of some benefit to the thousands of honest toilers who earn 
a livelihood by shoveling coal into boiler furnaces. 

The problem of the economical use of coal and the abate- 
ment of the smoke nuisance^ especially in our large cities, 
h^as of late years become so serious that it is to the interest 
of every engineer, and especially every fireman, to use the 
utmost diligence, care and good judgment in the use of 
■coal, and to emulate as much as possible the methods of the 
mechanical stoker. 

Heat. All matter, whether solid, liquid or gaseous, con- 
sists of molecules, or atoms, which are in a state of continual 
vibration, and the result of this vibration is heat. The 
intensity of the heat evolved depends upon the degree of 
;agitation to which the molecules are subject. 

Heat Effects, When heat is added to or taken from a 
body, either the temperature of the body is altered, or its 
volume is varied, or its state is changed. Thus, if heat be 
added to water under atmospheric pressure, the temperature 
of the water increases until it reaches 212° F. If more 
heat be added and the pressure remains unchanged, the 
temperature does not further increase, but the water evapor^ 
ates into steam. Heat thus changes water from a liquid to 
a gaseous state. If heat be abstracted from water the tem- 
perature is reduced until it reaches 32° F., after which any 
diminution of heat does not further decrease the tempera- 
ture, until the liquor is converted into a solid, or ice. The 
quantity of heat passing from one body to another can thus 
be estimated by the effects produced. Therefore heat is 
something that can be both transferred and measured. 

The general effect of heat on a body is to increase its 



Heat 289 

volume. If heat be abstracted from a body the contrary 
effect ensueS;, and the volume is diminished. Hence the 
general principle^ to which, however, there are some ex- 
ceptions, that heat expands and cold contracts. These 
effects, prising from a change of temperature, are produced 
in very different degrees according to the nature of the 
bodies. They are small ' in solids, greater in liquids, and 
greater still in gases. 

It is well known that the work expended in friction 
apparently is lost as regards mechanical work; that heat 
is developed when friction occurs; that the greater the 
friction the greater is the amount of heat produced. Ex- 
periments have proved that the amount of heat generated 
by friction is exactly equivalent to the amount of work 
lost, whence it is shown that heat, like mechanical work 
is one of the forms of energy. 

Thermometers. In consequence of the uniform expan- 
sion of mercury and its great sensitiveness to heat, it is the 
fluid most commonly used in the construction of thermome- 
ters. In all thermometers the freezing and the boiling 
point of water, under mean atmospheric pressure at sea 
level, are assumed as two fixed points, but the division of 
the scale between these two points varies in different coun- 
tries, hence there are in use three thermometers, known as 
the Fahrenheit, the Centrigrade or Celsius, and the Eeau.- 
mur. In the Fahrenheit, the space between the two fixed 
points is divided into 180 parts ; the boiling point is marked 
212, and the freezing point is marked 32, and zero is a 
temperature which, at the time this thermometer was in- 
vented, was incorrectly imagined to be the lowest tempera- 
ture attainable. In the Centrigrade and the Reaumur 
scales the distance between the two fixed points is divided 



290 



Steam Engineering 



COMPARISON 


Table 20 
of thermometer scales. 




Fahrenheit 


Centigrade 


Reaumur 


Absolute Zero 


—460.66 

10 
20 
30 
32 

39.1 

50 

75 
100 
200 
212 
250 
300 
350 


—273.70 

—17.77 

—12.23 

—6.67 

—1.11 

0. 

3.94 

10. 

23.89 

37.78 

93.34 

100. 

121.11 

148.89 

176.67 


— 218.96 


Freezing Point 


• —14.22 

—9.77 

—5.33 

—0.88 

0. 


Maximum Density of 

Water 


3.15 


Boiling Point 


8. 

19.11 
30.22 
74.66 
80. 




96.88 
119.11 
141.33 



P=9-5 C+32^=9-4 E+32° 
C=5-9(F— 32°')=5-4E. 
E=4:-5C=4-9(F— 32°). 

into 100 and 80 parts, respectively. In each of these two 
scales the freezing point is marked 0, and the boiling point 
is marked 100 in the Centigrade, and 80 in the Eeaumnr. 
Each of the 180, 100, or 80 divisions is termed a degree. 
Table 20 and the appended formulas are useful for con- 
verting one scale to another. 

1 

Absolute zero. At 32° P. a perfect gas expands • 

492.66 
part of its volume, if its temperature is increased one de- 
gree and its pressure remains constant. This rate of ex- 
pansion holds good at all temperatures above the freezing 
point, in the case of the gas, which would double its volume 
if under a constant pressure its temperature were raised to 
320+492.66=524.66° R, while under a diminution of 
temperature it would shrink and finally disappear at a 
temperature of 492.66—32=460.66° below zero F. 



Heat 291 

Therefore the temperature 460.66°^ or for the sake of 
simplicity, 461° P. is taken as absolute zero. 

Until as late as the beginning of the nineteenth century 
two rival theories in regard to the nature of heat had been 
advocated by scientists. The older of these theories was that 
heat was a material substance, a subtle, elastic fluid termed 
caloric, and that this fluid penetrated matter something 
like water penetrates a sponge. But this theory was shown 
to be false by the wonderful researches and experiments of 
Count Eumford at Munich, Bavaria, in 1798. 

By means of the friction between two heavy metallic 
bodies placed in a wooden trough filled w4th water, one of 
the pieces of metal being rotated by machinery driven by 
horses. Count Eumford succeeded in raising the tempera- 
ture of the water in two and one-half hours from its original 
temperature of 60° to 212° F., the boiling point, thus 
demonstrating that heat is not a material substance, but 
that it is due to vibration or motion, an internal commotion 
among the molecules of matter. This theory, known as 
the Kinetic theory of heat, has since been generally ac- 
cepted, although it was nearly fifty years after Eumford 
advocated it in a paper read before the Eoyal Society of 
Great Britain in 1798, before scientists generally became 
converted to this idea of the nature of heat, and the science 
of thermo-dynamics was placed on a firm basis. 

During the period from 1840 to 1849 Dr. Joule made a 
■series of experiments which not only confirmed the truth 
of Count Eumford^s theory that heat was not a material 
substance, but a form of energy which may be applied to or 
taken away from bodies, but Joule's experiments also es- 
tablished a method of estimating in mechanical units or foot 
pounds the amount of that energy. This latter was a most 



292 Steam Engineering 

important discovery^ because by means of it the exact rela- 
tion between heat and work can be accurately measured. 

The first law of thermo-dynamics is this: Heat and 
mechanical energy^ or work are mutually convertible. That 
is, a certain amount of work will produce a certain amount 
of heat, and the heat thus produced is capable of producing 
by its disappearance a fixed amoimt of mechanical energy 
if rightly applied. The mechanical energy in the form of 
heat which, through the medium of the steam engine, has 
revolutionized the world, was first stored up by the sun^s 
heat millions of years ago in the coal which in turn, by 
combustion, is made to release it for purposes of mechanical 
work. 

The general principles of Dr. Joule^s device' for meas- 
uring the amount of work in heat are illustrated in Fig. 
^ 102. It consists of a small copper cylinder containing a 
known quantity of water at a known temperature. Inside 
the cylinder and extending through the top was a vertical 
shaft to which were fixed paddles for stirring the water. 
Stationary vanes were also placed inside the cylinder. Mo- 
tion was imparted to the shaft through the medium of a 
cord or small rope coiled around a drum near the top of 
the shaft and running over a grooved pulley or sheave. To 
the free end of the cord a known weight was attached. 
This weight was allowed to fall through a certain distance, 
and in falling it turned the shaft with its paddles, which in 
turn agitated the water, thus producing a certain amount 
of heat. To illustrate, suppose the weight to be 77.8 pounds, 
and that by means of the crank at the top end of the shaft 
it has been raised to the zero mark at the top of the scale. 
(See Fig. 102.) One pound of water at 39.1° F. is poured 
into the copper cylinder, which is then closed and the weight 



Heat 



293 



released. At the moment the weight passes the 10 foot 
mark on the scale^ the thermometer attached to the cylinder 
will indicate that the temperature of the water has been 
raised one degree. Then multiplying the number of pounds 
in the weight by the distance in feet through which it fell 





y^'tal^tjiflit 



e^ Ctank 
? ^ fiaddies 



Fig. 102 



J 

J 
¥ 

-i 
- 1 



Thus, 



will give the number of foot pounds of work done. 
77.8 poundsXlO feet=778 foot pounds. 

The heat unit or British thermal unit (B. T. U.) is the 
quantity of heat required to raise the temperature of one 
I pound of water one degree^ or from 39° to 40° F., and 



294 Steam Engineering 

the amount of mechanical work required to produce a 
unit of heat is 778 foot pounds. Therefore the mechanical 
equivalent of heat is the energy required to raise 778 pounds 
one foot high^ or 77.8 pounds 10 feet high^ or 1 pound 778 
feet high. Or again^ suppose a one-pound weight falls 
through a space of 778 feet or a weight of 778 pounds falls 
one foot^ enough mechanical energy would thus be de- 
veloped to raise a pound of water one degree in tempera- 
ture, provided all the energy so developed could be utilized 
in churning or stirring the water, as in Joule^s machine. 
Hence the mechanical equivalent of heat is 778 foot pounds. 

Specific Heat. The specific heat of any substance is 
the ratio of the quantity of heat required to raise a given 
weight of that substance one degree in temperature, to the 
quantity of heat required to raise an equal weight of water 
one degree in temperature when the water is at its maxi- 
mum density, 39.1° F. To illustrate, take the specific heat 
of lead, for instance, which is .031, while the specific heat 
of water is 1. That means that it would require 31 times 
as much heat to raise one pound of water one degree in 
temperature as it would to raise the temperature of a pound 
of lead one degree. 

The following table gives the specific heat of diflEerent 
substances in which engineers are most generally interested : 



Heat 295 

Table 21 
specific heat of various substances. 

Water at 39.1'' F 1.000 

Ice at 32° F 504 

Steam at 212° F 480 

Mercury 033 

Cast iron 130 

Wrought iron .113 

Soft steel .116 

Copper 095 

Lead 031 

Coal 240 

Air 238 

Hydrogen 3.404 

Oxygen 218 

Nitrogen 244 

Sensible Heat and Latent Heat, The plainest and most 
simple definition of these two terms is that given by Sir 
Wm. Thomson. He says: ^^Heat given to a body and 
warming it is sensible heat. Heat given to a body and not 
warming it is latent heat.^^ Sensible heat in a substance 
is the heat that can be measured in degrees of a thermome- 
ter^ while latent heat is the heat in any substance that is 
not shown by the thermometer. 

To illustrate this more fully a brief reference to some 
experiments made by Professor Black in 1762 will no doubt 
make the matter plain. It will be remembered that at that 
early date comparatively little was known of the true 
nature of heat^ hence Professor BlacFs investigations and 
discoveries along this line appear all the more wonderful. 
He procured equal weights of ice at 32^ F. and water at the 
same temperature, that is, just at the freezing point, and 
placing them in separate glass vessels suspended the vessels 
in a room in which the uniform temperature was 47° F. 
He noticed that in one-half hour the water had increased 
7° F. in temperature, but that twenty half hours elapsed 
before all of the ice was melted. Therefore he reasoned that 
twenty times more heat had entered the ice th^n had entered 



296 Steam Engineering 

the water^ because at the end of twenty half hours when 
the ice was all melted the water in both vessels was of the 
same temperature. The water having absorbed 7° of heat 
during the first half hour must have continued to absorb 
heat at the same rate during the whole of the twenty half 
hours^ although the thermometer did not indicate it. From 
this he calculated that 7°X^0=140° of heat had become 
latent or hidden in the water. 

In another experiinent Professor Black placed a lump 
of melting ice^ which he estimated to be at a temperature 
of 33^ F. on the surface, in a vessel containing the same 
weight of water at 176° F., and he observed that when the 
whole of the ice had been melted the temperature of the 
water was 33° F., thus proving that 143° of heat (176°— 
33°) had been absorbed in melting the ice and was at that 
moment latent in the water. By these two experiments 
Professor Black established the theory of the latent heat of 
water, and his estimate was very near the truth because 
the results obtained since that time by the greatest experi- 
menters show that the latent heat of water is 142 heat units, 
or B. T. U. 

BlacFs experiment for ascertaining the latent heat in 
steam at atmospheric pressure was made in the following 
simple manner : He placed a flat, open tin dish on a hot 
plate over a fire and into the dish he put a small quantity 
of water at 50° F. In four minutes the water began to 
boil, and in twenty minutes more it had all evaporated. 
In the first four minutes the temperature had increased 
212° — 50° = 162°, and the temperature remained at 
212° throughout the twenty minutes that it required to 
evaporate all the water, despite the fact that the water 
had been receiving heat during this period at the same rate 



Heat 297 

as during the first four minutes. He therefore reasoned 
that in the twenty minutes the water had absorbed five 
times as much heat as it had in the four minutes^ or 160° X 
5=810°, without any sensible rise in temperature. There- 
fore the 810° became latent in the steam. Owing to the 
crude nature of the experiment Professor Black's estimate 
of the number of degrees of latent heat in steam was in- 
correct, as it has been proven by many famous experimenters 
since then that the latent heat of steam at atmospheric 
pressure is 965.7 B. T. U. 

It will thus be perceived that what is meant by the term 
latent heat is that quantity of heat which becomes hidden, 
or latent when the state of a body is changed from a solid 
to a liquid, as in the case of melting ice, or from a liquid 
to a gaseous state, as with water evaporated into steam.. 
But the heat so disappearing has not been lost, on the 
contrary it has, while becoming latent, been doing an im- 
mense amount of work, as can easily be ascertained by 
means of a few simple figures. It has been seen that a 
heat unit is the quantity of heat required to raise one 
pound of water one degree in temperature and also that the 
mechanical equivalent of heat, or, in other words, the 
mechanical energy stored in one heat unit is equal to 778 
foot pounds of work. 

A horse power equals 33,000 foot pounds of energy in 
one minute of time, and a heat unit=778^33,000=.0236, 
or about 1-43 of a horse-power. The work done by the 
heat which becomes latent in converting one pound of ice 
at 32° P. into water at the same temperature=142 heat 
unitsX778 foot pounds=110,476 foot pounds, which di- 
vided by 33,000 equals 3.34 horse-power. Again, by the 
evaporation of one pound of water from 32° F. into steam 



298 Steam Engineering 

at atmospheric pressure^ 965.7 units of heat become latent 
in the steam and the work done:i=965.7X'^'^8=751,314 
foot pounds=22.7 horse-power. It will thus be seen what 
tremendous energy lies stored in one pound of coal, which 
contains from 12,000 to 14,500 heat units, provided all 
the heat could be utilized in an engine. 

Total Heat of Evaporation. In order to raise the tem- 
perature of one pound of water from the freezing point, 
32° P., to the boiling point, 212° P., there must be added 
to the temperature of the water 212°— 32° = 180°. This 
represents the sensible heat. Then to make the water boil 
at atmospheric pressure, or, in other words, to evaporate it, 
there must still be added 965.7 B. T. U., thus 180+965.7= 
1,145.7, or in round numbers 1,146 heat units. This repre- 
sents what is termed the total heat of evaporation at at- 
mospheric pressure and is the sum of the sensible and latent 
heat in steam at that pressure. But if a thermometer were 
held in steam evaporating into the open air, as, for instance, 
in front of the spout of a tea-kettle, it would indicate but 
212° P. . 

When steam is generated at a higher pressure than 212°, 
the sensible heat increases and the latent heat decreases 
slowly, while at the same time the total heat of evaporation 
slowly increases as the pressure increases, but not in the 
same ratio. As, for instance, the total heat in steam at 
atmospheric pressure is 1,146 B. T. U., while the total heat 
in steam at 100 pounds gauge pressure is 1,185 B. T. U., 
and the sensible temperature of steam at atmospheric pres- 
sure is 212°, while at 100 pounds gauge pressure the tem- 
perature is 338 and the latent heat is 876 B. T. U. 



Water 299 



WATER. 



Water, The elements that enter into the composition of 
pure water are the two gases, hydrogen and oxygen, in the 
following proportions: 

Hydrogen Oxygen 

By volume 2 1 

By weight 11.1 88.9 

Perfectly pure water is not attainable, neither is it de- 
sirable nor necessary to the welfare of the human race, 
because the presence of certain proportions of air and 
ammonia add greatly to its value as an agent for manu- 
facturing purposes and for generating steam. The nearest 
approach to pure water is rain water, but even this contains 
2.5 volumes of air to each 100 volumes of water. Pure 
distilled water, such for instance as the return water from 
steam heating systems, is not desirable for use alone in a 
boiler, as it will cause corrosion and pitting of the sheets, 
but if it is mixed with other wat?r before going into the 
boiler its use is highly beneficial, as it will prevent to a 
certain degree the formation of scale and incrustation. 
Nearly all water used for the generation of steam in boilers 
contains more or less scale-forming matter, such as the 
carbonates of lime and magnesia, the sulphates of lime and 
magnesia, oxide of iron, silica and organic matter, which 
latter tends to cause foaming in boilers. 

The carbonates of lime and magnesia are the chief causes 
of incrustation. The sulphate of lime forms a hard crystal- 
line scale which is extremely difficult to remove when once 
formed on the sheets and tubes of boilers. Of late years 
the intelligent application of chemistry to the analyzing of 



300 Steam Engineering 

feed waters has been of great benefit to engineers and steam 
nsers^ in that it has enabled them to properly treat the 
water with solvents either before it is pnmped into the 
boiler^ or by the introduction into the boiler of certain scale 
preventing compounds made especially for treating the 
particular kind of water used. Where it is necessary to 
treat water in this manner great care and watchfulness 
should be exercised by the engineer in the selection and 
use of a boiler compound. 

Prom ten to forty grains of mineral matter per gallon 
are held in solution by the waters of the different rivers, 
streams and lakes ; well and mine water contain still more. 

Water contracts and becomes denser in cooling until it 
reaches a temperature of 39.1° P.^ its point of greatest 
density. Below this temperature it expands and at 3.2° F. 
it becomes solid or freezes^ and in the act of freezing it ex- 
pands considerably^ as every engineer who has had to deal 
with frozen water pipes can testify. 

Water is 815 times heavier than atmospheric air. The 
weight of a cubic foot of water at 39.1° is approximately 
62.5 pounds, although authorities differ on this matter, 
some of them placing it at 62.379 pounds, and others at 
62.425 pounds per cubic foot. As its temperature increases 
its weight per cubic foot decreases until at 212° P. one cubic 
foot weighs 59.76 pounds. 

The table which follows is compiled from various sources 
and gives the weight of a cubic foot of water at different 
temperatures. 



Water 

Table 22 
weight of cu. ft. of water 



301 



Temper- 


Weight per 


Temper- 


Weight per. 


Temper- 


Weight per 


ature 


Cubic Foot 


ature 


Cubic Foot 


ature 


Cubic Foot 


32° F. 


()4.42 lbs. 1 


132° F. 


61.52 lbs. II 230° F. 


59.37 lbs. 


42« 


62.42 |i 142" 


1 61.34. 


, 240° 


59.10 


52° 


62.40 1 


1 152° 


61.14 


i 250° 


58.85 


62° 


62.36 1 


1 162° 


60.94 


1 260° 


58.52 


72° 


62.30 |i 172° 


60.73 


1 270° 


58.21 


82'» 


62.21 1 


1 182° 


1 60.50 


1 300° 


57.26 


92° 


62.11 1 


1 192° 


60.27 


1 330° 


56.24 


102° 


62.00 1 


1 202° 


60.02 


1 360° 


55.16 


112° 


61.86 |i 212° 


59.'<6 


1 390° 


54.03 


122° 


61.70 1 


1 220° 


59.64 


1 420° 


52.86 



The boiling point of water varies according to the pres- 
sure to which it is subject. In the open air at sea level 
the boiling point is 212° F. When confined in a boiler 
under steam pressure the boiling point of water depends 
upon the pressure and temperature of the steam^ as^ for 
instance^, at 100 pounds gauge pressure the temperature of 
the steam is 338° P.^ to which temperature the water must 
be raised before its molecules will separate and be converted 
into steam. In the absence of any pressure^ as in a perfect 
vacuum^ water boils at 32° F. temperature. In a vacuum 
of 28 inches^ corresponding to an absolute pressure of .943 
pounds^ water will boil at 100°^ and in^a vacuum of 26 
inches^ at which the absolute pressure is 2 pounds^ the boil- 
ing point of water is 127° F. On the tops of high moun- 
tains in a rarefied atmosphere^ water will boil at a much 
lower temperature than at sea level, for instance at an alti- 
tude of 15,000 feet above sea level water boils at 184° F. 

Table 23 gives the boiling point of water at various alti- 
tudes above sea level, also the atmospheric pressure in 
pounds per square inch. 



302 



Steam Engineering 



Table 23 
boiling point of water at various altitudes. 



Boiling Point 
in degrees 


Altitude above 
Sea Level. 


Atmospheric 
Pressure. 


Barometer, 


Fahrenheit. 


Feet. 


Pounds per 
square inch. 


Inches. 


184 


15,221 


8.19 


16.79 


185 


14,649 


8.37 


17.16 


186 


14,075 


8.56 • 


17.54 


187 


13,498 


8.75 


17.93 


188 


12,934 


8.94 


18.32 


189 


12,367 


9.13 


18.72 


190 


11,799 


9.33 


19.13 


191 


11,243 


9.53 


19.54 


192 


10,685 


9.74 


19.96 


193 


10,127 


9.95 


20.39 


194 


9,579 


10.16 


20.82 


195 


9,031 


10.38 


21.26 


196 


8,481 


10.60 


2L71 


197 


7,932 


10.82 


22.17 


198 


7,381 


11.05 


22.64 


199 


6,843 


11.28 


23.11 


200 


6,304 


11.52 


23.59 


201 


5,764 


11.76 


24.08 


202 


5,225 


12.01 


24.58 


203 


4,697 


12.25 


25.08 


204 


4,169 


12.51 


25.59 


205 


3,642 


12.77 


26.11 


206 


3,115 


13.03 


26.64 


207 


2,589 


13.29 


27.18 


208 


2,063 


13.57 


27.73 


209 


1,539 


13.84 


28.29 


210 


1,025 


14.12 


28.85 


211 


512 


14.41 


29.42 


212 


Sea-Level 


14.70 


30.00 



STEAM. 

Steam. Having discussed to some extent the physical 
properties of water^ it is now in order to devote some time 
to the study of the nature of steam^ which is simply water 
in its gaseous form, made so by the application of heat. 

As has been stated in another portion of this book, mat- 
ter consists of molecules or atoms inconceivably small in 
size, yet each having an individuality, and in the case of 
solids or liquids, each having a mutual cohesion or attrac- 
tion for the other, and all being in a state of continual vi- 
bration, more or less violent according to the temperature 
of the body. 




steam 303 

The law of gravitation which holds the universe together, 
also exerts its wonderful influence on these atoms, and 
causes them to hold together with more or less tenacity 
according to the nature of the substance. Thus it is much 
more difficult to chip off pieces of iron or granite than it 
is of wood. But in the case of water and other liquids the 
atoms, while they adhere to each other to a certain extent, 
still they are not so hard to separate, in fact, they are to 
some extent repulsive to each other, and unless confined 
within certain bounds the atoms will gradually scatter and 
spread out, and finally either be evaporated or sink out of 
sight in the earth^s surface. Heat applied to any substance 
tends to accelerate the vibrations of the molecules, and if 
enough heat is applied it will reduce the hardest sub- 
stances to a liquid or gaseous state. 

The process of the generation of steam from water is 
simply an increase of the natural vibrations of the mole- 
cules of the water, caused by the application of heat until 
they lose all attraction for each other and become instead 
entirely repulsive, and unless confined will fly off into 
space. But being confined they continually strike against 
the sides of the containing vessel, thus causing the pressure 
which steam or any other gas exerts when under confine- 
ment. 

Of course steam, like other gases, when under pressure, 
is invisible, but the laws governing its action are well 
known. These laws, especially those relating to the expan- 
sion of steam, will be more fully discussed in the section 
on the Indicator. The temperature of steam in contact 
with the water from which it is generated, as for instance 
in the ordinary steam boiler, depends upon the pressure 
under which it is generated. Thus at atmospheric pres- 



304 Steam Engineering 

sure its temperature is 212^ F. If the vessel is closed and 
the pressure increased the temperature of the steam and 
also that of the water rises. 

Saturated Steam. When steam is taken directly from 
the boiler to the engine without being superheated, it is 
termed saturated steam. This does not necessarily imply 
that it is wet and mixed with spray and moisture. 

Superheated Steam. When steaiii is conducted into or 
through a vessel or coils of pipe separate from the boiler 
in which it was generated^ and is there heated to a higher 
temperature than that due to its pressure, it is said to be 
superheated. 

Dry Steam. When steam contains no moisture it is said 
to be dry. Dry steam may be either saturated or super- 
heated. 

Wet Steam. When steam contains mist or spray inter- 
mingled it is termed wet steam, although it may have the 
same temperature as dry saturated steam of the same pres- 
sure. 

During the further consideration of steam in this book^, 
saturated steam will be mainly under discussion, for 
the reason that this is the normal condition of steam as 
used most generally in steam engines. 

Total Heat of Steam. The total heat in steam includes 
the heat required to raise the temperature of the water 
from 32° F. to t^e temperature of the steam plus the heat 
required to evaporate the water at that temperature. This 
latter heat becomes latent in the steam, and is therefore 
called the latent heat of steam. 

The work done by the heat acting within the mass of 
water and causing the molecules to rise to the surface is 
termed by scientists internal work, and the work done in 



steam 305 

compressing the steam already formed in the boiler, or in 
pushing it against the superincumbent atmosphere, if the 
vessel be open, is termed external work. There are, there- 
fore, in reality three elements to be taken into consideration 
in estimating the total heat of steam, but as the heat ex- 
pended in doing external work is done within the mass it- 
self it may, for practical purposes, be included in the 
general term latent heat of steam. 

Density of Steam. The expression density of steam 
means the actual weight in pounds, or fractions of a pound 
avoirdupois of a given volume of steam. This is a very 
important point for young engineers especially to remem- 
ber, so as not to get the two terms, pounds pressure and 
pounds weight, mixed, as some are prone to do. 

Volume of Steam, By this term is meant the volume 
as expressed by the number of cubic feet in one pound 
weight of steam. 

Relative Volume of Steam. This expression has refer- 
ence to the number of volumes of steam produced from 
one volume of water. Thus the steam produced by the 
evaporation of one cubic foot of water from 39° F. into 
steam at atmospheric pressure will occupy a space of 1646 
cubic feet, but, as the steam is compressed and the pres- 
sure allowed to rise, the relative volume of the steam be- 
comes smaller, as for instance at 100 pounds gauge pres- 
sure the steam produced from one cubic foot of water will 
occupy but 237.6 cubic feet, and if the same steam was com- 
pressed to 1,000 pounds absolute or 985.3 pounds gauge 
pressure it would then occupy only 30 cubic feet. 

The condition of steam as regards its dryness may be 
approximately estimated by observing its appearance as it 
issues from a pet cock or other small opening into the 



306 Steam Engineering 

atmosphere. Dry/ or nearly dry steam containing about 
1 per cent of moisture will be transparent close to the 
orifice through which it issues, and even if it is of a gray- 
ish white color it may be estimated to contain not over 2 
per cent of moisture. 

Stea;in in its relation to the engine should be considered 
in the character of a vehicle for transferring the energy, 
created by the heat, from the boiler to the engine. For 
this reason all steam drums, headers and pipes should be 
thoroughly insulated in order to prevent, as much as pos- 
sible, the loss of heat or energy by radiation. 

There is a wide difference in the value of different sub- 
stances for protection from radiation, their value varying 
nearly in the inverse ratio of their conducting power for 
heat, up to their ability to transmit as much heat as the 
surface of the pipe will radiate, after which they become 
detrimental, rather than useful, as covering. This point 
is reached nearly at baked clay or brick. 

Table 24 shows the relative value of various non-con- 
ductors of heat, and table 25 gives the loss of heat from 
steam pipes protected, and unprotected. 

Where two values are given in table 24 for the same 
substance the lower one is for the denser condition. 

A smooth or polished surface is of itself a good protec- 
tion, polished tin or Eussia iron having a ratio, for radia- 
tion, of 53 to 100 for cast iron. Mere color makes but lit- 
tle difference. 

Hair or wool felt, and most of the better non-conduc- 
tors, have the disadvantage of becoming soon charred from 
the heat of steam at high pressure, and sometimes of tak- 
ing fire therefrom. 

^^Mineral wool,^^ a fibrous material made from blast fur- 
nace slag, is the best non-combustible covering, but is quite 



steam 307 

brittle, and liable to fall to powder where much jarring 
exists. 

Air space alone is one of the poorest of non-conductors, 
though the best owe their efficiency to the numerous mi- 
nute air cells in their structure. This is best seen in the 
value of different forms of carbon, from cork charcoal to 
anthracite dust, the former being three times as valuable 
for this purpose, though in chemical constitution they are 
practically identical. 

Any suitable substance used to prevent the escape of 
steam heat should not be less than one inch thick. 

Table 24 
relative value of non-conducting materials. 

Substance Value 

♦Loose V^ool 3.35 

*Loose Lampblack 1.12 

*Geese Feathers 1.08 

*Felt, Hair or Wool 1. 

*Carded Cotton 1. 

♦Charcoal from Cork .87 

Mineral Wool 68 to .83 

Fossil Meal 66 to .79 

* Straw Rope, wound spirally .77 

♦Rice Chaff, loose .76 

Carbonate Magnesia 67 to .76 

♦Charcoal from Wood 63 to .75 

♦Paper 50 to .74 

*Cork .71 

♦Sawdust 61 to .68 

Past<" of Fossil Meal anH Hair (^3 

Wood Ashes .61 

* Wood, across grain 40 to .55 

Loam, dry and open .55 

Chalk, ground, Spanish white .51 

Coal Ashes 35 to .49 

Gas-house Carbon .47 

Asbestos Paper .47 

Paste of Fossil Meal and Asbestos .47 

Asbestos, fibrous .36 

Plaster of Paris, dry .34 

Clay, with vegetable fiber .34 

Anthracite Coal, powdered .29 

Coke in lumps .27 

Air Space, undivided 14 to .22 

Sand .17 

Baked Clay, Brick .07 

Glass .05 

Stone m 

* Combustible, and sometimes dangerous. 



308 Steam Engineering 

The following table gives the :oss of heat from steam 
pipes^ naked and clothed with wool or hair felt^ of dif- 
ferent thickness^ the steam pressure being assumed at 75 
pounds and the external air at 60°. 



steam 



309 



.^^c 



JD 00 CO Ol p CO 
00 4^ 00 ^^o 



oo-^050coax 

CO COM ^MtO 



MMCO 
3tOrf^->l MOO CO 

3Q0 4i^CO^PP 
rfi. *M ^ CO isD CO QO 



rf».M-^>^ roM 

looorfi'Cn qpoooo 



-^ to lO O to • M 



OOMMCO! o 



COOOCTCOM* 



jfi- P UT 00 Ci 
CO b to CO 05 • 



OOMMCO. 

rfi^cbo-iO' 

-J coco 05M' 



CO -^ i4i^ tO,M • 

-q to ►1^ CJ! a< • ,. 
to4^cocoM' a 



MCO. 
h<^05C000O' 

urpoooiM: ;^ 
to CO b CO ^ • "rfi. 



Thickness of Covering 
in inches 



Loss in Units 

per foot run 

per hour 



Ratio of Loss 



Feet in Length 
per H. P. lost 



Loss in Units 

per foot run 

per hour 



Ratio of Loss 



Feet in Length 
per H. P. lost 



Loss in Units 

per foot run 

per hour 



Ratio of Loss 



Feet in Length 
per H. P. lost 



Loss in Units 

per foot run 

per hour 



Ratio of Loss 



Feet in Length 
per H. P. lost 



-qOxCOMM* 
CO OT rfi' -v| M • 
CJXC0OC0 4i.' 



Loss in Units 

per foot run 

per hour 



Ratio of Loss 



Feet in Length 
per H. P. lost 



o 

in 

> 












310 Steam Engineering 

Flow of Steam Through Pipes. The approximate 
weight of any fluid which will flow in one minute through 
any given pipe with a given head or pressure may be found 
by the following formula: 



in which W=rweight in pounds avoirdupois, (i=diameter 
in inches, Z)=^density or weight per cubic foot, pi=the 
initial pressure, p2=pr6ssure at end of pipe, and L= 
the length in feet. Table 26 gives, approximately, the 
weight of steam per minute which will flow from various 
initial pressures, with one pound loss of pressure through 
straight smooth pipes, each having a length of 240 times 
its own diameter. 

For sizes of pipe below 6-inch, the flow is calculated 
from the actual areas of ^'^standard^^ pipe of such nominal 
diametera 

For horsepower, multiply the figures in the table by 2. 
For any other loss of pressure, multiply by the square root 
of the given loss. For any other length of pipe, divide 
2JfO by the given length expressed in diameters, and mul- 
tiply the figures in the table by the square root of this 
quotient, which will give the flow for 1 lb. loss of pres- 
sure. Conversely, dividing the given length by 240 will 
give the loss of pressure for the flow given in the table. 

The loss of head due to getting up the velocity, to the 
friction of the steam entering the pipe, and passing elbows 
and valves, will reduce the flow given in the tables. The 
resistance at the opening, and that at a globe valve, are 
each about the same as that for a length of pipe equal to 



steam 



311 



CD v*^ Ks 00 M '--1 00 bs 00 CO io I-' ito 

■ ■COCriOOOOMCOrf^-^-^-^Ol-^ 



OllOO«D00^05CiXi^WtOM 
OOOOOOOOOOOOM 



W W }s3 to to JN5 to to to M M M M 

wQQO'-ibihfi'CoI-'obobscoM 
-^3ih4^MC005to-aMtotoooto 



a>picnt^*^ji^4i^wcowtotojo 

M bt to o ^ c^ to CO bi CO CD or b 



05C;x^|i.C0C0t0l-iOpCD000i01 



bo^^cDcoCTOiC^cooobooto 

COMMI-*05CfXCO-^a^OiCDOlOi 



4xcD00CDCOCO«qv*i.COCD>-iCDM 



COCOtOtOtOtOtOtOI-'Ml-il-iM 
COOOOOSOT^^COOCDOOOiCOM 
pTpltOCDOOUXJ-i p5p[-iM^M 
tOMCDCDbsJ^COCOCDQobiCDOS 



050XC;nOX^^4s-4!^rfi'COCOCOtOtO 



-ClCOOOCJTCOOSCOCDUlOSOitOM 



OCDOOOO-^-lOJOSOSOIh^O^CO 

OMOti-'-acocDoiOi^ooMCo 

CDpOtO[-ipOppMtO^Oip^a5 

biCDtobrcDcocDcncobo^coco 



Hfi-COtOl-'MOOCDOOOO-lOSrf^ 
00C?tC;?tCDrfi'00tOOl00QMMCD 

^cocn^i^popcD^ppsMpT 

tobiCobOh^CDbl^tOCDCDQOCO 



tOtOtOMM)-*MI-i|-iMM 

COMQCDOO^OiCI^'tOMCD-^ 
^05OMC04i>.|^C0MCDrf»>--lCD 
CDO500O5OitOtOC;«CDM-lCDtO 



COCOtOtOtOtOtOtOtOMMMM 

*«>MCD000:CJX4».t0OQ005ai'M 

do^4i.ooooxo^^•-^oo-^coc^ 

C0OOat-lOh*^0000CDCDC0C 



Initial 


Pressure by] 


Gauge. Pounds 


per Square Inch. 




:^ 






M 


u 






M 


1— 1 




;^ 


> 


M 








W 


?- 


to 


^ 








o 




O 








►5j 


in 


to 




(T» 

3 


;r 






^3 








CO 


t— ( 


B 




i^ 


p 






c 




^ 


n> 




o 




^ 


ffi 


3 




w 


'O 




C/2 


o 






c 






3 


ai 


t-< 


03 




w 






^ 


^ 




o 


o 


Oi 




3 




O 


►o 




^ 


o 






c 




w 





00 


> 


o 




II 




M 
O 








o 


Cfl 




t— 1 






> 


•-t 




g 




to 


H 






C/) 




M 






c;x 




M 




00 








to 



312 Steam Engineering 

114 diameters divided by a number represented by 1-f- 
(3. 6 -^diameter). For the sizes of pipes given in the table^ 
these corresponding lengths are : 

I 1 li 2 2i 8 4 5 6 8 10 12 15 18 
20 25 34 41 47 52 60 66 71 79 84 88 92 95 

The resistance at an elbow is equal to 2/3 that of a 
globe valve. These equivalents — for openings for elbows^ 
and for valves — must be added in each instance to the ac- 
tual length of pipe. Thus a 4 in. pipe^ 120 diameter 
(40 feet) longy with a globe valve and three elbows^ would 
be equivalent to 120+60+60+ (3X4*0) =360 diameters 
long; and 360-^-240=:ly2. It would therefore have 11/2 
pounds loss of pressure at the flow given in the table, or 
deliver (l-4-Vl-!/2=-816) 81.6 per cent of the steam 
with the same (1 pound) loss of pressure. 

Flow of Steam From a Given Orifice, Steam of any 
pressure flowing through an opening into any other pres- 
sure, less than three-fifths of the initial, has practically a 
constant velocity, 888 feet per second, or a little over ten 
miles per minute; hence the amount discharged in pounds 
is proportionate to the weight or density of the steam. To 
ascertain the pounds, avoirdupois, discharged per minute^ 
multiply the area of opening in inches, by 370 times the 
IV eight per cubic foot of the steam. (See Table 17.) 

Or the quantity discharged per minute may be approx- 
imately found by Eankine^s formula : 

W=6 a p-^7 
in which TF= weight in pounds, 6^=: area in square inches, 
and p=absolute pressure. The theoretical flow requires 
to. be multiplied by fc=0.93, for a short pipe, or 0.63 for 
a thin opening, as in a plate, or a safety valve. 



steam SI? 

Where the steam flows into a pressure more than 2/3 
the pressure in the boiler : 



W=1.9 a lc-\/{p—S)S 
in which 8= difference in pressure between the two sides^ 
in pounds per square inch^ and a, p, and k as above. 

To reduce to horsepower^ multiply by 2. 

Where a given horsepower is required to flow through 
a given openings to determine the necessary difference in 
pressure : 



^~ 2 ~N 4 "Ua'k 

QUESTIONS AND ANSWERS. 

238. What is meant by the term combustion as used in 
steam engineering? 

Ans. It is the rapid chemical combination of oxygen 
with the carbon^ hydrogen and sulphur in the fuel with 
the accompaniment of heat and light. 

239. What is meant by the symbol CO2? 

Ans, CO2 represents perfect combustion^ viz.^ the cre- 
ation of carbon dioxide. 

240. What is the most abundant combustible in nature ? 
Ans. Carbon. 

241. How many heat units are contained in one pound 
3f pure carbon? 

Ans, 14,500. 

242. What is the heating value of one pound of hydro- 
gen gas? 

Ans, 62,000. 

243. Give the composition of coal. 



314 Steam Engineering 

Ans. Fixed carbon^ volatile matter, ash and sulphur in 
various proportions, depending upon the quality of the 
coal. 

244. Is sulphur desirable as a constituent of coal ? 
Ans, It is not. The gases formed from its combustion 

attack the metal of the boiler, causing corrosion. 

245. What office does nitrogen perform in combustion? 
Ans, No useful office. Eather it is a detriment, and 

in fact is the chief source of loss in furnaces. It is drawn 
in with the air. 

246. What is meant by the term calorific value of fuel? 
Ans, The amount of heat liberated per pound of fuel 

undergoing perfect combustion. 

248. What are economizers in connection with a boiler 
plant ? 

Ans, Coils or stacks of cast iron pipe placed within the 
smoke flue, or breeching and surrounded by the hot gases 
while the water is passed through the pipes on its way to 
the boilers, thus receiving an additional amount of heat. 

249. What two factors are necessary in order to attain 
economy in the burning of coal? 

Ans, A constant high furnace temperature and quick 
combustion. 

250. Define the term heat. 

Ans, Heat is the result of the vibration of the mole- 
cules or atoms composing matter. 

251. Upon what does the intensity of heat depend? 
Ans. Upon the rapidity of the agitation to which the 

molecules are subject. 

252. What are the general effects of heat? 

Ans, When heat is added to, or taken away from a 
body the temperature of the body is altered and its volume 
is varied. 



steam 315 

253. What is absolute zero? 

Ans. It is that degree of temperature at which, owing 
to the intense cold, a perfect gas would disappear. Abso- 
lute zero is 461° below the zero of the Fahrenheit ther- 
mometer. 

254. What is a heat unit (B. T. U.) ? 

Ans, It is the quantity of heat required to raise the tem- 
perature of one pound of water one degree, or from 39° 
to 40° F. 

25^, What is the mechanical equivalent of heat? 

Ans, 778 foot pounds; in other words, 778 pounds 
raised one foot high. 

256. What is the specific heat of any substance? 

Ans, The ratio of the quantity of heat required to raise 
a given weight of that substance one degree in tempera- 
ture, to the quantity of heat required to raise an equal 
weight of water one degree when the water is at its maxi- 
mum density, viz., 39.1° F. 
• 257. What is latent heat? 

Ans. Heat given to a body and not warming it. 

258. What is sensible heat? 

Ans, Heat given to a body and warming it. 

259. Of what is pure water composed? 

Ans. By volume — Hydrogen 2 parts, oxygen 1. 

By weight — Hydrogen 11.1 parts, oxygen 88.9. 

260. Is perfectly pure water desirable for use in a steam 
boiler ? 

Ans, It is not, as it will cause corrosion and pitting of 
the sheets. 

261. What two ingredients in water are the chief causes 
of incrustation in boilers ? 

Ans, The carbonates of lime and magnesia. 



316 Steam Engineering 

262. What is steam? 

Ans. Steam is the vapor of water generated by an in- 
crease of the natural vibrations of molecules of the water 
through the application of heat. 

263. What is saturated steam? 

Ans, Steam taken directly from the boiler to the enginei 
without being superheated. | 

264. What is superheated steam? 

Ans. Steam that has been heated to a higher tempera- 
ture than that due to its pressure. 

265. What should be done with all pipes through which 
live steam is conducted for purposes of heating, or power? 

Ans, They should be well protected by a covering, in 
order to prevent loss of heat by radiation. 

266. In what respect should steam be considered in its 
relation to the engine? 

Ans. As a vehicle for transferring the heat energy from 
the boiler to the engine. 



Evaporation Tests 



Evaporation Tests, The object of making evaporation 
tests of steam boilers is primarily to ascertain how many 
pounds of water the boilers are evaporating per pound of 
coal burned; but these tests can and should be made to 
determine several other important points with reference 
to the operation of the boilers^ as for instance: 1. The 
efficiency of the boiler and furnace as an apparatus for the 
consumption of fuel and the evaporation of water ; whether 
this apparatus is performing its guaranteed duty in this 
respect^ and how it compares with a known standard. 2. 
, To determine the relative economy of different varieties of 
coal^ also to determine the relative value of fuels other than 
coal^ such as oil^ gas^ etc. 3. To ascertain whether or not 
the boilers as they are operated under ordinary every day 
conditions are being run as economically as they should be. 
4. In case the boilers^ owing to an increased demand for 
steam^ fail to supply a sufficient quantity without forcing 
the fires^ whether or not additional boilers are needed^ or 
whether the trouble could be overcome by«a change of con- 
ditions in operating them. 

Tests for the last three purposes named can be made by 
the regular engineering force of the plant^ but in case a 
controversy should arise between the maker of the boiler 
and the purchaser regarding the first mentioned pointy viz., 
the guaranteed efficiency of the boiler or the furnace, the 
services of experts in boiler testing may be resorted to. 

Preparing for a Test. All testing apparatus should be 
kept in such shape that it will not take three or four days 

317 



318 Steam Engineering 

io get it ready for making a test. On the contrary, it can 
be and should be always kept in condition ready for use. 
so that the preparations for making a test will occupy but 
a short time. A small platform scale sufficiently large for 
weighing a wheel-barrow load of coal should also be pro- 
vided in addition to the apparatus heretofore described. 

The capacity of each of the two tanks illustrated in Fig. 
^^y can be determined in two ways, either by measuring 
ihe cubical contents of each or by placing them one at a 
iime on the scales, filling them with water to within a few 
inches of the top, and note the weight. Also make a per- 
manent mark on the inside at the water level. The water 
should then be permitted to run out until within an inch 
or so of the outlet pipe near the bottom, where another 
plain mark should be made, after which the empty tank 
should be again weighed, then by subtracting the last 
i\^eight from the first the exact number of pounds of water 
that the tank will contain between the top and bottom 
marks can be determined and a note made of it. 

It is much more convenient to have each tank contain 
the same quantity of water, although not absolutely neces- 
sary. The tanks should also be numbered 1 and 2 re- 
spectively in order to prevent confusion in keeping a record 
of the number of tanks full of water used during the test. 
Care should be exercised to have the water with which the 
tanks are filled while on the scale, at or near the same tem- 
perature as that at which it is to be fed into the boiler dur- 
ing the test. Otherwise there is liability of error owing 
to the variation in the weight of water at different tem- 
peratures. In order to guard against this, the capacity in 
cubic feet of each tank between the top and bottom marks 
should be ascertained by measuring the distance between 
the marks, also the diameter, or, if the tanks be square, the 



Evaporation Tests 319 

length of one side^ after which the cubical contents can be 
easily figured and noted down. By knowing the capacity 
in cubic feet of each tank all possibility of error in the 
weight of feed water will be eliminated. 

The scales for weighing the coal can be fitted with a 
temporary wooden platform large enough to accommodate 
a wheel-barrow^ and after it has been balanced with the 
empty barrow on it^ the record of weight of coal burned 
during the test can be easily kept. 

The same barrow should be used throughout the test^ 
and to save complications in estimating the weighty the 
same number of pounds of coal should be filled in the 
barrow each load. The coal passer will learn in a short 
time to fill the barrow to within a few pounds of the same 
weight each load by counting the shovelsful and the dif- 
ference can easily be adjusted by having a small box of 
coal near the scale from which to take a few lumps to bal- 
ance the load^ or if there is too much coal in the barrow 
some of it can be thrown into the box. 

At least two separate tally sheets should be provided, 
marked respectively coal and water^ and the one for coal 
placed near the scale, and care should be taken that each 
load is tallied as soon as it is weighed. The tally sheet for 
water should be near the measuring tanks and as soon as 
a tank is emptied it should be tallied. The temperature 
of the feed water should be taken at least every thirty 
minutes, or oftener if possible, from a thermometer placed 
in the feed pipe near the check valve. The readings should 
be noted and, at the expiration of the test, the average 
taken. 

To Find the Cubic Contents of a Barrel. To find the 
cubic contents of a barrel, square the largest diameter, then 
multiply by 2, then add the square of the head diameter; 



320 Steam Engineering 

multiply this sum by the length of the cask and that prod- 
uct by 0,2618. For example^ a barrel whose largest di- 
ameter is 21 inches^ head diameter 18 inches and height 
33 inches: 21X21X^=882; 18X18=324; 324+882= 
1206; 1206X33=39,798; 39,798X0.2618=10,419.11 cubic 
inches. Dividing by 231 for gallons gives 45.10 gallons. 

If the object of the test is to ascertain the efficiency of 
the boiler and furnace it is absolutely necessary that the 
boiler and all its appurtenances be put in good condition, 
by cleaning the heating surface both inside the boiler and 
outside, scraping and blowing the soot out of the tubes, if 
it be a return tubular boiler, and blowing the soot and ashes 
from between the tubes if it is a water tube boiler. All 
dust, soot and ashes should be removed from the outside 
of the shell and also from the combustion chamber and 
smoke connections. The grate bars and sides of the fur- 
nace should be cleared of all clinker, and all air leaks made 
as close as possible. The boiler and all its water connec- 
tions should be free from leaks, especially the blow-off 
valve or cock. If any doubt exists as to the latter it should 
be plugged or a blind flange put on it. It is very essential 
that there should be no way for the water to leak out of 
the boiler, neither should any water be allowed to get 
into the boiler during the test except that which is 
measured by passing through the tanks. 

In making an efficiency test it is essential that the boiler 
should be run at its fullest capacity from the beginning to 
the end of the test. Therefore arrangements should be 
made to dispose of the steam as fast as it is generated. If 
the boiler is in a battery connected with a common header, 
its mates can be fired lighter during the test, but if there 
is but the one boiler in use a waste steam pipe should be 



Evaporation Tests 321 

temporarily connected through which the surplus steam^ if 
there is any^ can be discharged into the open air through 
a valve regulated as required. Before starting the test the 
boiler should be thoroughly heated by having been run 
several hours at the ordinary rate. The fire should then be 
cleaned and put in good condition to receive fresh coal. 

At the time of beginning the test the water level should 
be at or near the height ordinarily carried^ and its position 
marked by tying a cord around one of the guard rods of 
the gauge glass^ and^ to prevent all possibility of error^ the 
height of the water in the glass should be measured and a 
note made of it. Note also the time that the first lot of 
weighed coal is fed to the furnace^ and record it as the 
starting time. The steam pressure should be noted at the 
beginning of the test^ and at regular intervals during the 
progress of the test in order that the average pressure may be 
obtained. 

At the close of the test all of the above conditions should 
be as nearly as possible the same as at the beginning; the 
quantity;^ and condition of the fire should be the same^ also 
the steam pressure and water level. This can be ac- 
complished only by careful work towards the close of the 
test. 

During the progress of the test care should be exercised 
to prevent any waste of coal^ especially in cleaning the fire. 
The ash made during the test must not be wet down until 
after it is weighed^ as in all calculations for combustible 
and non-combustible matter in the coal the ash should be 
dry. 

The duration of the test should be at least ten hours if 
it is possible to continue it for that length of time. The 
feed pump should be kept running at such speed as will 



322 Steam Engineering 

suppl}^ the water to the boiler as fast as it is evaporated, 
and no faster. If at the close of the test a portion of water 
is left in the last tank tallied it can be measured^ and de- 
ducted from the total. And if any weighed coal is left 
on the floor it should be weighed back and deducted from 
the total weight. If the boiler is fed by an injector in- 
stead of a pump during the test, the injector should receive 
steam directly from the boiler under test through a well 
protected pipe. Also, the temperature of the feed water 
should be taken from the measuring tanks, or at least from 
the suction side of the injector, for the reason that the 
water in passing through the injector receives a large quan- 
tity of heat imparted to it by live steam directly from the 
boiler. Therefore the temperature of the water after it 
leaves the injector would not be a true factor for figuring 
the evaporation. 

Determination of the Percentage of Moisture in the 
Steam, This is an important point in estimating the re- 
sults of an evaporation test for the reason that each pound 
weight of moisture in the steam as it leaves the boiler rep- 
resents a pound of water that has not been evaporated into 
steam, and should therefore be deducted from the total 
weight of water fed into the boiler during the test. 

The steam should be tested for moisture by taking 
samples of it from the steam pipe or header as near the 
boiler as possible in order to guard against additional 
moisture caused by condensation. 

Practically all saturated steam contains water, varying 
in amount from a fraction of one per cent when the steam 
is generated in a properly designed boiler fed with good 
water, to five per cent or even more when the feed water is 
bad, or the boilers are of defective design. Not only is the 



Evaporation Tests 323 

heat absorbed by raising this water from the boiler feed 
temperature to the steam temperature practically wasted, 
but the water causes further loss by increasing the initial 
condensation in the engine cylinder ; it also interferes with 
proper cylinder lubrication, causes knocking in the engine, 
and water hammer in the steam pipe. 

Quality of Steam. The percentage weight of steam, in 
a mixture of steam and water, is called the quality of the 
steam. Thus steam of quality 99.5 contains one-half of 
one per cent by weight of moisture. 

Calorimeters. The apparatus used to determine the 
moisture in steam is called a calorimeter, though the name 
is inapt, since the instrument is in no sense a measurer of 
heat. The first form used was the ^^barrel calorimeter.^^ 
In this apparatus liability of error is so great that its use 
is practically abandoned. Modern calorimeters are usually 
of either the throttling or separator type. 

Throttling Calorimeter. Figure 103 shows a section 
through a typical form of the instrument. Steam is drawn 
from the vertical pipe by a nipple arranged as later de- 
scribed, passes around the first thermometer cup as shown, 
then through a hole about %-inch diameter in the disk as 
shown. It next passes around the lower thermometer cup, 
after which it is permitted to escape. Thermometers are 
inserted into the cups, which are then filled with cylinder 
oil, and when the whole apparatus is heated the tempera- 
ture of the steam before, and after passing through the 
bole in the disk is noted. 

The instrument and pipes leading to it should be thor- 
oughly covered to diminish the radiation loss. 

When steam passes from a higher to a lower pressure, 
as in this case, no work has to be done in overcoming a re- 



324 



Steam Engineering 



sistance; hence assuming there is no loss from radiation, 
the quantity of heat is exactly the same after passing the 
disk as it was ahead of it. Suppose that the higher, steam 
pressure is 150 pounds by gauge, and the lower pressure 
that of the atmosphere. The total heat in a pound of dry 
steam at the former pressure is 1193.5 B. T. U. and at the 
latter pressure is 1146.6 B. T. U., difference, 46.9. B. T. U. 




TQ ATMOSPHERE 

Fig. 103 
throttling calorimeter and sampling pipe 

As this heat still exists in the steam of lower pressure, its 
effect is to superheat that steam. Assuming the specific 
heat of steam to be 0.48, the steam will then be superheated 

46.9 

=97.7 degrees. Suppose, however, the steam had 

0.48 

contained one per cent, of moisture. Before any super- 
heating could occur, this moisture would have to be evap- 
orated into steam of atmospheric pressure. Since the latent 
heat of steam at atmospheric pressure is 965.8 B. T. U. 



Evaporation Tests • 325 

it follows that the one per cent, of moisture would require 

9.658 B. T. U. to evaporate it, leaving only 46.9—9.658= 

37.242 B. T. IT. available for superheating, hence the super- 

37.242 

heat would be =77.6° as against 97.7 degrees in the 

0.48 

preceding case. In a similar manner the degree of super- 
heat for other amounts of moisture can be determined, 
and the action of the throttling calorimeter is based on 
this fact as will now be shown. 

Let £r=total heat of steam at boiler pressure. 
i=latent heat of steam at boiler pressure. 
A=:total heat of steam at reduced pressure after 

passing the disk. 
#1= temperature of saturated steam at the reduced 

pressure. 
^2= temperature of steam after expanding through 
opening in the disk. 
0.48=specific heat of saturated steam. 
iT^proportion of moisture in the steam. 
The difference between the B. T. U.'s in a pound of steam 
at boiler pressure and after passing the disk is the heat 
which must evaporate the moisture in the steam, and then 
do the superheating, hence. 

H—]i=xL—OAS (t^—t^), therefore 
i7_7^_0.48 (t^—t^) 

x= [61 

L 
Almost invariably the lower pressure is taken as that 
of the atmosphere where /i=1146.6 and ^1^=212, hence 
the formula becomes 

H— 1146.6— 0.48 {t.—212) 

X=- [71 



326 Steo.m Engineering 

For practical work it is more convenient to dispense with 
the upper thermometer in the calorimeter, and substitute 
an accurate steam gauge whose readings are more easily 
noted. 

Sources of Error, There are two. The first is that the 
specific heat of superheated steam, while given as 0.48 is 
far from being certain, and only future investigation can 
determine the true value. The second source of error is 
loss of heat by radiation. Evidently from the moment the 
steam enters the sampling nipple it is losing heat, hence 
when it passes through the small opening and into the 
lower pressure the heat available for evaporating moisture, 
and superheating will be diminished by just the amount 
lost by radiation, hence the value of ^3 ^^ ^^ lower than 
it should be. This is sometimes corrected for as follows: 
A valve in the steam pipe beyond the calorimeter nipple 
is closed, and the steam left in a quiescent state for about 
ten minutes, and it is assumed that by doing this all the 
moisture in the steam will settle out, and that a sample of 
steam drawn from the pipe will be dry. Steam is then 
allowed to flow through the calorimeter and the tempera- 
ture of the lower thermometer is noted. Let T denote this 
temperature. Since the sample of steam was assumed to 
be dry it follows that if there were no loss from radiation 
the value of T would be that due to all of the liberated 
heat being absorbed in superheating the steam of lower 
temperature. There is, however, a loss of radiation, and 
the effect of this is to condense some of the steam of lower 
pressure, and the water thus formed must be evaporated 
before any superheating can be done. Let x^ represent the 
proportion of water thus formed, then evidently 
H—h—OA^ (T—t,) 



Evaporation Tests 327 

Now this amount of water was not in the steam orig- 
inally, but was caused by condensation in the instrument, 
hence the true amount of moisture in the steam, which 
may be denoted by X, will be 

H—h—OAS (t.—t^) 
X=:x — a;^= 



H—h—0A8 (T—t^) 

L 
0.48 {T—t,) 



vss 



L 

The disadvantages of this method are: [1) It assumes 
that during the test the boiler pressure will remain the 
same as it was when T was determined, which is seldom 
practicable; (2) It assumes that the sample of steam 
drawn into the instrument when determining T was ab- 
solutely dry, although experiment has shown that this as- 
sumption is not necessarily true. Notwithstanding these 
facts, formula [8] is much used by engineers because of 
its simplicity and convenience, and any error due to its 
use is of no practical significance. 

There are many forms of throttling calorimeter, all of 
which operate on precisely the same principle as the simple 
design shown in Pig. 103. An extremely convenient and 
compact design is shown in Fig. 104. It consists of two 
concentric cylinders screwed to a cap containing a ther- 
mometer cup. The steam pressure is measured by a gauge 
placed in the supply pipe, or any other convenient place. 
Steam passes through the opening A, expands to atmos- 
pheric pressure, and its temperature at this pressure is 
measured by a thermometer placed in the cup C. To pre- 
vent radiation losses the annular space between the two 



328 



Steam Engineering 



cylinders is used as a jacket^ and is supplied with steam 
through the hole B. 

The limits of the throttling calorimeter at sea level are 
from about four per cent of moisture at eighty pounds 
pressure to six per cent at 200 pounds pressure. If there 
is a greater content of moisture the liberated heat is in- 

~ D 




Fig. 104 
compact throttling calorimeter 



sufficient to evaporate it^ and superheat the steam thus 
generated. 

Separating Calorimeter, The separating calorimeter 
(Fig. 105) mechanically separates the entrained vrater 
from the steam and collects it in a reservoir, where its 
amount is either indicated by a gauge glass or deterinined 



Evaporation Tests 



329 



by draining if off and weighing it. The steam passes out 
of the calorimeter through an orifice of known size, so 



y ^sg^ I 




Fig. 105 
separating calorimeter 



that either its total amount can be calculated^ or it can be 
weighed as later described. To avoid radiation errors, the 
calorimeter should be well covered with non-conducting 



330 Steam Engineering 

material. This instrument is not limited in capacitj^ theo- 
retically^ but if the amount of moisture is very large, the 
readings should be checked by passing the discharged steam 
through a throttling calorimeter; that is, a small separator 
should be used between the steam pipe and a throttling 
calorimeter, and the sum of the percentages obtained from 
the two instruments be taken as the moisture in the steam. 
In the separating calorimeter, the amount of steam 
passing through the orifice can be determined by Napier's 
empirical formula, 

pa 
Pounds of steam Der second= — 

70 

In which p= absolute pressure in pounds per square inch, 
and a=area of orifice in square inches. 

There is liability of considerable error in determining 
the area of such small orifices, and further, the flow of 
steam soon wears the orifice larger. A more accurate 
method of determining the weight of steam passing through 
is to convey it through a hose into a barrel of water resting 
on a platform scale. The weight of the barrel and con- 
tained water having been noted before and after the steam 
is run in, the difference is the weight of steam condensed. 
The moisture caught in the separating calorimeter can be 
weighed in the same way. If TF is the weight of steam 
condensed, w the weight of moisture from the separating 
calorimeter, and x the per cent of moisture in the steam, 
then 

lOOw; 
x= • 19} 

Location of Sampling Nipple. The principal source of 
inaccuracv in calorimeter determinations is failure to secure 



""Evaporation Tests 331 

an average sample of steam. It is extremely doubtful 
whether such a sample is ever secured. To diminish the 
liability of error the instrument should be located as near 
as possible to the point where the sample is drawn off. 

Taking an Observation, Locate th'S sampling nipple as 
above directed^ attach the instrument as close to it as pos- 
sible^ and cover all exposed parts to prevent radiation. If 
the throttling calorimeter be used^ locate the ste^m gauge 
on the pressure side^ and the thermometer on the expansion 
side. To take an observation, note simultaneously the 
gauge reading and the thermometer reading, and from 
these the content of moisture may be determined by use of 
formula [7]. If the separating calorimeter be used, attach 
to the separator outlet a piece of hose which terminates in 
a vessel of water on a platform scale graduated to read to 
1/100 of a pound. Similarly connect the steam outlet to 
another vessel of water resting on an equally sensitive 
scale. Note in each case the weight of each vessel includ- 
ing the water it contains. When ready to take an obser- 
vation, blow out the instrument thoroughly, so there will 
be no water in the separator. Then simultaneously close 
the separator drip, and insert the steam hose into its 
vessel of water. When the separator has accumulated a 
sufficient quantity of water, close the valve at the main 
steam pipe, thus cutting off the supply of steam to the 
instrument, remove the steam hose from the vessel of water 
into which it was inserted, and empty the separator water 
into its vessel on the scale. Note the final weight of each 
vessel and contents, then the differences between final, 
and original weights will be respectively, the weight of 
moisture collected by the separator, and the weight of 
steam from which the moisture was taken, hence the pro- 
portion of moisture can be computed from formula [9]. 



332 Steam Engineering 

Before taking any calorimeter observations^, steam should 
be allowed to flow through freely until the instrument is 
thoroughly heated up. 

Moisture in the Coal. This can generally be obtained 
from the reports of the geologist of the state in which the 
coal is mine.d^ or from the dealer^ although the former is 
the most reliable. The percentage of moisture must be 
deducted, from the total weight of coal in figuring the 
weight of combustible. 

Measuring the Chimney Draft. A good draft is indis- 
pensable for obtaining economical results in an evapora- 
tion test. The draft can be easily regulated by a damper 
to suit the conditions. Chimney draft is ordinarily meas- 
ured by a draft gauge connected with the smoke flue near 
the chimney. The usual form of draft gauge is a glass 
tube bent in the shape of the letter U. (See Fig. 106.) 
One leg is connected to the flue by a small rubber hose, 
while the other is open to the atmosphere. The tube is 
partly filled with water, which will, when there is no draft, 
stand at the same height in both legs. When connected 
to the chimney or flue the suction will cause the water in 
the leg to which the hose is attached to rise, while the level 
of the water in the other leg will be equally depressed, and 
the extent of the variation in fractions of an inch is the 
measure of the draft. Thus the draft is referred to as 
being .5, .7 or .75 inches. The draft should not be less 
than .5 inches in any case to insure good results. 

The Barrus draft gauge is illustrated in Fig. 107. It 
consists of a U-tube made of i/2-inch glass, surmounted 
by two larger tubes, or chambers, each having a diameter 
of 2y2-inch. Two different liquids which will not mix, 
and which are of different color, are used. The movement 



Evaporation Tests 



333 



of the line of demarcation is proportional to the difference 
in the areas of the chambers and of the U-tube connecting 
them below. The liquids generally employed are alcohol 
colored red and a certain grade of lubricating oil. A 




/\/\ 



(D 






Fig. 106 



Fig. 107 
baerus' draft gauge 



multiplication varying from eight to ten times is obtained 
under these circumstances; in other words, with i/4-inch 
draft the movement of the line of demarcation is some 2 
inches. The instrument is calibrated by referring it to 
the ordinary U-tube gauge. 



334 



Steam Engineering 



Ellisons Gauge. In this form of gauge the lower por- 
tion of the ordinary U-tube has been replaced by a tube 
slightly inclined to the horizontal^ as shown in Fig. 108. 
By this arrangement any vertical motion in the left hand 
upright tube causes a very much greater travel of the 
liquid in the inclined tube^ thus permitting extremely 
small variation in the draft pressure to be read with fa- 
cility. 

The gauge is first leveled by means of the small level 
attached to it^ both legs being open to the atmosphere. 
The liquid is then adjusted (by adding to or taking from 




Fig. 108 
ellison's draft gauge outline 



it) until its meniscus rests at the zero point on the right. 
The left hand leg is then connected to the source of draft 
by means of a piece of rubber tubing. Under these cir- 
cumstances, a rise of level of one inch in the left hand 
vertical tube causes the meniscus in the inclined tube to 
pass from the point to 1.0. The scale is divided into 
tenths of an inch, and the subdivisions are hundredths of 
an inch. 

The right hand leg of the instrument bears two marks. 
By filling the tube to the lower of these the range of the 
instrument is increased one-half inch, i. e., it will record 
draft pressures from to 11/4 inches. Similarly, by filling 



Evaporation Tests 335 

to the upper mark, the range is increased to 2 incher-: 
When so used the observed readings in the scale are to be- 
increased by one-half or one-inch, as the case may be. 

Th6 makers recommend the use of a non-drying oil 
for the liquid, usually a 300° test refined petroleum, but 
"water suffices for all practical purposes. 

Flue Gas Analysis. The object of the flue-gas analysis 
is to determine from a sample of the gas the amount of 
excess air admitted, the degree of completeness of the com- 
bustion of the carbon, and the amount and distribution of 
the heat losses due to the excess air and incomplete com- 
bustion. The quantities actually determined by the analy- 
sis are the relative proportions of carbon dioxide (CO2), 
carbon monoxide (CO), and oxygen (0) in the gases. 
Although the analysis does not directly determine the 
amount of nitrogen present in the flue-gases, yet its actual 
amount, as well as that of the air supply, may readily be 
ascertained by calculation. When air is drawn through an 
opening, like an ash-pit door, sometimes an anemometer 
can be used for ascertaining the velocity through the area, 
and the air supply be determined by these means. 

A pound of carbon requires for complete combustion, 
2.67 pounds of oxygen, or a volume of 32 cubic feet at 
60° F., and the gaseous product, carbon dioxide (COo), 
when cooled occupies precisely the same volume as the oxy- 
gen, viz., 32 cubic feet. If the oxygen is mixed with nitro- 
gen in the same proportion as it is found in air (20.91 
and 79.09 N), the volume of the carbon dioxide (CO2) 
after combustion, and also its proportion to nitrogen, is 
the same as that of the oxygen; hence, for complete com- 
bustion of carbon, with no excess of air, the volumetric 
analysis of the flue gases is. 



336 Steam Engineering 

Carbon dioxide GO2=20.91% 

. Carbon monoxide CO =None 

Oxygen =N"one 

Mtrogen N =79.09% • 

If the supply of air is in excess of that required to supply 
the oxygen needed, the combined volumes of the carbon 
dioxide and oxygen are still the same as that of the oxygen 
before combustion; consequently^ for the complete com- 
bustion of pure carbon, the sum of the percentages by vol- 
ume of the carbon dioxide and oxygen in the flue gases 
must always be 20.91, no matter what the supply of air 
may be. 

Carbon monoxide (CO) produced by imperfect com- 
bustion of carbon, occupies twice the volume of the oxygen 
entering into its composition, and renders the volume of 
the flue gases greater than that of the air supply in the 
proportion of 

100 
iience 

100—1/2 the % of Co' 
when pure carbon is the fuel, the sum of the percentages 
of carbon dioxide, oxygen, and one-half the carbon mon- 
oxide must be in the same ratio to the nitrogen as is oxy- 
gen in the air, viz. 20.91 to 79.09. 

Orsat Apparatus. The analysis of the flue-gases is best 
made for practical purposes by means of the Orsat appara- 
tus shown in Fig. 109. The operation is as follows: 
Exactly 100 cc of the gas sample are drawn into the 
graduated measuring burette. A, and then passed in suc- 
cession into the U-form absorbing vessels, D, E, P, each 
time being returned to and measured in A. In passing 
into the U-shaped vessels, the gas displaces the liquid 
contained therein, driving it up into the other legs. A 



Evaporation Tests 



337 



portion of the fluids, however, adheres to the glass tubes 
placed in the vessels for that purpose, and comes in inti- 
mate contact with the gas. Each vessel absorbs a different 
constituent. D is filled with a solution of potassium 
hydroxide and takes up the carbon dioxide; E contains 




Fig. 109 
orsat apparatus for flue-gas analysis 

pyrogallic acid, which removes the oxygen ; and F absorbs 
the carbon monoxide in a solution of cuprous chloride. 
The reduction in volume measured in A gives the per- 
centage of each constituent gas. 



338 Steam Engineering 

The connections to A are made through the glass stop 
cocks M, and the capillary tube C. The movement of the 
gases is produced by lowering or raising the bottle L^ which 
is connected to the lower part of A by the rubber tube S, 
and is partially filled with water. When a measurement 
is taken^ the level of the water in A and L must be the 
same, so that all measurements are taken at atmospheric 
pressure. A constant temperature of the gas in A is main- 
tained by the water in the surrounding cylinder shown. 

The sample is drawn into the apparatus through the 
cock B, which also serves to connect the capillary tube to 
the atmosphere, the latter connection being through the 
spindle of the cock ; this permits the removal of any excess 
of gas above 100 cc that may have been drawn into A. Be- 
fore the sample is drawn, the vessels D, E and F should 
have their respective liquids raised to the cocks M which 
can then be closed, and the atmospheric pressure acting 
through the other leg, which is open, will keep them filled. 
The burette A and the capillary tubes should be filled with 
water up to the cock B. All this can easily and quickly 
be done by raising and lowering L, and opening and closing 
cocks M and B. The absorption of oxygen and carbon 
monoxide is very slow, and the gas should be passed back 
and forth a number of times until a reduction of volume 
is no longer indicated. 

As the pressure of the gases in a flue is less than the 
atmospheric pressure, they will not, of themselves, flow 
through the rubber or metal tubing connecting to the 
analyzing apparatus; but by filling the instrument two or 
three times and discharging it into the atmosphere through 
cock B, the air can be removed from the connecting tubing 
and a sample of the gas be obtained. For rapid work, an 



Evaporation Tests 339 

aspirator can be used for drawing the gas from tlie tube 
in a constant stream. If this is used there is less danger 
of an admixture of air. It is sometimes desirable to take 
a sample that represents an average during half an hour, 
or an hour^, and in this case a metal, or glass vessel with 
a stop-cock at both top and bottom, and filled with water, 
can be connected through the upper stop-cock to the flue, 
and the bottom cock then be opened. The water will 
gradually drip out, drawing the gas into the vessel. The 
time taken to fill it can be regulated by the lower cock. 

The result of a flue-gas analysis depends both on the 
manner and time of taking the sample, and to get at the 
average composition of the gas, a number of determina- 
tions should be made on samples from different parts of 
the flue. 

The analysis made by the-Orsat apparatus is volumetric; 
if the analysis by weight is required it can be found from 
the volumetric analysis as follows: 

Multiply the percentages by volume by the molecular 
weight of the gas/ and divide by the sum of all the prod- 
ucts; the quotient will be the percentage by weight. 

The molecular weights are as follows : 

Carbon dioxide 44 

Carbon monoxide 28 

Oxygen 32 

Nitrogen 28 

Calculations for Efficiency of the Plant. Having thus 
successfully conducted the test to its close, and being armed 
with all the data heretofore noted, the engineer is now 
ready to compute the results. 

If the test is made for the purpose of determining the 
efficiency of the boiler and setting as a whole, including 



•340 Steam Engineering 

grate^ chimney draft, etc., then the result must be based 
upon the number of pounds of water evaporated per pound 
of coal. This latter phrase includes not only the purely 
combustible matter in the coal, but the non-combustible 
also, as ash, moisture, etc. Some varieties of western coal 
contain as high as 12 to 14 per cent, of moisture, and the 
ability of the furnace to extract heat from the mass is to 
be tested, as well as the ability of the boiler to absorb and 
transmit that heat to the water. Therefore the efficiency 
of the boiler and furnace= 

Heat absorbed per pound of coal. 
Heating value of one pound of coal. 

Efficiency of the Boiler. The heating surface of the 
boiler must transmit heat from the hot furnace gases on 
one side, to the water on the other. This transmission of 
*heat is very rapid through the metal of the boiler, but the 
accumulation of scale on the interior, and soot on the ex- 
terior surfaces greatly obstructs the flow of heat and renders 
the heating surface inefficient. 

If the test is to determine the efficiency of the boiler 
itself as an absorber of heat, then the combustible alone 
must be considered in working out the final result. Thus, 

Efficiency of boiler= 

Heat absorbed per pound of combustible. 
Heating value of one pound of combustible. 

When making a series of tests for the purpose of com- 
paring the economical value of different varieties of coal, 
the conditions should be as nearly uniform as possible; 
that is, let the tests be made under ordinary working con- 
ditions, and with the same boiler or boilers, and if possible 
with the same fireman. 



Evaporation Tests 341 

The following is a record of one of many evaporation 
tests made by the author^ and is introduced here for the 
purpose of illustrating methods of computing xhe results 
to be obtained from the various data. The rather large 



Date of test 

Duration of test, 12 hours. 
Boiler, return tubular, 72 in. diameter, 18 ft. long, 62-4J in. tubes. 

Kind of coal, Pocahontas; average steam pressure 85 lbs. 

Weight of coal consumed 11,100 lbs. 

Weight of water apparently evaporated 107,187 lbs. 

Weight of dry ash returned 8.1 per cent.= 900 lbs. 

Moisture in the coal 2.0 per cent.= 222 lbs. 

Moisture in the steam 1.0 per cent.= 1,071 lbs. 

Dry coal corrected for moisture 10,878 lbs. 

Weight of combustible 9,978 lbs. 

Water corrected for moisture in the steam 106,116 lbs. 

Water evaporated into dry steam, from and at 212° 117,788 lbs. 

Water evaporated per lb. of coal, actual conditions 9.65 lbs. 

Water evaporated per lb. of coal, from and at 212° 10.61 lbs. 

Water evaporated per lb. of combustible, from and at 212° . . 11.81 lbs. 

Water evaporated per lb. of dry coal, from and at 212° 10.82 lbs. 

Water evaporated per hr. per sq. ft. of heating surface 6.22 lbs. 

Coal burned per sq. ft. of grate surface per hour 25 lbs. 

Horsepower developed by boiler during test 284.5 

Temperature of feed water, average 141° 

Temperature of chimney gases, average 400° 

Square feet of grate surface 36 

Square feet^ of heating surface 1,576 

Ratio of grate surface to heating surface 43.7 



quantity of coal burned per square foot of grate surface 
per hour (25 pounds) is owing to the fact that the boiler 
was run to its full capacity, the coal burning clean, and 
forming no clinker. The chimney draft also was excep- 
tionally good, giving a large unit of evaporation per square 
foot of heating surface per hour. The low temperature of 
the escaping gases is due to the fact that they were returned 
over the top of the boiler before passing to the chimney. 

The results obtained will be taken up in their regular 
order beginning with, first, water evaporated into dry steam 
from and at 212^. As it may be of benefit to some, a 
short definition of the meaning of the above expression is 
here given. 



342 Steam Engineering 

The term ^^equivalent evaporation/' or the evaporation 
from and at 212°^ assumes that the feed water enters the 
boiler at a temperature of 212° and is evaporated into steam 
at 212° temperature and at atmospheric pressure. As for 
instance^ if the top man hole plate were left out^ or some 
other large opening in the steam space allowed the steara 
to escape into the atmosphere as fast as it was generated. 
Owing to the variation in the temperatures of the feed 
water used in different tests, and also the variation in the 
steam pressure^ it is absolutely necessary that the results 
of all tests be brought by computation to^the common basis 
of 212° in order to obtain a just comparison. 

The process by which this is done is as fallows: Ee- 
ferring to the record of the test it is seen that the steam 
pressure average was 85 pounds gauge pressure^ or 100 
pounds absolute^ and that the temperature of the feed water 
was 141°. Eef erring again to Table 17, physical proper- 
ties of steam, it will be seen that in a pound of ^steam at 
100 pounds absolute pressure there are 1,181.8 heat units, 
and in a pound of water at 141° temperature there are 
109.9 heat units. It therefore took 1,181.8—109.9= 
1,071.9 heat units to convert one pound of feed water at 
141° into steam at 85 pounds pressure. To convert a pound 
of water at 212° into steam at atmospheric pressure, and 
212° temperature requires 965.7 heat units, and the 1,071.9 
heat units would evaporate 1,071.9-1-965.7=1.11 pounds 
Avater from and at 212°. The 1.11 is the factor of evapora- 
tion for 85 pounds gauge pressure and 141° temperature 
of feed water, and by multiplying ^Vater corrected for 
moisture in the steam'' (see record of test), 106,116 pounds, 
by 1.11, the weight of water which could have been evapo- 
rated into steam from and at 212° is obtained, which is 



Evaporation Tests 



343 



117,788 pounds. The factor of evaporation is based upon 

the steam pressure and the temperature of the feed water 

in any test and the formula for ascertaining it is as fol- 

H— h 

lows: Factor= , in which H=total heat in the 

965.7 

steam and h=total heat in the feed water. It is used in 

shortening the process of finding the evaporation from and 

at 212°, and Table 26 gives the factor of evaporation for 

various pressures and temperatures. 

Table 26 
factors of evaporation. 



^3 




in 


03 

J3 


CO 




CO 

X3 


CO 


CO 


(0 

J3 


^2 


|i 


gs 


|i 


|i 


|i 




bCrH 


i 










U 






u 


C3 . 
u 


CO 


OS 

u 
Ph 


212° 


1.027 


1.030 


1.032 


1.035 


1.037 


1.039 


1.041 


1.043 


1.047 


200° 


1.039 


1.042 


1.045 


1.047 


1.050 


1.052 


1.054 


1.056 


1.059 


191° 


1.049 


1.052 


1.054 


1.057 


1.059 


1.061 


1.063 


1.065 


1.069 


182° 


1.058 


1.061 


1.064 


1.066 


1.069 


1.071 


1.073 


1.075 


1.078 


173° 


1.067 


1.070 


1.073 


1.076 


1.078 


1.080 


1.082 


1.084 


1.087 


164° 


1.077 


1.080 


1.083 


1.085 


1.087 


1.090 


1.091 


1.093 


1.097 


152° 


1.089 


1.092 


1.095 


1.098 


1.100 


1.102 


1.104 


1.106 


1.109 


143° 


1.099 


1.102 


1.105 


1.107 


1.109 


1.111 


1.113 


1.115 


1.119 


134° 


1.108 


1.111 


1.114 


1.116 


1.119 


1.121 


1.123 


1.125 


1.128 


125° 


1.118 


1.121 


1.123 


1.126 


1.128 


1.130 


1.132 


1.134 


1.137 


113° 


1.130 


1.133 


1.136 


1.138 


1.140 


1.143 


1.145 


1.146 


1.150 


104° 


1.138 


1.142 


1.145 


1.148 


1.150 


1.152 


1.154 


1.156 


1.159 


95° 


1.149 


1.152 


1.154 


1.157 


1.159 


1.161 


1.163 


1.165 


1.169 


86° 


1.158 


1.161 


1.164 


1.166 


1.169 


1.171 


1.173 


1.174 


1.178 


77° 


1.167 


1.170 


1.173 


1.176 


1.178 


1.180 


1.182 


1.184 


1.187 


65° 


1.180 


1.183 


1.186 


1.188 


1.190 


1.192 


1.194 


1.196 


1.200 


56° 


1.189 


1.192 


1.195 


1.197 


1.200 


1.202 


1.204 


1.206 


1.209 


47° 


1.199 


1.201 


1.204 


1.207 


1.209 


1.211 


1.213 


1.215 


1.218 


38° 


1.208 


1.211 


1.214 


1.216 


1.218 


1.220 


1.222 


1.224 


1.228 



Second^ water evaporated per pound of coal actual con- 
ditions=water apparently evaporated divided by coal con- 
sumed=9. 65 pounds. No accurate estimate regarding the 
quality of the coal or the efficiency of the boiler can be 
made from this figure (9.65 pounds). It can be used, 



344 Steam Engineering 

however^ in estimating the cost of fuel for generating the 
steam; as, for instance, if the boiler is supplying steam to 
an engine that uses 30 pounds of steam per house-power 
per hour, it will require 30^9.65=3.1 pounds of coal per 
horse-power per hour ; the "actual conditions'^ under which 
the boiler is being operated being the pressure of steam 
required by the engine and the temperature of the feed 
water. 

Third, water evaporated per pound of coal from and at 
212°^water evaporated into dry steam from and at 212° 
-f-coal consumed= 10.61 pounds. This figure is the proper 
one to use in comparing the relative economic values of 
different varieties of coal tested with the same boiler or 
boilers. 

Fourth, water evaporated per pound of combustible from 
and at 212 °=water ..evaporated into dry steam from and 
at 212° -^weight of combustible=11.81 pounds. This re- 
sult is the one to be used for ascertaining the efficiency of 
the boiler, and the percentage of efficiency is found by 
dividing the heat absorbed by the boiler per pound of com- 
bustible by the heat value of one pound of combustible. 
The average heat value of bituminous and semi-bituminous 
coals is not far from 15,000 heat units per pound of com- 
bustible. In the evaporation of 11.81 pounds of water 
from and at 212° the heat absorbed was 11.81X965.7= 
11,404.9 heat units. The efficiency of the boiler therefore 
was 

11,404.9X100 

=76 per cent. 

15,000 

In like manner to ascertain the efficiency of the boiler 
and furnace as a whole, the water evaporated from and 
at 212° per pound of coal is taken. Thus 10.61X965.7 



Evaporation Tests 345 

=10,246 heat units absorbed from each pound of coal. 

Now assuming that there were 13,500 heat units in each 

pound of the coal used in the test, the per cent of efficiency 

of boiler and furnace was 

10,246X100 

=75.9. 

13,500 

Fifth, water evaporated per pound of dry coal from 
and at 212°^ water evaporated into dry steam from and 
at 212° divided by coal corrected for moisture. Thus, 
117,788-f-10.878=10.82 pounds. This result is useful 
for calculating the results of tests of the same grade of 
coal, but differing in the degree of moisture in each. 

Sixth. Boiler horse-power. The latest decision of the 
American Society of Mechanical Engineers (than whom 
there is no better authority) regarding the horse-power of 
a boiler is as follows: '^^The unit of commercial horse- 
power developed by a boiler shall be taken as 34% nnits 
of evaporation per hour. That is, 34^/2 pounds of water 
evaporated per hour from a feed temperature of 212° 
into steam of the same temperature. This standard is 
equivalent to 33,317 B.T.U. per hour. It is also practically 
equivalent to an evaporation of 30 pounds of water from a 
feed water temperature of 100° P. into steam of 70 pounds 
gauge pressure.^^ 

According to this rule the horse-power developed by the 
boiler during the test under consideration:=water evap- 
orated into dry steam from and at 212°, 117,788 pounds 
4-13 hours-f-34.5=284.5 horse-power. 



346 Steam Engineering 

QUESTIONS AND ANSWERS. 

267. What is the primary object of an evaporation test? 
. Ans, To ascertain how many pounds of water the boilers 

are evaporating per pound of coal burned. 

268. What other important points relative to boiler 
operation may be determined by these tests ? 

Ans. There are four. First — To determine the efficiency 
of the plant as an apparatus for the consumption of fuel, 
and the evaporation of water. Second — To determine the 
relative economy of different varieties of coal^ and other 
fuels. Third — To determine whether or not the boilers 
are being operated as economically as they might be. 
Fourth — To determine whether the boilers are being over 
worked. 

269. In what condition should the testing apparatus 
be maintained? 

Ans. In first-class condition, ready to be used at any 
time for making a test. 

270. What should be done with the boiler, and all of 
its appurtenances preparatory to making a test? 

Ans, They should be put in good condition, by clean- 
ing, etc. 

271. How should the boiler under test be operated 
during the test? 

Ans, At its full capacity. 

272. Where should the water level be at the beginning, 
and close of the test ? 

Ans. At the height ordinarily carried, and its position 
should be marked by tying a cord around one of the guard 
rods of the gauge glass. 

273. How long should the test last? 
Ans. About 10 hours. 



Questions and Answers 347 

274. How is the percentage of moisture in the steam 
determined ? 

Ans. By means of the calorimeter. 

275. How many^ and what kind of calorimeters are 
used for this purpose? 

Ans. Two. The throttling calorimeter^ and separating 
calorimeter. 

276. Upon what principle does the throttling calori- 
meter act? 

Ans, Upon the principle of temperatures. 

277. How does the separating calorimeter act? 

Ans. It mechanically separates the water from a known 
volume of steam passing through it. 

278. In what other manner may the condition of steam 
regarding its dryness be approximated? 

Ans, By observing its appearance as it issues from a 
pet cock, or other small opening. 

279. How will steam containing 1 or 2 per cent of 
moisture appear under such conditions ? 

Ans, It will be transparent close to the orifice from 

which it issues. 

280. How is the chimney draft measured? 
Ans, By means of a draft gauge. 

281. What is the usual form of draft gauge? 
Ans, A glass tube bent in the shape of the letter U. 

282. Describe the action of a draft gauge. 

Ans, One leg of the U tube is connected to the chimney 
by a small rubber hose. The other leg is open to the at- 
mosphere. The tube is partly filled with water^ which 
when there is no draft will stand at the same height in 
Loth legs. 



348 Steam Engineering 

283. When there is a draft and the rubber hose is con- 
nected to the chimney how is the water in the U tube 
affected ? 

Ans. The draft suction causes the water in the leg to 
which the hose is connected^ to rise while the level of the 
water in the other leg will be equally depressed. 

284. How is the intensity of the draft thus estimated? 
Ans, In fractions of an inch^ .5^ .7 or .75 inches. 

285. What is the object of flu6 gas analysis? 

Ans, There are three. First- — To determine the amount 
of excess air admitted to the furnace. Second — To de- 
termine the character of the combustion. Third — To as- 
certain the heat losses. 

286. What weight of oxygen is required for the com- 
plete combustion of one pound of carbon? 

Ans. 2.67 pounds. By volume^ 32 cubic feet. 

287. What gaseous combination is produced by com- 
plete combustion? 

Ans, Carbon dioxide (CO2). 

288. What is the result of imperfect combustion? 
Ans. Carbon monoxide (CO). 

289. How is the efficiency of the boiler and furnace 
ascertained through an evaporation test? 

Ans. By weighing the coal consumed and the water 
evaporated during a certain number of hours and dividing 
the number of pounds of water evaporated by the number 
of pounds of coal consumed. This will give number of 
pounds water evaporated per pound o± coal. 

290. What is meant by the term ^^equivalent evapora- 
tion?^^ 

Ans. It assumes that the feed water enters the boiler 
at a temperature of 212°^ and is evaporated into steam at 
212° and at atmospheric pressure. 



Questions and Answers 349 

291. Why is this standard necessary in evaporatio]q. 
tests ? 

Ans. Because of the variations in the temperature of 
the feed water used in different tests. 

292. What is meant by boiler horse-power? 

Ans. The evaporation of 341^ pounds water from a 
feed temperature of 212^ into steam of the same tempera- 
ture; or the evaporation of 30 pounds water from a feed 
temperature of 100° into steam at 70 pounds gauge pres- 
sure. 

293. What is meant by the expression ^^total heat of 
evaporation ?'^ 

Ans, The sum of the sensible heat plus the latent heat, 
at boiling point. 

294. What is steam in its relation to the engine? 
Ans. It is merely a vehicle for transferring the neat 

energy from the boiler to the engine shaft. 



Steam Engines 




Fig. 110 
eeynolds combined vertical and horizontal engine 12,000 

HORSE-POWER CYLINDERS, 44x88x60. 

Built by Allis-Chalmers Company 

Steam engines may be divided into two general classes, 
viz., simple and compound. 

A simple engine may be either condensing or non-con- 
densing, but its leading characteristic is, that the steam is 

351 



352 Steam Engineering 

used in but one cylinder^ and from thence it is exhausted 
either into the atmosphere or into a condenser. 

A compound engine is one in which the steam is made 
to do work in two or more cylinders before it is allowed 
to exhaust;, and this class of engine may be either condens- 
ing or non-condensing. 

In a non-condensing engine the pressure of the atmos- 
phere^ amounting to 14.7 pounds per square inch at sea 
level;, is constantly in resistance to the motion of the piston. 
Therefore the exhaust pressure cannot fall below the atmos- 
pheric pressure^ and is generally from two to five pounds 
above it^ caused by the resistance of bends and turns in the 
exhaust pipe^ or other causes which tend to retard the free 
passage of the steam. 

The advantage^ from an economical point of view^, of 
exhausting the steam into a condenser in which a vacuum 
is maintained;, will be fully set forth in the section on 
Indicator Work. 

CONDENSERS. 

Condensers are of two classes^ viz.^ jet condensers and 
surface condensers. 

In a jet condenser^ the steam is exhausted into an air- 
tight iron vessel of any convenient shape^ generally cylin- 
drical and of suitable size^ and is there condensed by com- 
ing in contact with a jet of cold water, admitted in the 
form of a spray. The air pump, which also maintains a 
vacuum in the condenser, draws this water, together with 
the condensed steam, away from the condenser. 

The surface condenser, like the jet condenser, consists 
of an air-tight iron vessel, either CA^lindricat or rectangular 
in shape, but unlike the jet condenser, it is fitted with a 



Condensers 353 

large number of brass or copper tubes of small diameter, 
through which cold water is forced by a pump^ called a 
circulating pump. A vacuum is also maintained in the 
body of the condenser by the air pump, and the steam 
exhausting into this is condensed by coming in contact 
with the cool surface of the tubes. Or^ as is often the case, 
the exhaust steam passes through the tubes in place of 
around them, and the condensing water is forced into and 
through the body of the condenser, the vacuum in this case 




Fig. Ill 

CROSS COMPOUND DIRECT CONNECTED CORLISS ENGINE, ALLIS- 
CHALMERS COMPANY 

being maintained in the tubes. Owing to the fact that in 
a surface condenser the steam does not mix with the water, 
a larger quantity of condensing water is required than in 
a jet condenser, but on the other hand, an advantage is 
gained by having the pure water of condensation ; in other 
words, the condensed steam, which may 'be returned to the 
boilers along with the regular feed water supply, and will 
greatly aid in preventing the formation of scale, while the 
water of condensati'^'n ?^^- it comes from a jet condenser, 



354 Steam Engineering 

being mixed with oil and other impurities, is not, as a rule, 
suitable to be fed to boilers. 

There are many diJBEerent types of jet condensing ap- 
paratus, in some of which no air pump is used ; their action 
being based somewhat upon the principle of the injector 
used for feeding boilers. In this type of jet condenser 
the supply of condensing water is drawn from outside pres- 
sure, either from an overhead tank or other source, and 
passing into an annular enlargement of the exhaust pipe, 
is discharged downwards in the form of a cylindrical sheet 




Fig. 112 
tandem compound engine, buckeye engine company 

of water into a nozzle which gradually contracts. The 
exhaust steam, entering at the same time, is condensed, 
and the contracting neck of the cone shaped nozzle gradu- 
ally brings the water to a solid jet, and it rushes through 
the nozzle with a velocity sufficient to create a vacuum. 
This type of condenser can only be used where the dis- 
charge pipe has a free outlet. 

The jet condenser with air pump attached is the most 
reliable as well as economical for general purposes, for the 
reason that with this type the supply of condensing water 
may be drawn from a well or other source lower than the 



Condensers 



355 



level of the condenser. These condensers are also generally 
fitted with a ^"^force injection/^ as it is called^ which is 
simply a connection between the condenser and water main 




Fig. 113 
knowles jet condenser 



or tank, for the purpose of letting cold water into the con- 
denser to condense the exhaust steam when starting the 
engine, and thus aid in forming a vacuum. When a good 



356 Steam Engineering 

vacunm has been established and the engine is running np 
to speedy the force injection may be shut off;, and the water 
will flow into the condenser from the well by suction. The 
above refers to engines in which the air pump receives its 
motion directly from the engine.^ 

Another type of jet condensing apparatus is the inde- 
pendent air pump and condenser^ which is still better, for 
the reason that the air pump, which is simply an ordinary 
double acting steam pump, may be started independently 
of the engine, and, in fact, before rthe engine is started, 
thus creating a vacuum in the condenser, and greatly facili- 
tating the starting of the engine. Another great advantage 
in the independent condensing apparatus is, that there is 
not so much danger of the water backing up into the 
cylinder in case of a sudden shut down of the engine, be- 
cause the air pump may be kept in operation, thus relieving 
the condenser of water* whereas, if the air pump gets its 
motion from the engine, it will of course stop when the 
engine stops, and unless the injection water is shut off 
immediately after closing the throttle there is great danger 
of the cylinder becoming flooded with water, resulting very 
often in a broken cylinder head, or a bent piston rod. 

The quantity of water required to condense the exhaust 
steam of an engine is determined by three factors : First, 
the density, temperature ^nd volume of the steam to be 
condensed in- a given time; second, the temperature of the 
overflow or discharge, and third, the temperature of the 
injection water. For instance, the temperature of the in- 
jection water may be 35° in the winter and 70° in the 
summer. Or it may be desired to keep the overflow at as 
high a temperature as possible for the purpose of feeding 
the boilers. Again, the pressure, and consequently the 



Gvndensers ' 357 

temperature of the exhaust steam as it enters the condenser, 
varies with different engines, and often with the same en- 
gine, according as the load is light or heavy. Therefore 
the only accurate method of estimating the amount of con- 
densing water required per minute or per hour, under any 
and all conditions, is to first ascertain the weight of water 
required to condense one pound weight of steam at the tem- 
perature and pressure at which the steam is being ex- 




FiG. 114 

WORTHINGTON SURFACE CONDENSER, WITH AIR AND CIRCULATING 

PUMP 

hausted. In these calculations the total heat in the steam 
must be considered. This means not only the sensible 
heat, but the latent heat also. 

The formula for solving the above problem may be ex- 

H— T 

pressed as follows : =W, in which 

T— I 

H=total heat in the steam, 
T=temperature of the overflow, 



358 



Steam Engineering 



I = temperature of the injection water^ 

W=weight of water required to condense one pound 
weight of steam. 

To illustrate^ suppose the absolute pressure of the ex- 
haust^ as shown by the indicator diagram^ is 7 pounds. 
Eef erring to Table 17^ it will be seen that the total heat 
in steam at 7 pounds absolute is 1135.9 heat units. As- 
sume the temperature of the overflow to be 110^, which is 




Fig. 115 
siphon condenser 

as high as is consistent with a good vacuum. Now the 
total heat to be absorbed from each pound weight of steam 
in this case would be 1135.9—110=1025.9 B. T. U. 

Suppose the temperature of the condensing water to 
be 55° and the temperature of the overflow being 110°, 
there will be 110° — 55° =55° of heat absorbed by each 
pound of water passing into, and through the condenser, 
and the number of pounds of water required to condense 



Condensers 359 

one pound weight of steam under the above conditions 

will equal the number of times 55 is contained in 1025.9. 

Expressed in plain figures the calculation is 

1135.9_110 

=18.65 pounds. 

110—55 

In order to ascertain the quantity of condensing water 
required per house-power per hour^ it is only necessary to 
know the number of pounds weight of steam consumed by 
the engine per horse-power per hour, as shown by the indi- 
cator diagram, and multiply this by the weight of condens- 
ing water required per pound of steam, as found by the 
above solution. 

Thus, suppose the steam consumption of the engine to 
be 17 pounds per I. H. P. per hour. Then 17X18.65=: 
317.05 pounds per hour, which reduced to gallons=38.2 
gallons. 

Or, if the steam consumption is not known, and the 
weight only of condensing water required per hour is de- 
sired, regardless of the horse-power developed by the en- 
gine, it will be necessary, first, to estimate the total volume 
of steam exhausted per hour and calculate its weight from 
its known pressure. 

Thus, assume the engine to be 24X^8 inches, and the 
R. P. M. to be 80. Then the piston displacement will equal 
area of piston less one-half area of rod multiplied, by length 
of stroke. Eef erring to Table 27, the area of a circle 24 
inches in diameter=452.39 square inches. Suppose the 
piston rod to be 4.5 inches in diameter, its area, according 
:to Table 27, is 15.904 square inches, one-half of which= 
i7.952 square inches. The effective area of the piston now 
becomes 452.39 — 7.952=444.43 square inches, and the pis- 
ton displacement equals 444.43X48=21332.64 cubic inches. 



360 Steam Engineering 

Dividing this by 1728 (number of cubic inches in a cubic 
foot) gives 12.34 cubic feet of piston displacement. The 
total volume of steam exhausted per minute^ therefore, 
will be 12.34X^X80=1974.4 cubic feet. 

The absolute pressure of the exhaust may again be 
assumed to be 7 pounds per square inch. Eeferring to 
Table 17, the weight of one cubic foot of steam at 7 
pounds absolute is .0189 pounds, and the total weight of 
steam exhausted per minute, therefore, would be 19 74.4 X 
.0189=37.3 pounds, and if 18.65 pounds water is required 
to condense one pound of steam, the quantity required per 
minute would be 37.3X18.65=695.8 pounds, or per hour, 
41748 pounds, equal to 5029 gallons. This is at the rate 
of 8.7 pounds, or a little more than one gallon per revolu- 
tion for a 24X1=8 inch, simple condensing engine. Table 
28 gives the quantity of injection water required per revolu- 
tion for different types of condensing engines. 



Condensers 



361 



Table 27 

AREAS AND CIRCUMFERENCES OF CIRCLES. 



Diam. 


Area 


^Circum. 


Diam. 


Area 


Circum. 


.25 

.5 
1.0 
L25 
L5 
2 

2.25 
2.5 


.049 


.7854 


19 


283.529 


59.690 


.1963 


1.5708 


19.25 


291.039 


60.475 


.7854 


3.1416 


19.5 


298.648 


61.261 


1.2271 


3.9270 


20 


314.160 


62.832 


1.7671 


4.7124 


20.25 


322.063 


63.617 


3.1416 


6.2832 


20.5 


330.064 


64.402 


3.9760 


7.0686 


21 


346.361 


65.973 


4.9087 


7.8540 


21.25 


354.657 


06.759 


3 


7.0686 


9.4248 


21.5 


363.0oX 


67.544 


3.25 

3.5 

4 


8.2957 


10.210 


20 ' 


380.133 


69.115 


9.6211 


10.995 


22.25 


388 822 " 


69.900 


12.566 


12.566 


22.5 


397.608 ' 


70.686 


4.25 


14.186 


13.351 


23 


415.4T6 


72.256 


4.5 


15.904 


14.137 


23.25 


424.557 - 


73.042 


5 


19.635 


15.708 


23.5 


433.731 


73.827 


'5.25 


21.647 


16.493 


24 


452.390 , 


75.398 


5.5 


23.758 


17.278 


24.25 


461.864 


76.183 


6 


28.274 


18.849 


24.5 


471.436 


76.969 


6.25 


30.679 


19.635 


25 


490.875 


78.540 


6.5 


33.183 


20.420 


25.25 


500.741 


79.325 


7' 


38.484 


21.991 


25.5 


510.706 


801110 


7.25 


41.282 


22.776 


26 


530.930 


81.681 


7.5 


44.178 


23.562 


26.25 


541.189 


82.467 


8 


50.265 1 


25.132 


26.5 


551.547 


83.252 


8.25 


53.456 


25.918 


27 


572.556 


84.823 


8.5 


56.745 


26.703 


27.25 


583.208 


85.608 


9 


63.617 


28.274 


27.5 


593.958 


86.394 


9.25 


67.200 


29.059 


28 ■ 


615.753 


87.964 


9 5 


70.882 


29.845 


28.25 


626.798 


88.750 


10' 


78.540 


3L416 


28.5 


637.941 


89.535 


10.25 


82.516 


32.201 


29 


660.521 


91.106 


10.5 


86.590 


32.986 


29.25 


671.958 


91.891 


11 


95.033 


34.557 


29.5 


683.494 


92.677 


11.25 


99.402 


35.343 


30 


706.860 


94.248 


11.5 


103.869 


36.128 


30.25 


718.690 


95.033 


12 


113.097 


37.699 


30.5 


730.618 


95.818 


12.25 


117.859 


38.484 


31 


754.769 


97.389 


12.5 


122.718 


39.270 


31.25 


766.992 


98.175 


13 


132.732 


40.840 


3L5 


799.313 


98.968 


13 25 


137.886 


41.626 


32 


804.249 


100.53 


13.5 


143.130 


42.411 


32.25 


816.86 


101.31 


14 


153.938 


43.982 


33 


855.30 


103.67 


14.25 


159.485 


44.767 


33.25 


868.30 


104.45 


14.5 


165.130 


45.553 


33.5 


881.41 


105.24 


15 


176.715 


47.124 


34 


907.92 


106.81 


15.25 


182.654 


47.909 


34.25 


921.32 


107.60 


15.5 


188.692 


48.694 


34.5 


934.82 


108.38 


16 


201.062 


50.265 


35 


932.11 


109.95 


16.25 


207.394 


51.051 


35.25 


975.90 


110.74 


16.5 


213.825 


51.836 


35.5 


0S0.80 


111.52 


17 


226.980 


53.407 


36 


1017.8 


113.09 


17.25 


233.705 


54.192 


86.25 


1032. (]n 


113.88 


17.5 


240.520 


54.978 


36.5 


1046.35 


114.66 


18 


254.469 


56.548 


37 


1075.21 


116.23 


18.25 


261.587 


57.334 


37.25 


1089.79 


117.01 


18.5 


268.803 


58.119 


37.5 


1104.46 


117.81 



362 



Steam Engineering 
Table 27 — continued 



Diam. 


Area 


Circum. 


Diam. 


Area 


Circum. 


38 


1134.11 


119.38 


57 


2551.76 


179.07 


38.25 


1149.08 


120.16 


57.25 


2574.19 


179.85 


38.5 


1164.15 


120.95 


57.5 


2596.72 


180.64 


39 


1194.59 


122.52 


58 


2642.08 


182.21 


39.25 


1209.95 


. 123.30 


58.25 


2664.91 


182.99 


39.5 


1225.42 


124.09 


58.5 


2687.83 


183.78 


40 


1256.64 


125.66 


59 


2733.97 


185.35 


40.25 


1272.39 


126.44 


59.25 


2757.19 


186.14 


40.5 


1288.25 


127.23 


59.5 


2780.51 


186.92 


41 


1320.25 


128.80 


60 


2827.44 


188.49 


41.2b 


1336.40 


129.59 


60.25 


2851.05 


189.28 


41.5 


1352.65 


130.37 


60.5 


2874.76 


190.06 


42 


1385.44 


131.94 


61 


2922.47 


191.64 


42.25 


1401.98 


132.73 


61.25 


2946.47 


192.42 


42.5 


1418.62 


133.51 


61.5 


2970.57 


193.21 


43 


1452.20 


135.08 


62 


3019.07 


194.78 


43.25 


1469.13 


135.87 


62.25 


3043.47 


195.56 


43.5 


1486.17 


136.65 


62.5 


3067.96 


196.35 


44 


1520.53 


138.23 


63 


3117.25 


197.92 


44.25 


1537.86 


139.01 


63.25 


3142.04 


198.71 


44.5 


1555.28 


139.80 


63.5 


3166.92 


199.50 


45 ' 


1590.43 


141.37 


64 


3216.99 


201.06 


45.25 


1608.15 


142.15 


64.25 


3242.17 


201.85 


45.5 


1625.97 


142.94 


64.5 


3267.46 


202.68 


46 


1661.90 


144.51 


65 


3318.31 


204.20 


46.25 


1680.01 


145.29 


65.25 


3343.88 


204,99 


46.5 


1698.23 


146.08 


65.5 


3369.56 


205.77 


47 


1734.94 


147.65 


66 


5421.20 


207.34 


47.25 


1753.45 


148.44 


66.25 


3447.16 


208.13 


47.5 


1772.05 


149.22 


66.5 


3473.23 


208.91 


48 


1809.56 


150.79 


67 


3525.66 


210.49 


48.25 


1828.46 


151.58 


67.25 


3552.01 


211.27 


48.5 


1847.45 


152.36 


67.5 


3578.47 


212.06 


49 


1885.74 


153.93 


68 


3631.68 


213.63 


49.25 


1905.03 


154.72 


68.25 


3658.44 


214.41 


49.5 


1924.42 


155.50 


68.5 


3685.29 


215.20 


50 


1963.50 


157.08 


69 


3739.28 


216.77 


50.25 


1983.18 


157.86 


69.25 


3766.43 


217.55 


50.5 


2002.96 


158.65 


69.5 


3793.67 


218.34 


51 


2042.82 


160.22 


70 


3848.46 


219.91 


51.25 


2062.90 


161.00 


70.25 


3875.99 


220.70 


51.5 


2083.07 


161.79 


70.5 


3903.63 


221.48 


52 


2128.72 


163.36 


71 


3959.20 


223.05 


52.25 


2144.19 


164.14 


71.25 


3987.13 


223.84 


52.5 


2164.75 


164.19 


71.5 


4015.16 


224.62 


53 


2206.18 


166.50 


72 


4071.51 


226.19 


53.25 


2227.05 


167.29 


72.25 


4099.83 


226.98 


53.5 


2248.01 


168.07 


72.5 


4128.25 


227.75 


54 


2290.22 


169.64 


73 


4185.39 


229.34 


54.25 


2311.48 


170.43 


73.25 


4214.11 


230.12 


54.5 


2332.83 


171.21 


73.5 


4242.92 


230.91 


55 


2375.83 


172.78 


74 


4300.85 


232.48 


55.25 


2397.48 


173.57 


74.25 


4329.95 


233.26 


55.5 


2419.22 


174.35 


74.5 


4359.16 


234.05 


56 


2463.01 


175.92 


75 


4417.87 


235.62 


56.25 


1 2485.05 


176.71 


75.25 


4447.37 


236.40 


56.5 


! 2507.19 


177 5 


75.5 


4476.97 


237.19 



Condensers 



363 



Table 27 — continued 



Diam. 


Area 


Circum. 


Diam. 


Area 


Circum. 


76 


4536.37 


238.76 


87.5 


6013.21 


274.89 


76.25 


4566.36 


239.55 


88 


6082.13 


276.46 


76.5 


4596.35 


240.33 


88.5 


6151.44 


278.03 


77 


4656.63 


241.90 


89 


6221.15 


279.60 


77.25 


4686.92 


242.69 


89.5 


6291.25 


281.17 


77.5 


4717.30 


243.47 


90 


6371.64 


282.74 


78 


4778.37 


245.04 


90.5 


6432.62 


284.31 


78.25 


4809.05 


245.83 


91 


6503.89 


285.88 


78.5 


4839.83 


246.61 


91.5 


6573.56 


287.46 


79 


4901.68 


248.19 


92 


6647.62 


289.03 


79.25 


4932.75 


248.97 


92.5 


6720.07 


290.60 


79.5 


4963.92 


249.76 


93 


6792.92 


292.17 


80 


5026.56 


251.33 


93.5 


6866.16 


293.74 


80.5 


5089.58 


252.90 


94 


6939.79 


295.31 


81 


5153.00 


254.47 


94.5 


7013.81 


296.88 


81.5 


5216.82 


256.04 


95 


7088.23 


298.45 


82 


5281.02 


257.61 


95.5 


7163.04 


300.02 


82,5 


5345.62 


259.18 


96 


7238.25 


301.59 


83 


5410.62 


260.75 


96.5 


7313.80 


303.16 


83.5 


5476.00 


262.32 


97 


7389.81 


304.73 


84 


5541.78 


263.89 


97.5 


7466.22 


306.30 


84.5 


5607.95 


265.46 


98 


7542.89 


307.88 


85 


5674.51 


267.04 


98.5 


7620.09 


309.44 


85.5 


5741.47 


268.60 


99 


7697.70 


311.02 


86 


5808.81 


270.17 


99.5 


7775.63 


312.58 


86.5 


5876.55 


271.75 


100 


7854.00 


314.16 


87 


5944.66 


273.32 









Table 28 
quantity of injection water for jet condensers. 

Injection. Temp. 50°. Overflow Temp. 110°. 







WATER 


PER REV. 




Low Press. 


Single Exp. 


Double Exp. 


Triple Exp. 


Cylinder. 


Engines. 


Engines. 


Engines. 




Lbs. 


Galls. 


Lbs. 


Galls. 


Lbs. 


Galls. 


20 in. X 36 in. 


4.2 


.5 


3.9 


.47 


3.6 


.43 


22 ' 


X 36 " 


5.1 


.61 


4.8 


.57 


4.4 


.53 


24 ' 


X 42 " 


7. 


.84 


6.6 


.79 


6. 


.72 


26 * 


X 42 " 


8.3 


1. 


7.8 


.93 


7.2 


.87 


28 * 


X 48 " 


11. 


1.45 


10.4 


1.24 


9.5 


1.14 


30 * 


X 48 " 


12.6 


1.52 


11.7 


1.41 


10.8 


1.3 


32 * 


X 54 " 


16.2 


1.95 


15. 


L81 


13.9 


1.68 


34 * 


X 54 " 


18.3 


2.2 


17.0 


2.05 


15.8 


1.9 


36 * 


X 60 " 


22.8 


2.75 


21.2 


2.55 


19.6 


2.36 


38 ' 


X 60 " 


25.5 


3.07 


23.7 


2.85 


21.9 


2.64 


40 * 


X 66 " 


31. 


3.73 


28.8 


3.45 


26.7 


3.2 


44 * 


X 66 " 


37.5 


4.51 


34.8 


4.2 


32.2 


3.8 


48 . * 


X 72 '' 


48.5 


5.84 


45. 


5.42 


41.7 


5. 


52 * 


X 72 " 


57. 


6.89 


53.1 


6.4 


49.2 


5.9 


56 * 


X 72 " 


66. 


7.9 


61.5 


7.41 


57. 


6.8 


60 ' 


X 72 " 


75.6 


9. 


70.5 


8.5 


65.3 


7.8 


64 " X 72 " 


85. 


10. 


80. 


9.6 74. 


8.9 



364 



Steam Engineering 



Table 29 

SIZE OF AIR-PUMPS— SINGLE ACTING. 
One Stroke of Pump per Rev. of Engine. 





SIZE OF PUMP. 


Low-Press. 
Cylinder. 


Single Exp. 
Engines. 


Double Exp. 
Engines. 


Triple Exp. 
Engines. 


Dia. Stroke 


Dia. Stroke 


Dia. Stroke 


Dia. Stroke 


20 in. X 36 in. 
22 in. X 36 in. 
24 in; x 42 in. 
26 in. X 42 in. 
28 in. X 48 in. 
30 in. X 48 in. 
32 in. X 54 in. 
34 in. X 54 in. 
36 in. X 60 in. 
38 in. X 60 in. 
40 in. X 66 in. 
44 in. X 66 in. 
48 in. X 72 in. 
52 in. X 72 in. 
56 in. X 72 in. 
60 in. X 72 in. 
64 in.-x 72 in. 


15 H in. X 8 in. 
liyV^ in. X 10 in. 
17^ in. X 10 in. 
19^ in. X 10 in. 
221^ in. xlOin. 
21^ in. X 12 in. 
24^ in. X 12 in. 
26^/4 in. X 12 in. 
29^ in. X 12 in. 
31 in. X 12 in. 
34^ in. X 12 in. 
33 >4 in. X 15 in. 
38 in. X 15 in. 
41^ in. X 15 in. 
44^ in. X 15 in. 
47^ in. X 15 in. 
51 in. X 15 in. 


15 in. X 8 in. 
16^ in. X 8 in. 
17^ in. X 10 in. 
18^ in. X 10 in. 
21 ^ in. X 10 in. 
22^ in. X 10 in. 

24 m. X 12 in. 

25 >^ in. X 12 in. 
28 J4 in. xl2in. 
30 in. X 12 in. 
33 in. X 12 in. 
321/^ in. X 15 in. 
37 in, X 15 in. 
40 in. X 15 in. 
43 in. X 15 in. 
461/4 in. X 15 in. 
49Hin. xl5in. 1 


14^ in. X -8 in. 
16^ in. X 8 in. 
IQy, in. X 10 in. 
18 in. X 10 in. 
20M in. X 10 in. 

22 in. X 10 in. 

23 in. X 12 in. 
24^ in. X 12 in. 
21 Ya in. xl2in. 
28^ in. x 12 in. 
31^ in. X 12 in. 
34^ in. xl2in. 
35 >^ in. X 15 in. 
38^ in. X 15 in. 
42 in. X 15 in. 
44^ in. X 15 in. 
47 in. X 15 in. 



Multiple Cylindei' Engines, As has been already ex- 
plained^ a compound engine is one in which the steam is 
made to do work in two or more cylinders^ and the secret 
of success in this type of engine is due to three factors^ 
viz.^ (1) 'a high initial pressure^ (2) the expansion of the 
steam to the greatest extent^ and (3) reducing as much 
as possible the losses caused by cylinder condensation. Prof. 
Thurston has wisely said that '^'Maximum expansion^ as 
nearly adiabatic as practicable^ is the secret of maximum 
efficiency.^^ 

Horizontal — Vertical, Of the se^^eral types of multiple 
expansion engines^ the two cylinder or double expansion' 
engine appears to be best adapted to central power station 
service, owing to the excessive load variation. Figure 110 
shows the horizontal vertical type. It has many advantages, 
especially in large units. First, the low pressure cylinder 



Compound Engines 365 

can be arranged vertically and thereby avoid the excessive 
friction due to the weight of so large a piston; second^ the 
cylinders being arranged one vertical and the other hori- 
zontal and both acting upon the same crank pin^ gives 
four impulses for each revolution of the crank. The cut 
represents a pair of such engines with two cranks^ the 
cranks being keyed to one shaft and at right angles to each 
other make eight impulses for each revolution^ a still " 
greater improvement in turning effect. This type of en- 
gine is particularly valuable in electric service^ with the 
armature between the engines^ and ^makes a very compact 
and desirable arrangement. 

Cross- Compound. A, cr6ss compound engine consists of 
two cylinders^ one high pre^stire^ and the other low pressure. 
Each cylinder has its own connecting rod and cranky the 
cranks being set at opposite ends of the main engine shaft, 
and at an angle of 90° to each other. The two cylinders 
are connected by piping, and there is generally a receiver 
between them^ into which the high pressure cylinder ex- 
hausts, and is held in reserve until the opening of the low 
pressure admission valve. Figure 111 shows a cross com- 
pound engine, the receiver being underneath the floor. The 
power unit shown in figure 110 may be considered as con- 
sisting of two cross compound engines. 

Tandem Compound. In the tandem compound, the two 
cylinders are arranged tandem to each other, as shown in 
Figure 112. The advantage claimed for this type of com- 
pound engine is that it gives a much shorter and more 
direct route for the exhaust steam, in its passage from the 
high to the low pressure cylinders. 

Two Loio Pressure Cylinders. Where large units are 
required, it frequently happens that the low pressure cylin- 
der figures beyond the capacity of the station for handling 



366 



Steam Engineering 



the work. To meet this limitation^ two low pressure cylin- 
ders, each of one-half the total area, may be employed ; both 
cylinders being connected with one receiver, three cranks 
are employed, one in the center and one on each end of 
same shaft and keyed at 120 degrees to each other. 

Table 30 
numbers, their square roots and cube roots. 





d 
12; 


:3 


II 


i 


3 


II 


d 


s 




d 
!2; 




3.16 


10. 


2.15 


4.24 


18. 


2.62 


5.10 


26. 


2.96 


5.83 


34. 


3.24 


3.19 


10.2 


2.16 


4.26 


18.2 


2.63 


5.12 


26.2 


2.96 


5.84 


34.2 


3.24 


3.22 


10.4 


2.18 


4.28 


18.4 


2.64 


5.14 


26.4 


2.97 


5.86 


34.4 


3.25 


3.25 


10.6 


2.19 


4.30 


18.6 


2.64 


5.16 


26.6 


2.98 


5.87 


34.6 


3.26 


3.28 


10.8 


2.20 


4.33 


18.8 


2.65 


5.18 


26.8 


2.99 


5.89 


34.8 


3.26 


3.31 


11. 


2.22 


4.35 


19. 


2.66 


5.19 


27. 


3.00 


5.91 


35. 


3.27 


3.34 


11.2 


2.24 


4.38 


19.2 


2.67 


5.21 


27.2 


3.01 


5.92 


35.2 


3.27 


3.37 


11.4 


2.25 


4.40 


19.4 


2.68 


5.23 


27.4 


3.01 


5.94 


35.4 


3.28 


3.40 


11.6 


2.27 


4.43 


19.6 


2.69 


5.25 


27.6 


3.02 


5.96 


35.6 


3.28 


3.43 


11.8 


2.28 


4.45 


19.8 


2.70 


5.27 


27.8 


3.03 


5.98 


35.8 


3.29 


3.46 


12. 


2.29 


4.47 


20. 


2.71 


5.29 


28. 


3.03 


6.00 


36. 


3.30 


3.49 


12.2 


2.30 


4.50 


20.2 


2.72 


5.30 


28.2 


3.04 


6.01 


36.2 


3.30 


3.52 


12.4 


2.32 


4.52 


20.4 


2.72 


5.32 


28.4 


3.04 


6.03 


36.4 


3.31 


3.55 


12.6 


2.33 


4.54 


20.6 


2.73 


5.34 


28.6 


3.05 


6.04 


36.6 


3.32 


3.58 


12.8 


2.34 


4.56 


20.8 


2.74 


5.36 


28.8 


3.06 


6.06 


36.8 


3.32 


3.60 


13. 


2.35 


4.58 


21. 


2.75 


5.38 


29. 


3.07 


6.08 


37. 


3.33 


3.63 


13.2 


2.37 


4.60 


21.2 


2.76 


5.39 


29.2 


3.07 


6.09 


37.2 


3.33 


3.66 


13.4 


2.38 


4.63 


21.4 


2.77 


5.41 


29.4 


3.08 


6.11 


37.4 


3.34 


3.69 


13.6 


2.39 


4.65 


21.6 


2.78 


5.43 


29.6 


3.08 


6.12 


37.6 


3.34 


3.71 


13.8 


2.40 


4.67 


21.8 


2.79 


5.45 


•29.8 


3.09 


6.14 


37.8 


3.35 


3.74 


14. 


2.41 


4.69 


22. 


2.80 


5.47 


30. 


3.10 


6.16 


38. 


3.36 


3.76 


14.2 


2.4^ 


4.71 


22.2 


2.80 


5.49 


30.2 


3.10 


6.17 


38.2 


3.37 


3.79 


14.4 


2.43 


4.73 


22.4 


2.81 


5.50 


30.4 


3.11 


6.19 


38.4 


3.37 


3.82 


14.6 


2.44 


4.75 


22.6 


2.82 


5.52 


30.6 


3.12 


6.20 


38.6 


3.38 


3.85 


14.8 


2.45 


4.77 


22.8 


2.83 


5.54 


30.8 


3.13 


6.22 


38.8 


3.38 


3.87 


15. 


2.46 


4.79 


23. 


2.84 


5.56 


31. 


3.14 


6.24 


39. 


3.39 


3.90 


15.2 


2.48 


4.81 


23.2 


2.84 


5.58 


31.2 


3.14 


6.25 


39.2 


3.39 


3.92 


15.4 


2.49 


4.83 


23.4 


2.85 


5.60 


31.4 


3.15 


6.27 


39.4 


3.40 


3.95 


15.6 


2.50 


4.85 


23.6 


2.86 


5.61 


31.6 


3.16 


6.28 


39.6 


3.41 


3.98 


15.8 


2.51 


4.87 


23.8 


2.87 


5.63 


31.8 


3.17 


6.30 


39.8 


3.41 


4.00 


16. 


2.52 


4.89 


24. 


2.88 


5.65 


32. 


3.17 


6.32 


40. 


3.42 


4.03 


16.2 


2.53 


4.90 


24.2 


2.88 


5.67 


32.2 


3.18 


6.33 


40.2 


3.42 


4.05 


16.4 


2.54 


4.92 


24.4 


2.89 


5.68 


32.4 


3.18 


6.35 


40.4 


3.43 


4.08 


16.6 


2.55 


4.95 


24.6 


2.90 


5.70 


32.6 


3.19 


6.36 


40.6 


3.48 


4.10 


16.8 


2.56 


4.97 


24.8 


2.91 


5.72 


32.8 


3.19 


6.38 


40.8 


3.44 


4.12 


17. 


2.57 


5.00 


25. 


2.92 


5.74 


33. 


3.20 


6.40 


41. 


3.45 


4.14 


17.2 


2.58 


5.02 


25.2 


2.92 


5.76 


33.2 


3.20 


6.41 


41.2 


3.45 


4.17 


17.4 


2.59 


5.04 


25.4 


2.93 


5.77 


33.4 1 


3.21 


5.43 


41.4 


3.i6 


4.19 


17.6 


2.60 


5.06 


25.6 


2.94 


5.79 


33.6 1 


3.22 


6.45 1 


41.6 


3.46 


4.22 


17.8 


2.61 


5.08 


25.8 


2.95 


5.81 


33.8 1 


3.23 


6.46 1 


41.8 


3.47 



Triple Expansion Engine. In the triple expansion en- 
gine the steam is expanded successively in three cylinders. 



Compound Engines 



367 



each larger in diameter than its predecessor. There is first 
the high pressure cylinder^ second the intermediate cylin- 
der^ and third the low pressure cylinder^ from which the 
steam exhausts into the condenser. Very high initial pres- 
sure (200 to 225 pounds per square inch) is necessary with 
this type of engine^ as well as the quadruple expansion en- 
gine consisting of four cylinders^ in order to get good effi- 
ciency. The two latter types of multiple expansion en- 
gines^ viz., the triple and quadruple expansion are best 
adapted to pumping station work, rather than to the high 
speeds, and variable loads of the central power station. 
Owing to present day limitations on boiler pressure, the 
most desirable number of expansions in each cylinder of 
the different types of condensing engines should be 
about as given in Table 31. 

Table 31 
number of expansions. 







en 

C 


Expansions in Each Cylinder. 


TYPE 


1st. 


2nd. 


3rd. 


4th. 


Single expansions 


65 
145 
185 
265 


7 . 
22 
30 
48 


7. 

4.8 
3.2 
2.7 


4.6 
3.1 
2.65 


3.0 

2.6 




Double expansions 




Triple expansions . . '. 




Quadruple expansions 


2.55 



The Steam Jacket. Authorities differ as to the advan- 
tages derived from the steam jacket for the low pressure 
cylinder of a compound engine. There is no doubt that 
in the case of an engine furnishing power for shop pur- 
poses during working hours only, which implies that the 
service is not continuous, or rather that the engine is in 
service only ten or twelve hours out of twenty-four, the 
steam jacket is of great benefit in keeping the cylinder and 



3fi8 , Steam Engineering 

valve chest warm^ and thus preventing the severe strains 
which would result from the contraction and expansion^ of 
the metal. The weight of steam per indicated horse-power 
per hour that is condensed in the jaclcet varies from 1.7 
pounds to 3.8 pounds^ the average being about 2.3 pounds; 
while the economy of the thoroughly steam-jacketed cylin- 
der over the jacketless one varies from 3 pounds to as high 
as 7.9 pounds of steam per I. H. P. per hour^ or an average 
of about 4 pounds less steam consumed per H. P. H. by the 
use of the jacket^ after deducting the weight of steam con- 
sumed in the jacket. Judging from all the authorities 
whom the writer has been able to consult, and also from 
his own practical experience along this line, it seems plain 
that an actual saving of from 5 to 15 per cent in the con- 
sumption of steam can be effected by the judicious use of 
the steam jacket. In other words, if an engine with un- 
jacketed cylinders consumes steam at the rate of 20 pounds , 
per H. P. H. the same engine with its cylinders jacketed 
would develop the same amount of power with a consump- 
tion of only 16 pounds or 17 pounds per H. P. H. besides 
the advantage of having the cylinders always warm and 
ready for operation. 

QUESTIO^^S AND ANSWERS. 

295. Into what two general classes are steam engines 
divided. 

Ans, Simple and compound. 

296. Describe a simple engine. 

Ans, A simple engine may be either condensing or non- 
condensing, but its leading characteristic is, that the steam 
is used in but one cylinder. 

297. What is a condensing engine? 



Questions and Answers 369 

Ans. One in which the exhaust steam is passed into an 
air-tight vessel in which a vacunm is maintained^ the ex- 
haust steam being there condensed by coming in contact 
with cold water^ or a series of tubes through which cold 
water is being circulated. 

298. Describe a compound engine? 

Ans. A compound engine is one in which the steam is 
made to do work in two or more cylinders before it is al- 
lowed to exhaust. 

299. How is this accomplished.^ 

Ans. By causing the exhaust steam from the firsts or 
high pressure cylinder^ to pass into a second cylinder of 
larger diameter^ and, if the engine be triple or quadruple 
expansion, from thence into a third or fourth cylinder, 
the diameters of which increase in regular ratio. 

300. What is a non-condensing engine ? 

Ans. One from which the steam exhausts directly into 
the atmosphere, or is used for heating purposes before 
passing out into the open air. 

301. What disadvantage does a non-condensing engine 
constantly labor under? 

Ans. The pressure of the atmosphere amounting to 
14.7 pounds per square inch is constantly in resistance to 
the motion of the piston. 

302. , Mention several other causes that tend to increase 
the back pressure upon the piston of a non-condensing en- 
gine. 

Ans. The resistance of bends and turns in the exhaust 
pipe, also causing the exhaust to pass through feed water 
heaters or heating coils. 

304. What is back pressure? 

Ans. Pressure that tends to retard the forward stroke 
of the piston. 



370 Steam Engineering 

305. What advantage has a condensing engine over a 
non-condensing engine? 

Ans. The atmospheric pressure is removed from in front 
of the piston to a degree corresponding to the height of 
the vacuum that is maintained in the condenser. 

306. How many classes of condensers are there in gen- 
eral use? 

Ans. Two; jet condensers and surface condensers. 

307. Describe a jet condenser. 

Ans, One in which the steam is exhausted into an air- 
tight vessel, and is there condensed by coming in contact 
with a jet or spray of cold water. 

308. How is this water removed? 

Ans, By means of the air pump, which also maintains 
a vacuum in the condenser. 

309. Describe a surface condenser. 

Ans, It is an air-tight vessel, either cylindrical or 
rectangular in shape, fitted with a large number of brass 
or copper tubes, of small diameter, through which the cold 
water is forced by the circulating pump. A vacuum is 
maintained in the body of the condenser by the air pump, 
and the steam exhausted into this is condensed by coming 
in contact with the cool surface of the tubes. In some 
cases the steam passes through the tubes in place of around 
them, the condensing water being forced into and through 
the body of the condenser, and the vacuum being main- 
tained in the tubes. 

310. Describe an injector condenser. 

Ans, A condenser in which the cold water is forced 
through an annular enlargement of the exhaust pipe, and 
passing down into a nozzle which gradually contract?. The 



Questions and Ansiuers 371 

exhaust steam entering at the same time is condensed^ the 
water rushing through the nozzle with a velocity sufficient 
to create a vacuum. 

311. About what quantity of water is required per 
horse-power per hour to condense the exhaust steam from 
an engine ? 

Ans. About 38 to 40 gallons^ depending upon the tem- 
perature of the condensing water. 

312. What three factors are necessary to insure good 
economy with multiple cylinder engines? 

Ans. First — A high initial pressure. Second — Expan- 
sion of the steam to greatest extent possible. Third — Pro- 
tecting the surfaces of the cylinders from cooling influences. 

313. Describe a cross compound engine. 

Ans, An engine consisting of two cylinders^ each hav- 
ing its own connecting rod and cranky the cranks being 
set at opopsite ends of the engine shafts and at an angle 
of 90° to each other. The high pressure cylinder exhausts 
into the low pressure cylinder^ usually through a receiver. 

314. Describe a tandem compound engine. 

Ans. An engine having the two cylinders arranged tan- 
dem to each other^ with a common piston rod^ and connect- 
ing rod. 

315. What advantage is gained by this design? 

Ans. A much shorter and more direct route for the 
exhaust steam in its passage from the high to the low pres- 
sure cylinder. 



Valves and Valve Setting 

• It goes without saying that every man who aspires to be 
ai^ engineer should endeavor to thoroughly acquaint him- 
self with the principles governing the action of valves^ as 
well as the details of valve adjustment. But it must be 
remembered that this knowledge cannot be acquired in a 
day or a week^ or even months. True^ a man may be 
able to learn some of the alphabet of valve lore in a com 
paratively short time^ but the more practical experience 
he has in the work, the more will he realize the supreme 
need of mastering all the details of the process. 

The common D .slide valve, simple as it appears, is 
capable of furnishing problems over which savants have 
puzzled them^selves. 

The development of the full amount of power of which 
the engine is capable, its efficiency and economical use of 
steam, and its regular and quiet action are, in the largest 
degree, dependent upon the correct adjustment of its valve, 
or valves. 

There are many different types of valves for controlling 
the admission and release of steam to and from the cylin- 
ders of engines, but the basic principles governing the ad- 
justment of all, whether slide, poppet, rotative, piston, etc., 
are exemplified in the action of the common D slide valve, 
viz., the admission of the steam to J;he cylinder, its cut ofl 
and release, and the closure of the exhailst, each and all 
of which events are to take place at the proper moment 
during one stroke of the piston. 

373 



374 



Steam Engineering 



In order to properly perform tliese important functions 
the valve must have lead and lap. The various terms re- 
lating to valve action are plainly defined in the section on 
"^^Definitions/^ and it is unnecessary to repeat them here. 
If the outside lap is increased admission will be later and 
cut off earlier^ and if it be desired to keep the lead the 
same it will be necessary to move the eccentric forward^ 
which will make the other events^ cut off^ release and com- 
pression, earlier also. If the inside lap is increased the 
result will be an earlier closing of the exhaust and in- 
creased compression. 




These propositions refer mainly to engines of the single 
valve variety in which one valve controls the admission and 
distribution of the steam for both ends of the cylinder. 
In engines of the four-valve type, having a separate steam 
and exhaust valve for each end of the cylinder, each in- 
dividual valve may be adjusted independently of the others, 
as will be explained later on, and in the case of engines 
having separate eccentrics, one for the steam, and one for 
the exhaust valves, the adjustment becomes still more per- 
feet. 

We will first study the action of the D slide valve by 
referring to Fig. 116, which is a sectional view of a valve, 
valve sep.t and ports. The valve is represented at mid travel 



Valves and Valve Setting 375 

or in its central position. S. P^ S P are the steam ports, 
and E P is the exhaust port. The projections marked X 
at each foot of the arch inside the valve represent inside 
lap, and may be added to or taken from the inside edges of 
the valve^ according as more or less compression is desired. 
The dotted lines, L, L represent outside lap. 

Motion is imparted to the valve through the medium 
of the eccentric. If the valve had neither lap nor lead the 
position of the eccentric on the crank shaft would be just 
90°, or one-quarter of a circle, ahead of the crank, but as 
more or less lap as well as lead is required, it becomes 




Fig. 117 



necessary to move the eccentric still farther ahead of the 
crank, and this farther advance is termed angular advance, 
lap angle for lap, and lead angle for lead. 

Assuming the piston to be at the end of the stroke to- 
wards the crank, in other words, the engine to be on the 
dead center, the first function of the valve is lead or ad- 
mission, illustrated by Fig. 117. Owing to the valve hav- 
ing both lap and lead, the position of the highest point of 
the eccentric will be assumed in this case to be 120° ahead 
of the crank, the position of the latter being at'»0°. 

Exhaust opening has also occurred at the opposite end 
of the cylinder. The second function is full port opening, 
Fig. 118, the crank having moved through 60° and the 



376 Steam Engineering - 

eccentric is now at 180°, the farthest point of its throw 
in that direction, the valve being at the end of its travel. 
At this point it might be well to note a matter about which 
some persons are liable to become confused, simple as it is, 
viz., that the travel of a slide valve equals twice the port 
opening plus twice the outside lap. For instance, suppose 




the width of each steam port to be 1^/4 inches and the out- 
side lap to be 1 inch. In Fig. 118 the valve is at the ex- 
treme end of its travel towards the right and is about to 
return. It first covers port number one=:li4 inches. Next 
it moves to mid travel lap number one=2i4: inches. Its 
next move is lap number two=3i/4 inches, and lastly it 

-< — ^ 




Fig. 119 



uncovers port number two=4i/2 inches, which is its travel. 
To return to the third function of the valve or cut off. 
Fig. 119. The crank has now traversed 120°, and the high- 
est point of the eccentric is at 60° on the return circle, a 
point equivalent to 240^ of the circle described by the 
crank. 



Valves and Valve Setting 



377 



The fourth function is when compression begins at the 
head end of the cylinder^, Fig. 120. The crank is now at 
150°, the piston being near the end of the stroke and the 
eccentric has reached 90° of the return circle, or three- 
quarters of the crank circle, while the crank has still to 
travel 30° in order to complete the first one-half of its 




Fig. 120 



circle. At this point we can study the effect of inside lap, 
because if the valve has no inside lap, release on the crank 
end will begin almost at the same moment that compres- 
sion takes place at the head end, but by adding inside lap, 
compression can be caused to take place earlier and release 
later. 




Fig. 121 



The next event is admission at the head end of the 
cylinder, Fig. 121. The crank has now arrived at 180°, 
.having completed one-half of a revolution; the piston is 
at the end of the stroke, and the eccentric is at 120° on 
the return path. Fig. 122 serves to better illustrate the 
relative positions of the crank pin and eccentric during the 



378 



Steam Engineering 



stroke. The inner circle represents the path described by 
the high point of the eccentric, and the large circle that of 
the crank pin. The radius C 2 of the small circle represents 
the throw of the eccentric, and the distance C L is the lap 
of the valve plus the lead. The point of intersection of the 
Vertical line, L 1, with the eccentric circle locates the posi- 
tion of the highest point of the eccentric, and the line CB, 





AH 


/p" 




If 


\ 


^ 




A 


f \ 


^ 


\ \ / 



f%0' 



\h 



y^ 



^o. 



90' 

Fig. 122 



drawn from the center of the crank shaft through this point, 
indicates the angular advance which in this case is 30°, 
represented hy the angle ABC. The figures 1, 2, 3, 4, 5 
indicate the position of the high point of the eccentric at 
the moment of each function of the valve. The action 
of the valve can be more graphically illustrated by means' 
of valve diagrams, of which there are several different 
kinds, notably the Bilgram and Zeuner. The Zeuner dia- 
^^•am will be made use of in this instance. 



Valves and Valve Setting 



379 



Figure 123 shows the total movement of the valve, re- 
gardless of lap and lead. First draw line C 1 to represent 
the center line of the engine. Next draw line C 4 perpen- 
dicular to the line of centers, with C as the center of the 
crank shaft. The radius of the semi-circle D, 1, 2, 3, 4, 5, 




Fig. 123 

6 equals the radius of eccentricity. Line C D represents 
the position of the crank when the valve is at mid travel 
! or in its central position, D being the location of the crank 
pin. Eef erring back to Fig. 116, the valve is there shown 
in its central position, and supposed to be moving in the 
direction of the arrow in order to admit steam to the crank 



»^H0 steam Engineering 

end of the cylinder. Again referring to Fig. 123, draw line 
C A in such a position that the angle ABC will equal the 
angular advance of the eccentric, which we will assume in 
this case to be 30°. 

This will bring the high point of the eccentric at -B while 
the crank, as before stated, is at D. Next using line C A 
as the diameter, draw a circle about it called the valve 
circle. Now suppose the crank to be turning in the direc- 
tion of the arrows. At position D the crank line is just 
about to cut into the valve circle, the valve being central. 
When the crank gets to position 1 the valve has moved 
the distance C E. "When the crank is at 2 the valve has 
moved the distance C M, and when the crank arrives at 3 
the valve has moved to the limit of its travel from its cen- 
tral position, and it now begins the return movement. The 
motion of the valve is comparatively slow at this point 
for the reason that the high point of the eccentric is now 
passing the center at 7. The distance the valve has moved 
backward while the crank has moved from 3 to 4 is the 
distance B F, while F C represents its distance from the 
central position, and G C the same when the crank is at 5. 
When the crank arrives at 6 and its line has left the valve 
circle, the valve is again central. Figure 123 merely shows 
the movement of the valve through one-half of its travel 
without giving any details regarding port openings, cut 
off, etc. 

In Fig. 124 the influence of outside lap is delineated. 
According to the dimensions of the valve under considera- 
tion the outside lap is one inch. The diagram is drawn 
precisely as in Fig. 123, and in addition strike an arc 
representing the outside lap, using C as the center with a 
radius equal to the outside lap. As before, the crank is at 



Valves and Valve Setting 



381 



D and the valve central. When the crank has mored to E 
and its line cuts the intersection of the outside lap and 
valve circles^ the valve has moved the distance C H, just 
equal to the outside lap, and the port begins to uncover at 
.this point. Then by the time the crank gets to the center, 




(^^^S'^cct Cap =- / ^ 

Fig. 124 

1, the port IS open the distance L 0, which is the lead, in 
this case %-inch. This position of the valve is shown in 
Fig. 117. 

The position of the crank when cut off takes place is 
ascertained by drawing a line, C G 5, through the inter° 



:382 



Steam Engineering 



section of the outside lap and valve circles, where the valve 
is on its return movement (see Fig. 119). Thus far no 
account has been taken of release and compression, and in 
order to determine the position of the crank when these 
^events occur it will be necessary to draw the valve circle 





1 / / \ 




9 


£ 


10 




V2 J r"X 






V 







Fig. 125 

"for the opposite movement of the valve, for be it remem- 
bered that the movement of the valve so far considered has 
been only one-half of its travel; that is, it has moved from 
its central position towards the head end of the cylinder, 
and back again. We have seen how it has thus performed 
the functions of admission, full port opening and cut off 



Valves and Valve Setting 



383 



for the crank end of the cylinder, and now by referring 
to Fig. 125 it will be seen at what point of the stroke the 
remaining events, viz., release and compression, occur. 

Draw a second valve circle. Fig. 125, diametrically oppo- 
site the first. Also draw an arc with a radius equal to the 




Fig. 126 



inside lap, which in this case is assumed to be one-half inch. 
When the crank gets to the position 7 its center line cuts 
the intersection of the inside lap and valve circles, and 
release begins. When the crank arrives on the center 8,. 
the valve has moved the distance C T from central position ; 
but C X of this distance has been occupied by the inside 



384 



Steam Engineering 



lap^ therefore the lead on the exhanst is represented by the 
distance X T. When the crank on its return stroke arrives 
at the position marked 10^ its line again cnts the inter- 
section of the inside lap and valve circles and compression 
takes place, as in Fig. 120. By dropping perpendiculars 



C / 



N J^f 



A^ 



.y 



r/ 



R>-- 



Fig. 127 

from the positions of the crank at 1, 5, 7 and 10 an indi- 
cator diagram may be drawn showing the performance of 
an engine with this style of valve. 

Figure 126 shows the effect of decreasing the angular 
advance^, that is, setting the eccentric back towards the 



Valves and Valve Setting 385 

crank. . In this instance the eccentric is set bacK 10°^ thus 
making the angle of abvance 20° instead of 30°^ as before. 
The full lines represent the new angle, while the dotted 
circles and lines indicate the valve and its movements as 
drawn at first. A shows the original point of admission 
and A' the position of the crank when admission takes place 
with the lesser angle of advance. Similarly, E and E^ show 
the old and new points of release, and C and C^ the com- 
pression. The two different points of cut off are al&o in- 
dicated. It will be observed that all of these events occur 
later and the lead also is diminished. 

In locomotives, and also in some types of adjustable cut 
off engines, the travel of the valve may be varied at will, 
and the effect of decreasing the valve's travel is illustrated 
by Fig. 127, the full lines showing the decreased travel and 
its influence, and the dotted lines showing the original. 
Admission and release occur later, while cut off and com- 
pression take place earlier, and the lead is less. The travel 
of the valve as indicated in Fig. 127 has been decreased 
one inch, making it 3% inches in place of 4% inches as 
before. 

Figure 128 shows the result of increasing the outside 
lap. The lap has been increased in this case from 1 inch, 
as originally drawn, to I14 inches, as indicated by the full 
lines, while the dotted lines show the lap as it was before 
being changed. The effect of this change is to cause less 
lead, a later admission and an earlier cut off, but compres- 
sion and release are not aJffected for the reason that these 
latter events are controlled by the inside lap, which has 
not been changed. 

In Fig. 125 the valve is shown as cutting off the steam 
when the crank has completed 120°, or two-thirds of the 



386 



Steam Engineering 



half revolution, but the point of cut off on the indicator 
■ diagram shows tliat the piston has traveled 7/9 of the 
stroke. This discrepancy is due to the obliquity of the 
connecting rod, as it will be seen by looking at the valve 
diagram. Fig. 125, that the crank must travel farther to 




Fig. 328 



complete the stroke from this point than the piston does. 
In order to cause the valve to cut off earlier, say at one- 
half stroke, it will be necessary to do one of two things, 
either to increase the outside lap, which would have a 
tendency to cause admission to occur too late, or the angle 
of advance may be increased sufficient to cause cut off to 



Valves and Valve Setting 



387 



take place at half stroke, but to do this alone would cause 
admission to occur too early. Therefore the proper thing 
to do is to increase both the angle of advance and the 
outside lap. Figure 129 shows how this can be done with- 
out decreasing the travel of the valve. The angle of ad- 




Fig. 129 



°, where before it was 30°, as in 



vance, A B C, is now 50 
Fig. 125. 

The valve is central when the crank is at position 1 ; 
the high point of the eccentric being at point 4. The out- 
side lap, which before was 1 in., has had 7/16 in. added 



388 Steam Engineering 

to it, making it 1 7/16 in. When the crank gets to D the 
port is just commencing to open^ and with the crank on 
the center at 2^ the lead is 14 i^- 

It will readily be seen at this point that by increasing 
the outside lap still more the lead can be diminished^ and 
the pjoint of cut off made still earlier^ but this would result 
in a still further reduction of the power of the engine, 
which has already been considerably reduced, as shown by 
the diminished area of the indicator diagram as compared 
with the one in Fig. 125. When the crank gets to position 
3 the valve has reached the limit of its travel, and the port 




Fig. 130 

is open the distance A a, which is as far as the outside lap 
will permit. With the crank at point 4 cut off occurs. 
But with the increased angular advance and the inside 
lap remaining as it was before, viz., V2 i^-.^ release would 
occur too early. Therefore it will be necessary to increase 
the inside lap sufficient to cause release and compression to 
take place at as near the proper points as possible. In this 
instance % in. has been added, making the inside lap % 
in., and release takes place with the crank at position 5, 
while compression begins at 6. These points may also be 
changed by simply adding to, or decreasing the inside lap. 
It should be noted that in the foregoing discussion of 
valve gear it is understood that the valve stem moves in 




Valves and Valve Setting 389 

^the same direction as the eccentric rod^ that is^ the direc- 
tion of motion is not reversed by a rocker arm interposed 
between the eccentric and the valve. 

The first step in the operation of valve setting is to place 
the engine on the dead center^ which means that the piston 
is at the end of the stroke^ and the centers of the main 
shafts crank pin and crosshead pin^ or wrist pin^ as it is 
sometimes called^ are in line (see Fig. 130). When mov- 
ing the engine to place it on the center it should always 
be turned in the direction in which it is to run. This is 
to guard against any errors which might result from lost 




Fig. 131 

motion or looseness m the reciprocating parts. Turn the 
fly wheel around until the crosshead is almost to the end 
of the stroke^ say within a half inch of it^ as at Fig. 131. 
Then with a steel scriber or penknife mark the location 
of the crosshead on the guides A^ also provide a secure rest- 
ing place upon the floor of the engine-room for a marker 
to be placed against the rim of the wheel. This rest should 
be firmly fastened to the floor in order that its position 
may not be changed during the operation of valve setting. 
Place the marker against the wheels as at B^ and mark the 
point with a center punch or cold chisel. Next turn the 
engine carefuly until the crosshead completes the stroke 
and moves back on the return stroke until the mark A is 



390 Steam Engineering 

in line again. Make another mark on the rim of the wheel 
opposite the marker at C. This position of the engine is 
shown in Pig. 132, and it will be seen that the crank is 
now as much above the center as it was below in Fig. 131. 
Now with a pair of large dividers ascertain the middle or 
half distance between marks B and C and put another mark 
D, at this point. Then turn the engine a complete revolu- 
tion until mark D comes opposite the pointer, Fig. 130, 
and the engine will be on the true center. 

At this point the question may arise, why not simply 
reverse the motion and back the wheel up until the mark 




Fig. 132 

D is in line with the marker? The answer is, that while 
• this would undoubtedly save considerable labor, yet it 
would almost certainly result in an error, on account of the 
lost motion of the moving parts, which would permit of 
•considerable movement of the wheel before any movement 
of the crosshead would take place if the wheel was turned 
hack. The result would be that when mark D came to 
l3e opposite to the pointer, the crank would not be on the 
true center. The next move is to see that the eccentric 
rod is adjusted to the proper length. If there is a rocker 
arm, connect the eccentric rod in its proper place, leaving 
the valve rod disconnected for the time being. Then ad- 
just the length of the rod so that when the eccentric is 



Valves and Valve Setting 



391 



turned around on the shaft the rocker arm will vibrate 
equal distances on each side of a plummet line suspended 
through the center of the pin upon which the arm turns, 
as in Fig. 133. Before connecting the valve rod the valve 






£ece;ti/itc /&<^ 









Fig. 133 

should be put in its central position and marked. To do 
this it will be necessary to first ascertain the outside lap. 

The most accurate method of doing this is to take the 
valve out and measure the distances between the outside 
edges of the steam ports, as at B, Fig. 134. Then measure 
the width of the valve from edge to edge, as at A. Then 



392 



Steam Engineering 



A — B-^2=the outside lap. For instance^ A=8.5 in., B= 
Q.^ in. Then 8.5—6.5=2, and 2 divided by 2=1 in., 
which is the lap. The inside lap should also be measured 
at this point for convenience, and the measurements pre- 
served for future reference. The inside lap is ascertained 
by measuring the distance between the inside edges of the 
ports and the distance across the arch of the valve from one 
inside edge to the other (see Fig. 134) and dividing the 




difference by 2. 
E is 3 in. ; then 



Fig. 134 

For instance, the distance F is 4 in., and ! 

3 

:.5 in., making the inside lap ^/2 in. 



2 



To place the valve central, measure the width of the 
outside lap each way from the outside edges of the steam 
ports and mark the points on the valve seat with a sharp 
lead pencil. Then place the valve with edges on the marks 
and it will be central. To insure accuracy, measurements 
should also be taken from the outside edges of the steam 
ports to the ends of the seats. Having fixed the valve in 



Valves and Valve Setting 393 

its central position^ replace the stem and if it is secured in 
the valve by nuts^ as in Fig. 134^ care should be taken to 
leave a little play for the valve between the nnts^ otherwise 
it is liable to become stuck, and held off the seat when it 
gets hot and expands. Make a center punch mark C, on 
the edge of the valve chest directly over the valve stem, 
and placing one leg of a tram or pair of dividers in the 
mark, with the other leg describe a mark on the top of 
the valve as at D, thus marking the valve in its central 
position. 

Now with the rocker arm perpendicular, the eccentric 
rod having been previously adjusted, connect the valve rod 
to the rocker, and turn the eccentric to the limit of its 
throw in one direction, and measure the distance the valve 
has traveled from its central position. Then turn the ec- 
centric around to its extreme throw in the other direction, 
and if the valve travels the same distance from its central 
position in the opposite direction the lengths of the rods 
are correct, but if not correct, the necessary change can 
usually be made by shifting the nuts on the valve stem, 
or if the valve is secured to the stem by a yoke the change 
can be made in the rod. 

Having succeeded in getting- the correct travel for the 
valve, the next step is to set the eccentric. With the 
engine on the dead center, turn the eccentric around on 
the shaft in the direction in which the engine is to run, 
so as to take up all the play in the valve stem and other 
moving parts, and with the tram, or dividers watch the 
valve until it has moved away from its central position by 
the amount of its outside lap, plus the lead it is desired 
to give the valve. For instance, if the valve has one inch 
outside lap and the lead is to be % in., the valve should be 



394 Steam Engineering 

moved away from its central position 1% in., and also 
away from the end of the cylinder at which the piston is. 
The steam port for that end should now be open % in., 
and the eccentric should be ahead of the crank one-qnarter 
turn plus the angular advance required for the outside 
lap and lead, or if as previously explained, the motion of 
the eccentric is reversed by a rocker arm the eccentric 
should be behind the crank by the same amount. Tighten 
the set screws holding the eccentric on to the shaft and 
turn the engine around until it is on the opposite center. 
Then if the lead is the same on each center the valve is set 
correctly. If the lead is not the same, move the valve on 
the stem toward the end having the most lead, a distance 
equal to one-half the difference between the two leads. If 
the lead as equalized is more than is desired move the 
eccentric back on the shaft until the correct lead opening 
is secured, then tighten the set screws permanently, and 
with a sharp cold chisel make a plain mark on the shaft, 
and opposite to this another mark on the eccentric. This 
will save considerable trouble in case the eccentric should 
slip or be accidentally moved from its true position at any 
time. 

Although the common D slide valve as applied to sta- 
tionary engines usually has its point of cut off fixed, yet 
there are many types of variable automatic cut off engines 
with single slide valves of various patterns, such as box 
valves in which the steam passes through the valve, piston 
valves, in which the steam either passes through or around 
the ends of the valve, so-called gridiron valves, and various 
other types. Such valves are generally applied to high speed 
engines, and are actuated by eccentrics which are under the 
control of shaft governors which vary the position of the 



Valves and Valve Setting 



395 



eccentric with relation to the crank according to the load 
that is on the engine, thus regulating the point of cut off 
so as to maintain a constant speed, while the throttle is 
kept wide open. While the details of setting all the var- 
ious styles of valves, including the Corliss or four-valve 
type, differ considerably from those required in setting the 
D valve, yet the same principles govern the operation, no 
matter what kind of a valve is to be adjusted. 




Fig. 135 



In all types of reciprocating engines the same factors 
affecting the distribution of the steam are present, viz., the 
outside or steam lap affecting admission and cut off, and 
the inside or exhaust lap affecting release and compression. 
While the D valve (and other types of single valves) com- 
bines these four principal factors within itself (that is, 
two steam laps and two exhaust laps), it should be noted 
that in the four-valve type of engine the same factors are 
distributed among four valves, each valve performing its 
own particular function in controlling the distribution of 
the steam for the end of the cylinder to which it is at- 
tached. Also each valve may be adjusted to a certain de- 



396 Steam Engineering 

gree independently of the others^ and this fact goes far 
towards explaining why engines of this type, with the dis- 
engaging valve gear, are so much more economical in the 
use of steam than are those with the ordinary fixed cut off. 
Thus, for instance, the steam valves of a Corliss engine 
may be adjusted to cut of! the steam at any point, from 
the very beginning up to one-half of the stroke, without in 
the least affecting the release or compression, because these 
events are controlled by the exhaust valves. 

In some of the modern improved makes of four-valve 
engines there are two eccentrics, one for the steam and the 
other for the exhaust valves. This arrangement permits 
of still greater latitude in adjustments for the economical 
use of steam. 

As the Corliss engine is a prominent and familiar type 
of the four valve detaching cut off engine, and embodies 
the main features of nearly all engines belonging to that 
class, it will be used to illustrate the method of setting 
the valves on a four valve engine. 

Fig. 135 is a sectional view of the cylinder, steam and 
exhaust chests, and the valve chambers of a Corliss engine. 
1 and 2 are the steam valves, and 3 and 4 the exhaust valves. 
The valves work in cylindrical chambers accurately bored 
out, the face of the valve being turned off to fit steam 
tight. They are what is termed rotative valves, that is, 
they receive a semi-rotary motion from the wrist plate, 
which in turn is actuated by the eccentric. 

In Fig. 135 the piston is shown as just ready to begin 
the stroke towards the left. Admission is taking place at 
valve 2 and release at valve 3, valves 1 and 4 being closed. 
The arrows show the direction in which the valves move. 
Motion is transmitted from the wrist plate to the valves by 



Valves and Valve Setting 



397 



means of short connecting rods and cranks attached to the 
valve stems. These rods are^ or at least should be, fitted 
with right and left hand threads or turn buckles for the 
purpose of lengthening or shortening the rods while set- 
ting the valves. 

The valve gear of a Corliss engine with a single eccentric 
is shown in Fig. 136. The connections of the exhaust 
valves with the wrist plate are positive^ and the travel of 
these valves is fixed, being a constant quantity, but the con- 



ff 












9 


^=? 




(J 


'A 


f/A 


^ 




(f*""^ 


^ 


^ 


t__ _ 


B 

■ 1 


[V 


( ® ) 


1 


c 




^ 


2 




v- 


? 




^ 




if% 


Fm 



Fig. 136 



nections of the steam valves with the wrist plate are de- 
tachable, being under the control of the governor. Various 
designs of releasing mechanism are in use by different 
builders, but the same general principles govern the oper- 
ation of all, viZc, that the valve is quickly opened at the 
commencement of the stroke when the wrist plate has its 
fastest motion, and that the governor trips the releasing 
mechanism at that point in the stroke at which it is de- 
sired that cut off should take place, and that the valve is 
then quickly closed by means of a vacuum dash pot or, as 



398 



Steam Engineering 



in some types of engines^ by a spring. Connection is made 
between the wrist plate and rocker arm by means of the 
hook rod, so-called because it hooks over the wrist plate pin, 
and can easily be disconnected in case it is desired to work 
the valves by hand, as in warming up the engine prepar- 
atory to starting up. 







Fig. 137 

Eef erring to Fig. 136, A is the wrist plate, B and C are 
the dash pot rods, D, D' the dash pots and H K the hook 
rod. G and G' represent the governor rods, and the figures 
1, 2, 3 and 4 indicate the valve rods with turn buckles for 
changing their lengths. 



Valves and Valve Setting 399 

As in setting the slide valve, the first requisite in setting 
Corliss valves is to put the engine on the center, the method 
of doing which has been fully described. Next adjust the 
length of the hook rod, if it is adjustable, if not, then the 
eccentric rod so that the wrist plate will vibrate equal dis- 
tances each way from its central position which is marked 
on top of the hub. (See Fig. 137.) It will be noticed 
that there are four marks. A, B, C and D. Marks A and 
"B are on the hub of the wrist plate and the stationary 
flange against which it turns, and when they are in line, 
indicate that the wrist plate is central. Marks C and D 
are on the stationary flange at equal distances each way 
from B, and when the engine is running mark A should 
travel to the right until it is in line with D and to the left 
until in line with C, or it may happen that A will travel 
past C and D or perhaps not quite to them, but which 
ever it does, it should stop at equal distances from them. 
This adjustment should be carefully made before setting 
the valves, because if any change is made in the lengths 
of the eccentric rod or hook rod after the valves are once 
set it will seriously affect the action of all the valves. 

The method of adjusting the rocker arm so that it will 
vibrate correctly has been already described and it is very 
desirable that its travel should be equidistant in either di- 
rection from a vertical position, but if it is found that the 
hook rod is non-adjustable as to length and that the wrist 
plate still vibrates too far in one direction, then the adjust- 
ment must be made on the length of the eccentric rod, 
which can be screwed into or out of the strap. The vibra- 
tion of the wrist plate should then be tested by turning 
the eccentric around on the shaft in the direction the engine 
is to run. When this is found to be correct the next step 



400 



Steam Engineering 



is to remove the back bonnets from the valve chambers. 
Fig. 138 represents one of the steam valves and Fig. 139 
one of the exhaust valves^ each with back bonnet removed, 
showing the ends of the valves. 




Fig. 138 



The working edges of the valve^ as well as the ports of 
a Corliss engine^ cannot be seen when the valves are in place, 
owing to the fact that the circular ends of the valves fill 
the spaces at the ends of the valve chambers, but certain 



^^ ^ 


> 1 


1 T-Z ^ 




/ \ 


^=\ 



Fig. 139 



marks will be found on the ends of the valves, and cor- 
responding marks on the faces of the chambers which serve 
as a guide in setting the valves. Eeferring to Fig. 138, 
mark V on the end of the valve is in line with the edge of 



Valves and Valve Setting 401 

the valve^ and P indicates the edge of the port. The same 
letters apply to Pig. 139. Having removed the bonnets 
and found the marks^ temporarily secure the wrist plate 
in its central position by tightening one of the set screws 
on the eccentric. Then connect the valve rods^ adjusting 
their lengths so that the steam valve will have from ^ to 
9/16 in. lap^ as in Pig. 138^ and the exhaust valves from 
3^2 to -^Q in. opening, as in Pig. 139. These figures 
vary according to the size of the engine, the smaller figures 
being for small size engines, and the larger figures apply 
to large sizes. 

In adjusting the steam valves be sure and note the direc- 
tion in which they turn to open. In most Corliss engines 
the arm of the crank to which the valve rod is connected 
extends downwards from the valve stem, as in Pig. 136. 
This will cause the valve to move towards the wrist plate 
in opening. After the valve rods have been properly ad- 
justed as to length, place the engine on either center by 
the method previously explained, and move the eccentric 
around on the shaft in the direction in which the engine 
is to run until it is far enough ahead of the crank to allow 
the steam valve the proper amount of lead opening, which 
will vary according to the size of the engine. - Table 32 
gives the lap and lead for various sizes of Corliss engines 
from 12 to 40 in. bore. Having tightened the eccentric 
set screws, turn the engine around to the opposite center 
and note whether the lead is the same on each end. If 
there is a difference it can generally be equalized by slightly 
altering the length of one of the valve rods. The valves 
should also be adjusted by means of the indicator at the 
first opportunity, as that is the only absolutely correct 
method. 



402 



Steam Engineering 
Table 32 



Size of Engine 



Lap of Steam 
Valve 



Lead Opening of 
Steam Valve 



i^ inch 

B2 inch 

iV inch 

iV inch 

1% inch 

tV inch 

i^ inch 

g\ inch 

5^5 inch 

5^ inch 

5^ inch 

§ inch 

§ inch 

g inch 

I inch 

§ inch 



Lead Opening of 
Exhaust Valve 



12 inches 


I 


inch 


14 inches 


1% 


inch 


16 inches 


t\ 


inch 


18 inches 


i 


inch 


20 inches 




inch 


22 inches 


1 


inch 


24 inches 


tV 


inch 


26 inches 


JL. 


inch 


28 inches 


JL 


inch 


30 inches 


h 


inch 


32 inches 


h 


inch 


34 inches 


I 


inch 


36 inches 


i 


inch 


38 inches 


T^F 


inch 


40 inches 


T% 


inch 


42 inches 


T% 


inch 



sV inch 

5^2 inch 

5^2 inch 

tV inch 

tV inch 

tV inch 

i^ inch 

g\ inch 

5^ inch 

g inch 

§ inch 

g inch 

i inch 

T% inch 

f^ inch 

T^g inch 



The next point to receive attention is the adjustment of 
the lengths of the horizontal rods extending from the 
governor to the releasing mechanism^ so that the steam 
valves will cut off at equal points in the stroke. This is 
done by raising the hook rod clear of the wrist plate pin, 
and with the bar provided for the purpose move the wrist 
plate to either one of its extreme positions as shown by the 
marks on the hub (see Fig. 137) and holding it in this 
position adjust the length of the governor rod for the steam 
valve (which will then be wide open) so that the boss or 
roller which trips the releasing mechanism is just in con- 
tact, or within 1/32 in. of it. Then move the wrist plate 
to the other extreme of its travel and adjust the length of 
the other rod in the same manner. To prove the accuracy 
of the adjustment, raise the governor balls to their medium 
position, or about where they would be when the engine is 
running at its normal speed and block them there. Then 
having again connected the hook rod to the wrist plate, 
turn the engine around in the direction in which it is to 
run, and when the valve is released, measure the distance 



Valves and Valve Setting 



403 



upon the guide that the crosshead has traveled from the.^ 
end of the stroke. Now continue to turn the engine in the 
same direction until the other valve is released, and 
measure the distance that the crosshead has traveled from 
the opposite end of the stroke, and if the cut off is equalized 
these two distances, will be the same. If there is a dif- 
ference, lengthen one rod and shorten the other until the 
point of cut oflE is the same for both ends. 




Fig. 140 



The lengths of the dash pot rods should also be adjusted 
so that when the plunger is at the bottom of the dash pot 
the valve lever will engage the hook. 

After all adjustments have been made, tighten the lock 
nuts on all the rods. 

Fig. 140 shows the wrist plate of a Eeynolds Corliss 
engine in its central position read)^ for adjusting valve 
connections. The parts broken away show the steam and 
exhaust valves in their respective positions as regards lap. 
The valves shown are single ported. 



40i 



Steam Engineering 



Fig. 141 shows the position of the wrist plate of a Rey- 
nolds Corliss engine^ when the crank is on the center and 
the eccentric set so as to give the steam valves the proper 




Fig. 141 



amount of lead. The exhanst valves wdll be correct if they 
have been set according to table 32 — the wrist plate being 
central. 




Pig. 142 shows the wrist plate of a heavy duty or re- 
liance type Eeynolds Corliss engine in its central position, 



Valves and Valve Setting 405 

ready for adjusting the lengths of the valve rods. The 
valves in this type of engines are double ported. 

Fig. 143 shows the position of the wrist plate of a heavy 
duty or reliance type Eeynolds Corliss engine^ when the 
crank is on the center, and the eccentric set so as to give 
the steam valves the correct lead. These valves are double 
ported, and the exhaust valves will be correct if set ac- 
cording to table 32. 




Fig. 143 



Reynolds Long Range Cut Off. Fig. 144 shows the 
valve gear side of an Allis- Chalmers engine equipped with 
the long range cut off which is designed to give a maximum 
cut-off for power, and the essential feature of the steam 
valves is, that they have a negative lap or opening when in 
mid-position, the cut-off being made entirely by the gov- 
ernor through the knock-off cam. 

Eeferring to Fig. 145, the steam and exhaust valves on 
one end of the cylinder are shown with the valve-gear re- 
moved and the valves and ports in cross-section, while on 
the other end the valve-cranks have been left in place, and 







Fig. 144 

VALVE-GEAR SIDE OF REYNOLDS LONG-RANGE CUT-OFF ENGINE 



Valves and Valve Setting 407 

show their relative position to the valves at the opposite 
end. The steam and exhaust wrist-plates are shown at A 
and B, respectively^ and above A is shown the travel circle 
C of the steam eccentric; below is the exhaust circle D. 
In these circles the crank position is at c and e is the ec- 
centric position. The steam valve-crank is indicated by 
E, the exhaust valve-crank by F; G is the bell-crank and 
H the knock-off cam. On the other end of the cylinder 
where the valves and ports are in cross-section, the dotted 
lines E', F', G' and H^ denote the center lines of the same 
parts on that end, and the arcs at the ends of these lines 
fihow the respective positions of the pin centers. From each 
end of these arcs the center lines show the positions of the 
pins when they reach their respective extremes of travel. 

In Fig. 145 the wrist-plates and all connected parts are 
shown in their central positions, at which the exhaust 
valves are lapped, as is usual in practice, but the steam 
valves are open on both ends when they are hooked up. If 
hooked up and not released the steam valves would be open 
from the beginning of one stroke up to 75 per cent of the 
return stroke, but when the knock-off cam-pin center is at 
a, the cut-off will be carried out to about seven-eights or 
eleven-twelfths of the stroke, and the cut-off will occur 
just before the steam valve on the opposite end picks up for 
lead. When the knock-off cams are in the position repre- 
sented by the lines H and H', Fig. 145, the cut-off will 
occur at about three-eights of the stroke, and when the 
knock-off pin center is at b the valves will remain lapped, 
being dropped before they can open. If the regulator is 
allowed to drop down so the knock-off cam-pin will reach 
the point c, the valves will not pick up and will remain 
lapped. This peculiarity must be thoroughly fixed in 
mind. 



408 



Steam Engineering 




Fig. 145 



In Fig. 146 the valve-cranks are in their extreme posi- 
tions, and the eccentrics likewise, with everything ready to 
start in the direction of the arrows. On the crank end the 
steam valve is lapped, and the exhaust valve is open, while 



Valves and Valve Setting 



409 




Fig. 146 



reverse conditions exist on the head end. On all other 
types of valve-gear the eccentrics would be advanced 90 
degrees when the valves are lapped^ but on this engine the 
steam valve is lapped when the eccentric is on its extreme 



410 Steam Engineering 

position. The exhanst valves are the same as on. any other 
double-eccentric Corliss engine. 

Setting the Valves, Bearing these points in mind we 
may proceed to set the valves. The amounts of lap and 
lead and the positions of the cranks from the center lines 
given herewith are for engine cylinders of 36, 42, 48, and 
60-inch stroke. 

First set the wrist-plates central and clamp them in 
place ; then adjust the lengths of the rods so that the steam 
valves are open ^^ inch, as shown in Fig. 145, and the 
exhaust valves are lapped -^q inch. If the rod lengths 
are right the center lines of the cranks E and E' will coin- 
cide, the pins of the cranks F and F' will be one-half inch 
from the center line, as shown, and the pins on each end 
of the bell-cranks G and G' will be 2% inches and -f^ 
inch from the center lines. When the valves have been 
set with the wrist-plates central, release the wrist-plates 
and roll the eccentrics around the shaft to test them, and 
the reach-rods, and see that they are of the right length 
to make the wrist-plate travel equally each side of the 
center line. 

Then place the crank on center, and pull the steam ec- 
centric around enough to give 3^2-iiich lead, and make it 
fast. Next mot^e the engine around in its direction of 
travel to about 95 degrees of its stroke, and move the ex- 
haust eccentric around until the exhaust valve on the same 
end is just opening or releasing. Make the exhaust ec- 
centric fast, and move the engine around its full revolu- 
tion and check ofi the valves on the other end, and the ex- 
haust closure. Then set the regulator up to its central 
position and adjust the lengths of the rods from the lever 
to the knock-off cams, so that the pins of the cams H and 



Valves and Valve Setting 



411 



H' will set % inch of the center line^ as in Fig. 145. 
Let the regulator down and hook up the wrist-plates; then 
pull the engine around to make sure that the steam valves 
are released on each stroke alternately, at not later than 
eleven-twelfths of the stroke, and always before the other 
valve picks up. 



:■,.:..■■■:. ■■;-v..;;-::■■■•;:w—r^■;:■ '^:^'i-:r:S::y--'--^:^- 


•■V. 


'^ffl^^^fl 


1- 


"^^Bi^^^^BBmJK 


m' 


~'aHH|^^p9HH 


1 


'^^^^^^^^S 


R? 


^^^^^BHI^Hh 


i '" 


'"-i^m^Bfl^m 


1 


^w 


1 




^^^^^k 




'^SHHp '^^^h 


1 


•^^«^^l 


1 



Fig. 147 

The Greene Wheelock Engine, In this engine, each 
cylinder is equipped with four valves of the Hill gridiron 
type, two steam and two exhaust to each cylinder, and each 
valve is driven by a separate eccentric. This type of valve 
and gear gives a large port opening, with a minimum of 
travel, which in connection with the Greene cut off on the 
steam, and the toggle motion on the exhaust valves, gives 



412 



Steam Engineering 



the quickest action at the right time to both. A minimum 
lap is also obtained with the aid of the gear. It is there- 
fore very important that the movements of the valve and 
gear be thoroughly understood^ and great care be used in 
adjusting it. The valve plugs contain the valve seats as 
an integral part of the plug. These are in turn remov- 
able for repairs^ as are also the valves when in position. 




Fig. 148 

To the plug is attached the head that holds the working 
parts of the valve mechanism. 

The arrangement of the valves beneath the cylinder as 
in the Wheelock system^, allows short ports, small clearance 
volume, and a free discharge for the water of condensation 
through the exhaust. The throttle also is beneath, and ad- 
mits steam to the steam chest under the cylinder. There 
are four eccentrics, one for each valve. These eccentrics 



Valves and Valve Setting 413 

are of small size and short tlirow^ and receive their motion 
from the eccentric shaft extending from the back cylinder 
head;, alongside the engine frame to the main crank shaft, 
from which it receives rotary motion through bevel gear. 

An understanding of the valve plugs and their location 
may be had by reference to Figs. 147, 148, 149. Fig. 147 
shows a longitudinal section of the cylinder, and the cross- 
section of the valve plug at A. This view gives the loca- 
tion of the inlet (steam) valve and seat at a and the out- 
let (exhaust) valve and seat at b, the steam chest B B 
forming a jacket for part of the cylinder, as well as admit- 
ting the steam through the inlet a into the cylinder. From 
the cylinder the steam passes out through the outlet b into 
the exhaust passage C. 

Fig. 148 is a cross-section of the cylinder through the 
clearance space and a longitudinal of the valve plug in that 
end of the cylinder, showing the back of the inlet valve seat, 
with the outlet valve cut away. 

Fig. 149 is a view of the valve plug with all of the parts 
assembled. This view shows the inlet or steam valve 
side of the plug. The inlet valve is at a ; the spring which 
holds it to its seat when not under steam pressure is at b ; 
and c is the pusher crank which actuates the valve by means 
of a cam at d, which comes in contact with the latch of the 
valve-stem head e. This is fastened to the inlet valve- 
stem by clamp bolts. The inlet valve-stem screws into the 
nut f, so that by loosening the clamp bolts of the head e 
and turning the rod, an adjustment of the valve setting 
can be made, as will be shown later. 

The inlet valve is opened by the pusher cam pushing 
it forward, but is released from this cam through the 
means of a trip cam on the bottom of the valve-plug head.. 



414 



Steam Engineering 




Fig. 149 

which is connected to the governor-rods. When released 
by the trip cam^ the valve cuts off by means of the steam 
pressure on the valve-stem controlled by a dash-pot ar- 
rangement in the valve-plug head to which the other end 
of the rod is attached. 



Valves and Valve Setting 415 

The outlet valve is inside of the valve ping nnder the 
stmt g. The position of this valve in relation to the inlet 
can be noted by reference to Fig. 147^ where the cross-sec- 
tion of the valves and seats is shown. The ontlet valve is 
actuated by the eccentric acting on the toggle joint h^ con- 
nected between the two pairs of links, from the point i, 
where it is fixed^ and the joint j, where the link is fastened 
to the valve-rod head k on the outlet valve-stem. 

Instructions For Proper Setting, The following in- 
structions are from the builders of these engines^ and if 
adhered to will give proper setting of the valves. The pre- 
vious illustrations will aid^ to a full understanding of these 
operations. 

For reference and a means of checking off the action of 
the valves it is stated that ^^A-size^^ valves have /2-i^ch 
lap, with %-inch travel, and are generally used on cylin- 
ders up to and including 16 inches in diameter; "B-size^^ 
valves have -x^g-inch lap, with 1 %-inch travel, and are 
generally used on cylinders from 18 to 26 inches in di- 
ameter, inclusive; "C-size^^ valves have i/4-inch lap, with 
1%-inch travel, and are used on cylinders from 28 inches 
in diameter upward. 

When starting to adjust the valves, first have all ec- 
centrics loose on the cylinder shaft, and, second, determine 
the direction the cylindei* shaft is to run, and always rotate 
the eccentrics in the same direction, whether loose on the 
shaft, or when the shaft and eccentrics turn together. 

To Adjust the Travel of the Steam Valves. On the 
edge of the pusher crank a line is made in the shop, and 
on the side of the plug head, next to the pusher crank, a 
corresponding line is made (where the arrow points). 
When the line on the pusher crank corresponds exactly 



416 Steam Engineering 

with the line on the side of the plug head, the pusher plate 
is vertical: This is its most backward position. 

Adjust the eccentric-rod for this valve to such a lenp-th 

o 

that in turning the eccentric around on the shaft the line 
on the edge of the pusher crank comes back to correspond 
exactly with the line on the plug head at each revolution. 
Then, by shimming, adjust the bridge-supporting trip cam, 
so that the steam valve will travel % of an inch on ''A- 
size,'' li/s inches on ^'B-size,'' and 1% inches on ^'C-size,'' 
but bear in mind that the valve must trip at the end of its 
travel and the bridge must not be so low that the valve 
will carry the full stroke without tripping. The roller 
of the lifter must be in position for full travel. 

To Set the Steam Valves. On the steam valve-stem, four 
scratch lines are made. These lines represent the valve 
on its lap, the valve just opening, the valve wide open, and 
the valve pushed in until it strikes the plug. With each 
valve-gear a steel-wire tram is sent. Just above the valve- 
stem on the plug-head casting, a prick-punch mark will be 
found. Loosen up the inlet stem head on the stem, then 
shove the valve back until it strikes the plug. If the valve 
is set correctly, the tram with one end in the mark on the 
plug head casting should with the other end meet the first 
scratch line on the valve-stem (nearest the outside end of 
stem). If the point of the tram does not coincide with 
this line, the valve-stem should be screwed in or out until 
it does. The valve should then be let back so that the 
dasher strikes the head, and the inlet stem head be brought 
back against the pusher plate when the pusher plate is ver- 
tical, leaving 1/64 inch clearance between the pusher and 
latch plates. It will then be found that the point of the 
tram will correspond with the fourth mark on the stem, 
with the valve closed. 



Valves and Valve Setting 417 

When the valve is moved forward so that the tram point 
corresponds with the third line on the stem^ the valve is 
just closing or openings and when moved farther so that it 
corresponds with the. second line^ the valve is wide open. 
The travel of the valve should be between the second^ third 
and fourth points spoken of^ and it should trip just as the 
tram point corresponds with the second line from the out- 
side end. Then^ with the piston on dead center^ the ec- 
centric -should be revolved on the shaft to bring the steam 
valve gV of a^ i^ch open on the crank end and 3/64 of 
an inch on the head end. The eccentric should then be 
clamped to the shafts and the valve is set. 

To Adjust the Exhaust Valves. On the outside of the 
plug head are four prick-punch marks. On the outside of 
the outlet stem head where the tram rests is another prick- 
punch mark. This is for one point of tram. 

To Adjust Valves For Lap. The eccentric rod should 
be disconnected from the eccentric. Shove the valve back 
as far as it will go. With the valve in this position^ the 
outside end of the tram should fall into the fourth mark 
on outside of the plug head nearest the cylinder. If it 
does not^ loosen up the nut holding the outlet stem head, 
and screw the stem in or out sufficiently to make the tram 
come into the fourth mark. Then tighten up the nut hold- 
ing the outlet stem head, connect the eccentric-rod to the 
eccentric, lengthen or shorten this eccentric rod so that 
the travel of the valve due to one revolution of the eccen- 
tric will move the tram from the first to the third prick- 
punch mark ; and no farther. 

The eccentric should then be set so that when the piston 
is about 5 inches from the end of the return stroke, the ex- 
haust valve should have just closed, and the tram point 
would fall into the second mark on the plug head. 



418 



Steam Engineering 




Fig. 150 
the fitchbubg engine, showing the valve gear 



Valves and Valve Setting 



419 



As these valves mnst be set while the valves are out of 
sight, a strict adherence to these rules of adjustment must 
be followed, care being taken to be accurate on all points. 




Fig. 151 
cross section of steam valve, fitchburg engine 

The Fitchburg Engine. This engine is fitted with four 
valves of the piston type. Motion is imparted to the steam 
valves by* a shaft governor eccentric, acting through rods 



420 Steam Engineering 

A and B, and wrist-cranks C and D, Fig. 150. The ex- 
haust valves have a common stem^ and receive their motion 
from a fixed eccentric through rods F^ and E^ Fig. 150. 
The construction of the steam valve is illustrated in Fig. 
151. The valve is held in place on the stem A by the nut 
B. Eings C and D fit into^ and bind in place^ taper plug 
E^ E^ which is used to set out expansible ring F^ F. 6, G, 
are adjustment bolts^ used for adjusting ring F, F^ to wear. 
To adjust the ring^ first slacken nut B just enough to allow 
ring F freedom to expand or contract, then to expand it 
slacken the bolts G, G, and run the set-screws H in until 
the required expansion is accomplished. If too tight, re- 
verse the process by first slackening set screws H, and then 
tighten bolts G. During the process the valve should be 
tested for tightness by rocking it back and forth with the 
starting bar. 

Fig. 152 shows the steam and exhaust valves for one end 
of the cylinder. The exhaust valve A is solid. The steam 
valve B is double ported, and balanced as shown in Fig. 
151. Eef erring to Fig. 152, the valve motion is on the 
center of its travel, the valves being lapped. In this posi- 
tion rocker arms C and D should stand vertical, exactly at 
right angles to the center line of the engine, and the wrist- 
cranks E and F should be in like position, with the cams 
G and H as shown, and the valve rod so adjusted that the 
valves have their proper lap. When all of the rods are 
properly adjusted as to length, the rocker-arms, and wrist- 
cranks will travel an equal distance on each side of the 
center line on which they rest in Fig. 152. Nut J on the 
steam reach rod has a right-and-left thread in it, and by 
loosening the lock nuts and turning the center, the length 
of this rod may be changed so as to bring the wrist-cranks 



Valves and Valve Setting 



421 



in line. Fig. 151 shows the steam valve just on the point 
of opening. The arrows indicate the direction of flow of 
the steam. 



c^J^fo 



Fig. 152 



Fig. 153 shows the same valve at full opening, and the 
wrist cranks at the extreme position of their travel in that 
direction. The o^overnor eccentric is also at its maximum 



422 



Steam Engineering 



throw, and on its center. One steam valve is full open, 
and the other one is closed. When the positions are re- 




FiG. 153 



versed, and the eccentric is on the other center, the steam 
valve here shown will be back in the position shown in Fig. 
152, and the crank-end valve will be full open. The ex- 



Valves and Valve Setting 423 

haust valves should be so adjusted that they will close, and 
open, alternately at about seven-eights of the stroke of the 
engine. The travel of the steam valves equals the distance 
W (Fig. 152) or the width of the bridge X, plus the width 
of the valve port Y. The steam valve is given this travel 
through the medium of the cams, and herein lies the pe- 
culiarity of this valve motion. The largest part of the cam 
slot is of the same radius that the driving pin and roll on 
the wrist-crank pass through, so that when the pin is 
moving down and away from the steam chest and back 
again to the position shown in Fig. 152, the valve is at 
rest. This is for a period of one-half the engine revolu- 
tion. To illustrate this fact, remember that while the 
wrist-crank is in the position shown in Fig. 152, it is on 
the center or half of its travel. Supposing the eccentric 
to move so that the wrist-pin moves from K to L and back 
again; the engine has completed one-half its revolution. 
Now while the same wrist-pin is traveling from the position 
shown in Fig. 152 to that in Fig. 153, the motion of open- 
ing is given in one-fourth of the engine revolution, and on 
moving back to the central position the valve has cut off 
and lapped in one-fourth of the revolution. To prevent a 
too sudden action of the valve, the slot is just enough off 
from the point M to the end to start the cam and valve in 
motion slightly before the valve opens. 

The steam valve is balanced by having the steam pres- 
sure on all sides, with the exception of the area of the valve 
stem on one end. The steam valves admit, and the ex- 
haust valves release steam over their inside ends. The 
steam valves receive motion indirectly, on account of the 
wrist-cranks. The exhaust valve motion is direct. The 
steam and exhaust eccentrics both lead the crank. 



424 



Steam Engineering 



Fig. 154 shows the relative position of the crank and 
steam eccentric at about the point A on the dotted line 
E X^ or it is about 90 degrees plus 37 degrees for lap and 
lead ahead of the cranky and the exhaust eccentric is ap- 
proximately at 90 degrees ahead of the crank. This lat- 
ter fact may be useful to know in the event of a slipped 
eccentric and the minimum time for adjustment. 




Fig. 154 



Fig. 152 shows both eccentrics at 90 degrees, while Fig. 
153 shows the lead of the steam valve distorted, for clear- 
ness of ilustration, but the wrist-crank is in the same ap- 
proximate position as when the crank is on the center and 
the eccentric is, at its greatest throw, advanced to the point 
shown in Fig. 154. While in this position the steam is cut 
off at about three-fourths stroke. The angle of advance 
grows less and less as the eccentric is thrown across the 
shaft by the action of the governor from higher speed. 



Valves and Valve Setting 425 

thus accomplishing the regulation of speed. For a full 
understanding of this action refer to Fig. 154. The action 
is as follows : As long as the engine is below speedy the ec- 
centric is kept in its longest throw by the tension of the 
springs^ and steam follows about three-fourths of the stroke, 
but as soon as the proper speed is reached, centrifugal 
action causes the weights H to overcome the tension of the 
springs and to move outward in the direction of the arrow, 
at the same time lengthening the springs. By means of 
the connecting rods G G, the outward motion of the weights 
turns the suspension arms C upon their fulcra and the 
ears B, the eccentric is carried across the shaft from S to- 
ward E, and as the arcs by the centers B B are in oppo- 
site curves they compensate each other, and the center S 
of the eccentric follows a straight line in its movement, 
preserving a constant lead opening, or otherwise, as de- 
sired. This manifestly decreases the eccentricity, and in- 
creases the advance of the eccentric, giving an earlier cut- 
off to the valve until, when the eccentric is swung squarely 
back of the crank, the valve opens only the lead, there be- 
ing all points between this and extreme cut-off for varia- 
tion. Upon the least diminution of speed the springs have 
more power than the centrifugal force of the weights, and 
the motion of the parts is arrested and turned in the op- 
posite direction, giving a later cut-off, as more work is per- 
formed by the engine. 

How to Set and Adjust the Valves. Having now dis- 
cussed the motion, the idea is to get a working knowledge 
of how to set the valves and adjust them and the governor 
for various conditions. The location of the governor case 
is determined by placing the engine on one dead center, 
and rolling the case around on the shaft until the oif set 



426 Steam Engineering 

of the eccentric is on the opposite side of the shaft from 
the crank pin. Then roll carefully into such position that 
when (with the springs removed) the eccentric is thrown 
back and forth across the shaft no end motion is given the 
valve rod. At this place tighten the governor case firmly 
upon the shafts and roll the shaft to the opposite dead 
center and again move the eccentric back and forth across 
the shafts and roll^ and if there is at this end any end mo- 
tion to the valve-rod^ change the position of the governor 
case on the shaft enough to make the motion just half as 
much^ then fasten the governor case firmly in this final 
position by drilling into the shaft for the point of the set- 
screw^ and then tightening the clamp bolts to place solidly. 
Put in the springs and tighten them until the proper num- 
ber of revolutions is obtained^ being sure to tighten up the 
springs that go through the counterbalance which hangs 
nearest the springs (when the governor is at rest) about 
three-fourths of an inch more than the springs on the other 
side. 

The travel of the exhaust valves can first be evened up 
before their eccentric is tightened upon the shaft by rolling 
the eccentric around the shaft to its extreme throw at each 
end. It should then be set so that the port is just closed 
when the crosshead has traveled a little less than seven- 
eighths of its stroke^ and the set screw firmly screwed upon 
the shaft. 

To adjust the steam valves^ place the latch of the hook 
in the center of the half-spiral slot and clamp the hook 
firmly by its lever^ evening up the movement of the wrist- 
cranks by the right and left nut in the valve-rod, so that 
in a revolution of the engine shaft they rock evenly each 
side of a vertical line drawn from the centers of their 



Valves and Valve Setting 42T 

shafts. Set the engine exactly on one dead center, and 
move the small valve rod attached to the head end valve in, 
and OTit of its cam until the port is opened the proper lead, 
in usual cases one-sixteenth of an inch, and tighten the set- 
crew in the neck of the cam npon the rod firmly. Eoll the 
engine to opposite center and set the other valve in the 
same way. After the valves are thus set as closely as pos- 
sible, if practicable they should be adjusted by use of the 
indicator, when the engine is under partial or full load, as 
no mere measurements can ever set the valves exactly right 
in any engine. The exhaust valves of the low-pressure 
cylinder can be set the same as for the high-pressure 
cylinder. 

The shaft governor depends for its action upon the cen- 
trifugal power of the two weights nearest the rim, which, 
through the connecting-rods, move the counterbalancing 
weights to which the eccentric is attached and thus carry 
the eccentric across the shaft, altering the throw of the 
valve-rod and the point of closure of the admission valves. 
The centrifugal power of the weight arms being exerted 
against the springs, and the more the weight arms are 
thrown out toward the rim, the earlier the point of cut-off, 
it follows that to increase the speed of the engine, tighten 
the springs or take off some the weight; and to decrease the 
speed, loosen the springs or add more weight. The springs 
should not be stretched much over II/2 times the length of 
the coil when unstretched. The speed of the engine may 
be changed several revolutions by adjusting the tension of 
the springs. A small amount of friction should be main- 
tained between the face of the eccentric and the governor 
case to prevent dancing, and this is secured by the springs 
and washers on the ends of the pins which carry the 



428 Steam Engineering 

counterbalance weights. Once adjusted^ they are right for 
a long time. 

Adding to the centrifugal weight arms and increasing 
the tension of the springs makes the governor more sen- 
sitiveo 



The Governor 

The proper regulation of speed is a very important point 
in the operation of engines^ and in order to attain this most 
desirable object^ due attention must be paid to the governor. 
If the governor is what is known as a throttling governor 
(see' Fig. 155), the principles of which are explained in 




Fig. 155 
throttling governor 

the section on ^^definitions/^ care should be taken to not 
pack the small valve stem too tight, nor allow the packing 
to become hard from long usage. The packing nut should 
be left loose enough to allow a slight leakage of steam past 
the stem. This will keep it lubricated, and the slightest 

429 



430 Steam Engineering 

variation of the governor balls will be transmitted to the 
valve, and the speed will be regular. 

If the engine has an automatic cut off mechanism actu- 
ated by a fly ball governor^ it is obvious that all the moving 
parts of the governor should work with as little friction as 
possible. Good oil and enough of it should be used. Par- 
ticular attention should be paid to the dash pot connected 
with the governor, the object of which is to regulate the 
variations of the governor and prevent a jerky movement. 
It often happens, especially with new engines, that the 
small piston in the dash pot fits too snug, and the conse- 
quence is that it sticks ; causing the governor to be slow in 
responding to changes in the speed of the engine. 

It is a good plan sometimes to take the dash pot piston 
out, and putting it in a lathe, reduce its diameter slightly, 
and also round off the sharp edges. The oil used in the 
dash pot should not be allowed to become gummy by being 
used too long without changing it for fresh oil. 

SHAFT GOVERNORS. 

Shaft Governors, Many automatic cut off engines, 
especially those of the high speed type, are fitted with isoch- 
ronal, or shaft governors. There are various styles of 
these governors, but all, or nearly all of them control the 
admission of steam to the cylinder, and consequently the 
point of cut ofi by varying the angular advance of the 
eccentric, which in such engines is free to move across the 
shaft, being entirely under the control of the governor. 

Very close regulation is generally obtained by the use of 
shaft governors, but particular attention should be given 
to the lubrication of the steam valve, which, with this class 
of engines, is generally a slide valve of some description. 



Shaft Governors 431 

and although it may be ever so nicely balanced, yet if it 
does not get sufficient oil, the friction due to dry surfaces 
rubbing together, will put extra work on the governor, 
and the speed is liable to be irregular. 

The general principle controlling the action of shaft- 
governors is clearly explained in the section on ^^defini- 
tions/^ and need not be restated here. A few examples 
of the various makes of this type of governor will be given. 
The shaft governor, or "^^overnor eccentric^^ as it is called, 
which is attached to the Fitchburg engine is described in 
connection with that engine. (See Fig. 154.) 

Fig. 156 shows the shaft governor of the Eussell engine, 
which is also a four valve high speed engine. 

This governor is of the centrifugal type and regulates by 
advancing the eccentric, or retarding it in its position in 
relation to the crank, thus hastening or holding the point 
of cut off without altering the travel, and the lap of valve 
remaining the same. The weights are pivoted at the ends 
of the arm by the pins near the rim of the wheel, and their 
outward motion is resisted by springs. The eccentric is 
fastened to each weight arm by links, and is counterweighted 
to offset the weight of the reciprocating parts attached. 
The governor is very simple, and easily understood. 

On a right-hand engine running over, the parts will be 
mounted as in Fig. 156, with the right-hand weight arm 
hanging down and the left-hand arm in the position shown. 
This arrangement also holds good for a left-hand engine 
running under. 

To change from a right-hand engine running over, to a 
left-hand engine running under, the wheel would be turned 
around side for side. On a right-hand engine running 
under or a left-hand engine running over, the weight arm 



432 



Steam Engineering 



will hang downward on the left^ the pin being placed in 
the vacant hole seen at the top of the spoke. To change 
from a right-hand engine running nnder^ to a left-hand 
engine running over^ turn the wheel aronnd side for side. 
In other words the weight must always follow the pivot 
pin of its arm in the direction of engine travel. 

When first working the engine np to speed for the pur- 
pose of adjusting the governor, screw up on the springs and 




Fig. 156 
centrifugal governor 



keep setting the weights out farther on the arms, until the 
speed and sensitiveness are about right. 

Then to get more speed, set up on the springs or take 
off weight. 

To get less speed, slacken the springs or add weight. 

To make the governor less sensitive, slacken the springs 
and take off weight. 



I 



Shaft Governors 433 



To make the governor more sensitive^ set np on the 
springs and add weight. 

To correct for sluggishness^, set up on the springs. 

Generally speakings when the governor regulates closely 
and a change in speed is desired^ the spring tension should 
not be changed^ but the desired speed should be obtained 
by changing the weights. More weight gives less speedy 
and less weight more speed. Moving the weights toward 
the rim of the wheel;, or moving the spring clip on the 
weight arm toward the weight to get more purchase^ has 
the eflfect of less weight. Moving the weights toward the 
hub of the wheels or the spring clip away from the weight, 
has the effect of more weight. 

To move the spring clip too far affects the sensitiveness 
of the governor as well as the speedy and a radical change 
should not be made without the advice of the builders. 
When changes of tension on the spring or in the amount 
of weight are made in any way, the same amount of change 
should always be made on each spring or weight, as the 
case may be. To change the direction of rotation on one 
of these engines, turn the eccentrics to positions opposite 
to those for the initial direction, and hang the weight arms 
according to the directions here given. 

Fig. 157 shows the Atlas shaft governor which regulates 
the supply of steam to the engine by lengthening, or short- 
ening the valve travel, according as the load increases or 
diminishes. 

The movement of the governor parts thus not only con- 
trols the speed of the engine under changes of load how- 
ever wide, but also offers proper conditions for low steam 
consumption. 



434 



Steam Engineering 



The eccentric is pivoted on the same side of the shaft 
as the cranky and as the eccentric swings across the shaft, 
decreasing valve travel, the lead is well maintained 
throughout all working conditions of the engine, insuring 
prompt opening of the steam ports, with consequent proper 
steam distribution. 




Fig. 157 

atlas automatic shaft governor 

Four-Yalve Center Crank Type 



The important principle of inertia is made effective in 
this governor by the manner of weight suspension. This 
is combined with a very strong centrifugal element, with- 
out which no governor is reliable. 

The Atlas engine company also supply a so-called inertia, 
or dead wheel governor for use on their automatic heavy 
duty (side crank) engines. This governor occupies less 
space than does the band-wheel type, but is nevertheless a 
governor of great power, because of the large inertia ele- 



Shaft Governors 435 

ment stored in the wheel. This wheel is not keyed to the 
shafts but is free to turn thereon and by such motion 
through link connection with the eccentric^ combined with 
the centrifugal action of two weights^ the eccentric is 
shifted across the shafts changing the angle of advance. 

Fig. 158 shows a view of this governor. Both of these 
governors have spiral springs acting in compression^ not in 
tension. 




Fig. 158 

the atlas automatic shaft governor 

Side Crank Type 

Figs. 159 and 160 show views of the Armington and Sims 
shaft governor^ which differs in some respects from those 
already described^, notably in that it has two eccentrics, one 
working inside the other. Referring to Fig. 159 it will 
be seen that it consists of a wheel which is fixed to the 
engine shaft, to which are hinged the weights 1, 1 ; these 
weights are controlled by springs, one end of the same be- 



436 



Steam Engineering 



ing seated in a pocked fixed on the spoke of the wheels or 
in some cases attached directl}- to rim of wheel; the inner 
eccentric, marked C, having ears attached, is placed close 
to the regulator wheel, and is free to turn upon the shaft ; 
from these ears rods 2, 2 are connected with the weights : 




Fig. 159 
armington and sims shaft governor 

on the outside of the inner eccentric and free to turn is 
placed an eccentric ring D, from which a rod 3 is connected 
to the toe of one of the weights; on this outer eccentric 
ring is placed the usual eccentric strap, to which is directly 
attached the valve rod. To avoid confusion, these are not 
shown in the cut. 



Shaft Governors 



437 



It will be seen that when the engine is running at its 
greatest velocity the weights^ due to the centrifiigal force 
overcoming the springs^ will be ont^ consequently the posi- 
tion of the eccentrics will be as shown in Fig. 159, which 
gives the valve its least travel and shortest cut-off. The 




Fig. 160 
aemington and sims shaft governor 

eccentricity of the two combined eccentrics is then the dis- 
tance shown at A^ in the cut. 

Taking now the other extreme position shown in Fig. 
160 when the engine has its heaviest load, requiring later 
cut off. The position of the weights will then be as shown 
in the cut^ and it will be seen that when the weights are in 



438 Steam Engineering 

this position^ the inner eccentric has been moved back^ and 
the outer eccentric forward or in the opposite direction^ 
and the eccentricity by this combined movement is in- 
creased as shown at B ; this is sufficient to allow the steam 
to follow the piston to about seven-tenths of the stroke. 
This gives a wide range of valve action^ practically from 
simple lead at A^ Pig. 159^ to admission during seven- 
tenths of the stroke, and causes very quick and sensitive 
action resulting in close regulation. The lead of the valve 
remains constant at all positions of the eccentrics. 

QUESTIONS AND ANSV7ERS. 

316. What inportant features in the operation of an 
engine are dependent upon a correct adjustment of the 
valves ? 

Ans. The efficiency of the engine, the economical" use 
of steam, and the regular and quiet action of the engine. 

317. How many different types of valves are there in 
general use? 

A71S. Slide, poppet, rotative, piston, gridiron, etc. 

318. What are the basic principles governing the ad- 
justment of the valves of an engine, regardless of the type? 

Ans. Admission, cut-off, release, and exhaust closure; 
each of these functions to occur at the proper moment dur- 
ing one stroke of the piston. 

319. ISFame two important functions of a valve. 
Ans. Lap and lead. 

' 320. What is the effect of increasing outside lap? 

Ans. Later admission, and an earlier cut off. 

321. What results from increasing inside lap? 

Ans. Earlier exhaust closure, and an increased conpreS" 
sion. 



Questions and Answers 439 

322. What advantage has an engine of the four valve 
type over a single valve engine? 

Ans. Each individual valve may be adjusted in- 
pendently of the others. 

323. If a valve had neither lap nor lead what would 
be the position of the eccentric relative to the crank? 

Ans. 90° ahead of the crank. 

324. What is meant by the term ^^angular advance/^ and 
why is it necessary ? 

Ans, The distance that the high point of the eccentric 
is set ahead of a line at right angles with the crank. It is 
necessary in order to give the valve lap, and lead. 

325. What is the first function of the valve at the com- 
mencement of the stroke ? 

Ans. Lead, or admission. 

326. What is the second function? 
Ans. Pull port opening. 

327. What is the travel of a valve equal to? 

Ans. Twice the port opening plus twice the outside lap. 

328. What is the third function of the valve? 
Ans. Cut off. 

329. What is the fourth function? 
Ans. Exhaust closure, or compression. 

330. What will be the effect if the valve has no inside 
lap? 

Ans. An early release, and no compression. 

331. What is meant by ^^radius of eccentricity?^^ 
' Ans. One half the travel of the valve. 

332. What is an eccentric? 

Ans. A mechanical device for converting rotary into 
reciprocating motion. Its center of revolution is apart 
irom its center of formation. 



440 Steam Engineering 

333. What is the "^^throw'^ of an eccentric? 

Ans. The distance from the center of the eccentric to 
the center of the shaft. 

334. What is meant by eccentric position? 

Ans. The location of the highest point of the eccentric 
relative to the center of the crank pin^ expressed in degrees. 

335. What is valve travel? 

Ans. The distance covered by the valve in its move- 
ment. 

336. What is lap? 

Ans. The amount that the ends of the valve project 
over the edges of the ports when the valve is at mid travel. 

337. What is inside lap ? 

Ans. The lap of the inside^ or exhaust edge of the valve 
over the inside edge of the port. 

338. What is outside lap ? 

Ans. The lap of the outside edge of the valve over the 
outside edge of the port. 

339. What is lead? 

Ans. The amount that the port is open when the crank 
is on the dead center. 

340. Why must a valve have outside lap ? 

Ans. Because admission and cut off are controlled 
thereby. 

341. Why should a valve have inside lap ? 

Ans. In order that release and compression may be 
properly controlled. 

342. What is the effect of decreasing the angular ad- 
vance ? 

Ans. All the important functions of the valve occur 
later. 

343. " What results follow from decreasing the travel of 
the valve 



I 



Questions and Answers 441 



Ans. Less lead^ a later admission and release, and an 
earlier cut off and compression. 

344. What is meant by automatic or variable cut off? 
Ans. A system in which full boiler pressure is constantly 

maintained in the valve chest, the speed being regulated by 
the governor controlling the point of cut off. 

345. What is meant by fixed cut off? 

Ans, When the point of cut off remains the same, re- 
gardless of the load, the speed being regulated by throttling 
the steam. 

346. What three changes must be made in order to 
cause an earlier cut off on an engine that has a fixed cut off ? 

Ans. First — Incijease the angular advance. Second — 
Increase the outside lap. Third — Increase the inside lap. 

347. What is the first step in valve setting? 
Ans. To place the engine on the dead center. 

348. What is meant by the dead center? 

Ans. When the piston is at the end of the stroke, and 
the centers of the crank shaft, crank pin, and cross head 
pin are in line. 

349. What rule should be observed in turning an en- 
gine to place it on the dead center? 

Ans. Always turn it in the direction in which it is to 
run. 

350. Why is this necessary? 

Ans. In order to guard against errors which might 
result from lost motion in the parts. 

351. Having placed the engine on the dead center, what 
is to be done next ? 

Ans. Adjust the eccentric rod to the proper length? 

352. What should be done with the valve before con- 
necting it with the eccentric rod ? 

Ans. It should be placed at mid travel, and marked. 



442 Steam Engineering 

353. What is necessary before the valve can be placed 
in its central position? 

Ans, The exact amount of ontside lap must be known. 

354. What amount of lead is usually given to the valve ? 
Ans. From gV in. to % in. depending upon the size of 

the engine. 

355. What is the function of the governor? 

Ans, To properly regulate the speed of the engine. 

356. Explain the action of a governor? 

Ans. Its action is based upon the principle of the cen- 
trifugal, and centripetal forces, which cause the balls or 
weights attached to the arms, to fly outward or inward as 
their speed of revolution increases or decreases. 

357. In what manner is this movement of the balls 
caused to regulate the speed? 

Ans. In the pendulum or fly ball governor, the motion 
is transferred by means of levers and rods to the cut off 
mechanism. In the shaft governor the changes in the 
position of the weights change the angular advance of the 
eccentric, thus causing an earlier or later cut off, according 
as the load is light, or heavy. 

358. In what way does the throttling governor regulate 
the speed of an engine? 

Ans. It controls the position of a valve in the steam 
pipe, opening or closing it according as the engine needs 
more, or less steam to maintain a regular speed. 

359. What is compression? 

Ans. If the exhaust port is closed by the valve, just be- 
fore the piston reaches the end of stroke, a portion of the 
steam will be entrapped in the cylinder, and being ahead 
of the piston will be compressed. 

360. Is there any advantage in this? 




Questions and Answers 443 

\Ans. Yes. The steam thus compressed acts as a cush- 
ion for the piston^ preventing shock or jar to the moving 
parts on reaching the end of the stroke. 

361. What is an adjustable cut off? 

Ans, One in which the point of cut off may te adjusted 
by a hand wheel attached to the valve stem of a throttling 
governor. 



Definitions 

In order to facilitate the study and analysis of indicator 
diagrams, the following definitions of technical terms, some 
of which have already been explained in another part of 
this book, are here given. 

Absolute pressure. Pressure reckoned from a perfect 
vacuum. It equals the boiler pressure plus the atmospheric 
pressure. 

Boiler pressure or gauge pressure. Pressure above the 
atmospheric pressure as shown by the steam gauge. 

Initial pressure. Pressure in the cylinder at the begin- 
ning of the stroke. 

Terminal pressure (T. P.). The pressure that would ex- 
ist in the cylinder at the end of the stroke provided the 
exhaust valve did not open until the stroke was entirely 
completed. It may be graphically illustrated on the diagram 
by extending the expansion curve by hand to the end of 
the stroke. It is found theoretically by dividing the pres- 
sure at point of cut off by the ratio of expansion. Thus, 
absolute pressure at cut off =100 lbs., ratio of expansions 
5; then 100^5=20 lbs., absolute terminal pressure. 

Mean effective pressure (M. E. P.). The average pressure 
acting upon the piston throughout the stroke minus the 
back pressure. 

Back pressure. Pressure which tends to retard the for- 
ward stroke of the piston. Indicated on the diagram from 
a non-condensing engine by the height of the back pressure 
line above the atmospheric line. In a condensing engine 
the degree of back pressure is shown by the height of the 

145 



446 Steam Engineering 

back pressure line above an imaginary line representing 
the pressure in the condenser corresponding to the degree 
of vacuum in inches, as shown by the vacuum gauge. 

Total or absolute bach pressure, in either a condensing 
or non-condensing engine, is that indicated on the diagram 
by the height of the line of back pressure above the line 
of perfect vacuum. 

Ratio of expansion. The proportion that the volume of 
steam in the cylinder at point of release bears to the volume 
at cut off. Thus, if the point of cut off is at one-fifth of 
the stroke, and release does not take place until the end 
of the stroke, the ratio of expansion, or in other words, the 
number of expansions, is 5. When the T. P. is known the 
ratio of expansion may be found by dividing the initial 
pressure by the T. P. 

Wire drawing. When through insufficiency of valve 
opening, contracted ports, or throttling governor, the steam 
is prevented from following up the piston at full initial 
pressure until the point of cut off is reached, it is said to 
be wire drawn. It is indicated on the diagram by a grad- 
ual inclination downwards of the steam line from the ad- 
mission line to the point of cut off. Too small a steam pipe 
from boiler to engine will also cause wire drawing, and fall 
of pressure. 

Condenser pressure may be defined as the pressure exist- 
ing in the condenser of an engine, caused by the lack of a 
perfect vacuum. As, for instance, with a vacuum of 25 
in. there will still remain the pressure due to the 5 in. which 
is lacking. This will be about 2.5 lbs. 

Vacuum, That condition existing within a closed ^^ssel 
from which all matter, including air, has been expelled. 
It is measured by inches in a column of mercury contained 



Definitions 447 

within a glass tube a little over 30 in. in height^ having its 
lower end open and immersed in a small open vessel filled 
with mercury. The upper end of the glass tube is con- 
nected with the vessel in which the vacuum is to be pro- 
duced. When no vacuum exists the mercury will leave the 
tube and fill the lower vessel. When a vacuum is main- 
tained in the condenser, or other vessel, the mercury will 
rise in the glass tube to a height corresponding to the de- 
gree of vacuum. If the mercury rises to the height of 30 
in. it indicates a perfect vacuum, which means the absence 
of all pressure within the vessel, but this condition is never 
realized in practice ; the nearest approach to it being about 
28 in. 

For purposes of convenience the mercurial vacuum gauge 
is not generally used, it having been replaced by the Bour- 
don spring gauge, although the mercury gauge is used for 
testing. 

The vacuum in a condenser is generally maintained by 
an air pump, although it can be produced and maintained 
by the mere condensation of the steam as it enters the con- 
denser by allowing a spray of cold water to strike it. The 
steam when it first enters the condenser drives out the air 
and the vessel is filled with steam which, when condensed, 
occupies about 1,600 times less space than it did before be- 
ing condefised, hence a partial vacuum is produced. 

While the vacuum in a condenser cannot be considered 
as power at all, yet it occupies the anomalous position of 
increasing, by its presence, the capacity of the engine for 
doing work. This is owing to the fact that the atmospheric 
pressure, or resistance which is always ahead of the piston 
in a non-condensing engine is, in the case of a condensing 
engine, removed to a degree corresponding to the height of 



448 Steam Engineering 

the vacuum, thus making available just so much more of 
the pressure behind the piston. Thus, if the average steam 
pressure throughout the stroke is 30 lbs. and there is a 
vacuum of 26 in., maintained in the condenser, there will 
be 13 lbs. of resistance per square inch removed from in; 
front of the piston, thus making available 30+13=43 lbs. 
pressure per square inch. 

Absolute zero has been fixed by calculation at 461.3° be- 
low the zero of the Fahrenheit scale. 

Piston displacement. The space or volume swept through 
by the piston in a single stroke. Found by multiplying 
the area of piston by length of stroke. 

Piston clearance. The distance between the piston and 
cylinder head when the piston is at the end of the stroke. 

Steam clearance, ordinarily termed clearance. The space 
between the piston at the end of the stroke and the valve 
face. It is reckoned in per cent of the total piston dis- 
placement. 

Horse power (H. P,). 33,000 pounds raised one foot 
high in one minute of time. 

Indicated horse power (I, H. P.), The horse power as 
shown by the indicator diagram. It is found as follows : 

Area of piston in square inches XM. E. P. X piston speed 
in feet-^33,000. 

Piston speed. The distance in feet traveled by the piston 
in one minute. It is the product of twice the length of 
stroke expressed in feet, multiplied by the number of revolu- 
tions per minute. 

R, P. M. Eevoluiions per minute. 

Net horse power. I. H. P. minus the friction of the en- 
gine. 



Definitions 449 

Compression. The action of the piston as it nears the 
end of the stroke^ in reducing the volume^ and raising the 
pressure of the steam retained in the cylinder ahead of the 
piston by the closing of the exhaust valve. 

Boyle's or Mariotte's law of expanding gases, ^^The pres- 
sure of a gas at a constant temperature varies inversely as 
the space it occupies/^ Thus^ if a given volume of gas is 
confined at a pressure of 50 lbs. per square inch and it is 
allowed to expand to twice its volume^ the pressure will fall 
to 25 lbs. per square inch. 

Adiahatic curve. A curve representing the expansion 
of a gas which loses no heat while expanding. Sometimes 
called the curve of no transmission. 

Isothermal curve. A curve representing the expansion 
of a gas having a constant temperature but partially in- 
fluenced by moisture^ causing a variation in pressure accord- 
ing to the degree of moisture or saturation. It is also 
called the theoretical expansion curve. 

Expansion curve. The curve traced upon the diagram 
by the indicator pencil showing the actual expansion of 
the steam in the cylinder. 

First law of thermodynamics. Heat and mechanical 
energy are mutually convertible. 

Power. The rate of doing work^ or the number of foot 
pounds exerted in a given time. 

Unit of work. The foot pound, or the raising of one 
pound weight one foot high. 

First law of motion. All bodies continue either in a 
state of rest or of uniform motion in a straight line, except 
in so far as they may be compelled by impressed forces to 
change that state. 

Work. Mechanical force or pressure cannot be con- 



450 Steam Engineering 

sidered as work iinless it is exerted iipon a body and causes 
that body to move through, space. The product of the 
pressure multiplied by the distance passed through and 
the time thus occupied is work. 

Momentum. Force possessed by bodies in motion, or 
the product of mass and density. 

Dynamics. The science of moving powers or of matter 
in motion, or of the motion of bodies that mutually act upon 
each other. 

Force. That which alters the motion of a body, or puts 
in motion a body that was at rest. 

Maximum theoretical duty of steam is the product of the 
mechanical equivalent of heat, viz., 778 ft. lbs. multiplied 
by the total heat units in a pound of steam. Thus, in one 
pound of steam at 212° reckoned from 32° the total heat 
equals 1,146.6 heat units. Then 778X1,146.6 equals 892,- 
054.8 ft. lbs.=maximum duty. 

Steam efficiency may be expressed as follows : 

Heat converted into useful work 

and maximum efficiency 

Heat expended 

can only be attained by using steam at as high an initial 
pressure as is consistent with safety, and at as large a ratio 
of expansion as possible. The percentage of efficiency of 
steam used at atmospheric pressure in a non-expansive en- 
gine is very low ; as, for instance, the heat expended in the 
evaporation of one pound of water at 32° into steam at 
atmospheric pressure=l,146.6 heat units, and the volume 
of steam so generated=26.36 cu. ft. 

One cubic foot of steam at 212° contains energy equal 
to 144X14.7=2,116.8 ft. lbs., and 26.36 cu. ft.=2,116.8 
X 26.36=55,798.84 ft. lbs., which divided by the mechani- 
cal equivalent of heat, viz., 778 ft. lbs.=71.72 heat units, 



Definitions 451 

available for useful work. The per cent of efficiency there- 

71.72X100 

fore is =6.2 per cent. But suppose the initial 

1,146.6 

pressure to have been 200 lbs. absolute, and that the steam 

is allowed to expand to thirty times its original volume. 

The heat expended in evaporating a pound of water at 32 ^ 

into steam at 200 lbs. absolute pressure=l,198.3 heat units, 

and the volume of steam so generated=2.27 cu. ft. The 

average pressure during expansion would be 29.34 lbs. per 

square inch and the volume when expanded thirty times 

would equal 2.27X30=68.1 cu. ft. 

One cubic foot of steam at 29.34 lbs. pressure equals 
144X^9.34=4,224.96 ft. lbs., and 68.1 cu. ft. will equal 
4224.96X68.1=287,719.7 ft. lbs. of energy, which divided 
by the equivalent, 778, equals 370.2 heat units, and the per 

cent of efficiency will be — 7T^5~^ — =30.8 per cent. 

. Engine .efficiency. If the engine is considered merely as^ 
a machine for converting into useful work the heat energy 
in the steam regardless of the cost of fuel, its efficiency 
may be expressed as follows : 

Heat converted into useful work 



Total heat received in the steam 
Example. Assume an engine to be receiving steam at 
95 lbs. absolute pressure, that the consumption of dry 
steam per horse power per hour equals 20 lbs., that the 
friction of the engine amounts to 15 per cent, and that the 
temperature of the feed water is raised from 60° to 170° 
by utilizing a portion of the exhaust. 

In a pound of steam at 95 lbs. absolute there are 1,180.7 
heat units, and in a pound of water at 170° there are 



452 Steam Engineering 

138.6 units of heat^ but 28.01 of these heat units were in 
the water at its initial temperature of 60^. Therefore the 
total heat added to the water by the exhaust steam equals 
138.6—28.01=110.59 heat units, and the total heat in 
each pound of steam to be charged up to the engine is 1,180.7 
— 110.59=1,070.11, and the total for each horse power de- 
veloped per hour will be 1,070.11X^0=21,402.2 heat units. 
A horse power equals 33,000 ft. lbs. per minute, or sixty 
times 33,000=1,980,000 ft. lbs. per hour. From this must 
be deducted 15 per cent for friction of the engine, leaving 
1,683,000 ft. lbs. for useful work. Dividing this by the 
equivalent, viz., 778 ft. lbs., gives 2,163.2 heat units as the 
heat converted into one horse power of work in one hour, 
and the percentage of efficiency of the engine will be 

2,163.2X100 

• ^=:10.1 per cent. 

21,402.2 

Efficiency of the plant as a whole includes boiler and 

engine efficiency, and is to be figured upon the basis of 

Heat converted into useful work 



Calorific or heat value of fuel 

Horse power constant of an engine is found by multiply- 
ing the area of the piston in square inches by the speed of 
the piston in feet per minute and dividing the product by 
33,000. It is the power the engine would develop with one 
pound mean effective pressure. To find the horse power of 
the engine, multiply the M. E. P. of the diagram by this 
constant. 

Logarithms. A series of numbers having a certain rela- 
tion to the series of natural numbers, by means of which 
many arithmetical operations are made comparatively easy. 
The nature of the relation will be understood by considering 
two simple series, such as the following, one proceeding 



Definitions 453 

from unity in geometrical progression and the other from 
in arithmetical progression: 

Geom. series, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. 

Arith. series, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, etc. 

Here the ratio of the geometrical series is 2 and any 
term in the arithmetical series expresses how often 2 has 
been multiplied into 1 to produce the corresponding term 
of the geometrical series. Thus, in proceeding from 1 to 
32 there have been 5 steps or multiplications by the ratio 
2; in other words, the ratio of 32 to 1 is compounded 5 
times of the ratio of 2 to 1. The above is the basic princi- 
ple upon which common logarithms are computed. 

Hyperbolic logarithms. Used in jfiguring the M. E. P. 
of a diagram from the ratio of expansion and the initial 
pressure. Thus, hyperbolic logarithm of ratio of expansion 
+ 1 multiplied by absolute initial pressure, and divided by 
ratio of expansion=mean forward pressure. Prom this 
deduct total back pressure and the remainder will be mean 
effective pressure. The hyperbolic logarithm is found by 
multiplying the common logarithm by the constant 2.302- 
585. Table 33 gives the hyperbolic logarithms of numbers 
usually required in calculations of the above nature. 



454 



Steam Engineering 



Table 33 
hyperbolic logarithms. 



No. 


Log. 


No. 

~3j00^ 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


Tor 


0.0099 


1.0986 


5.00 


1.6094 


7.00 


~r9459~ 


9.00 


2.1972 


1.05 


0.0487 


3.05 


1.1151 


5.05 


1.6194 


7.05 


1.9530 


9.05 


2.2028 


1.10 


0.0953 


3.10 


1.1341 


5.10 


1.6292 


7.10 


1.9600 


9.10 


2.2083 


1.15 


0.1397 


3.15 


1.1474 


5.15 


1.6390 


7.15 


1.9671 


9.15 


2.2137 


1.20 


0.1823 


3.20 


1.1631 


5.20 


1.6486 


7.20 


1.9740 


9.20 


2.2192 


1.25 


0.2231 


3.25 


1.1786 


5.25 


1.6582 


7.25 


1.9810 


9.25 


2.2246 


1.30 


0.2623 


3.30 


1.1939 


5.30 


1.6677 


7.30 


1.9879 


9.30 


2.2310 


1.35 


0.3001 


3.35 


1.2090 


5.35 


1.6771 


7.35 


1.9947 


9.35 


2.2354 


1.40 


0.3364 


3.40 


1.2238 


5.40 


1.6864 


7.40 


2.0015 


9.40 


2.2407 


1.45 


0.3715 


3.45 


1.2384 


5.45 


1.6956 


7.45 


2.0018 


9.45 


2.2460 


1.50 


0.4054 


3.50 


1.2527 


5.50 


1.7047 


7.50 


2.0149 


9.50 


2.2513 


1.55 


0.4382 


3.55 


1.2669 


5.55 


L7138 


7.55 


2.0215 


9.55 


2.2565 


1.60 


0.4700 


3.60 


1.2809 


5.60 


1.7228 


7.60 


2.0281 


9.60 


2.2618 


1.65 


0.5007 


3.65 


1.2947 


5.65 


1.7316 


7.65 


2.0347 


9.65 


2.2670 


1.70 


0.5306 


3.70 


1.3083 


5.70 


1.7405 


7.70 


2.0412 


9.70 


2.2721 


1.75 


0.5596 


3.75 


1.3217 


5.75 


1.7491 


7.75 


2.0477 


9.75 


2.2773 


1.80 


0.5877 


3.80 


1.3350 


5.80 


1.7578 


7.80 


2.0541 


9.80 


2.2824 


1.85 


0.6151 


3.85 


1.3480 


5.85 


1.7664 


7.85 


2.0605 


9.85 


2.2875 


1.90 


0.6418 


3.90 


1.3610 


5.90 


1.7750 


7.90 


2.0668 


9.90 


2.2925 


1.95 


0.6678 


3.95 


1.3737 


5.95 


1.7834 


7.95 


2.0731 


9.95 


2.2976 


2.00 


0.6931 


4.00 


1.3863 


6.00 


1.7918 


8.00 


2.0794 


10.00 


2.3026 


2.05 


0.7178 


4.05 


1.3987 


6.05 


1.8000 


8.05 


2.0857 


10.25 


2.3273 


2.10 


0.7419 


4.10 


1.4010 


6.10 


1.8083 


8.10 


2.0918 


10.50 


2.3514 


2.15 


0.7654 


4.15 


1.4231 


6.15 


1.8164 


8.15 


2.0988 


10.75 


2.3749 


2.20 


0.7885 


4.20 


1.4351 


6.20 


1.8245 


8.20 


2.1041 


11.00 


2.3979 


2.25 


0.8110 


4.25 


1.4469 


6.25 


1.8326 


8.25 


2.1102 


12.00 


2.4849 


2.30 


0.8329 


4.30 


1.4586 


6.30 


1.8405 


8.30 


2.1162 


13.00 


2.5626 


2.35 


0.8544 


4.35 


1.4701 


6.35 


1.8484 


8.35 


2.1222 


14.00 


2.6390 


2.40 


0.8755 


4.40 


1.4816 


6.40 


1.8563 


8.40 


2.1282 


15.00 


2.7103 


2.45 


0.8961 


4.45 


1.4929 


6.45 


1.8640 


8.45 


2.1342 


16.00 


2.7751 


2.50 


0.9163 


4.50 


1.5040 


6.50 


1.8718 


8.50 


2.1400 


17.00 


2.8332 


2.55 


0.9361 


4.55 


1.5151 


6.55 


1.8795 


8.55 


2.1459 


18.00 


2.8903 


2.60 


0.9555 


4.60 


1.5260 


6.60 


1.8870 


8.60 


2.1518 


"19.00 


2.9444 


2.65 


0.9746 


4.65 


1.5369 


6.65 


1.8946 


8.65 


2.1576 


20.00 


2.9957 


2.70 


0.9932 


4.70 


1.5475 


6.70 


1.9021 


8.70 


2.1633 


21.00 


8.0445 


2.75 


1.0116 


4.75 


1.5581 


6.75 


1.9095 


8.75 


2.1690 


22.00 


3.0910 


2.80 


1.0296 


4.80 


1.5686 


6.80 


1.9169 


8.80 


2.1747 


23.00 


3.0355 


2.85 


1.0473 


4.85 


1.5790 


6.85 


1.9242 


8.85 


2.1804 


24.00 


3.1780 


2.90 


1.0647 


4.90 


1.5892 


6.90 


1.9315 


8.90 


2.1860 


25.00 


3.2189 


2.95 


1.0818 


4.95 


1.5994 


6.95 


1.9387 


8.95 


2.1916 


30.00 


3.3782 



Steam consumption per horse power per hour. The 
weight in pounds of steam exhausted into the atmosphere, 
or into the condenser in one hour^ divided by the horse 
power developed. It is determined from the diagram by 
selecting a point in the expansion curve just previous to 
the opening of the exhaust valve^ and measuring the absolute 
pressure at that point. Then the piston displacement up 
to the point selected, plus* the clearance space, expressed in 



Definitions 455 

cubic feet, will give the volume of steam in the cylinder, 
which multiplied by the weight per cubic foot of steam at 
the pressure as measured will give the weight of steam con- 
sumed during one stroke. From this should be deducted 
the steam saved by compression as shown by the diagram, 
in order to get a true Measure of the economy of the engine. 
Having thus determined the weight of steam consumed for 
one stroke, multiply it by twice the number of strokes per 
minute and by 60, which will give the total weight con- 
sumed per hour. This divided by the horse power will 
give the rate per horse power per hour. 

Cylinder condensation and reevaporation. When the ex- 
haust valve opens to permit the exit of the steam there is a 
perceptible cooling of the walls of the cylinder, especially 
in condensing engines when a high vacuum is maintained. 
This results in more or less condensation of the live steam 
admitted by the opening of the steam valve; but if the 
exhaust valve is caused to close at the proper time so as to 
retain a portion of the steam to be compressed by the piston 
on the return stroke, a considerable portion of the water 
caused by condensation will be reevaporated into steam by 
the heat and consequent rise in pressure caused by com- 
pression. 

Ordinates. Parallel lines drawn at equal distances apart 
across the face of the diagram, and perpendicular to the 
atmospheric line. They serve as a guide to facilitate the 
measurement of the average forward pressure throughout 
the stroke, or the pressure at any point of the stroke if 
desired. 

Eccentric, A mechanical device used in place of a crank 
for converting rotary into reciprocating motion. An eccen- 
tric is in fact a form of crank in which the crank pin, cor- 
responding to the eccentric sheave, embraces the shaft, but 



456 Steam Engineering 

owing to the great leverage at which the friction between 
the sheave and the strap acts^ compared with its short turn- 
ing leverage^, it can only be used to advantage for the pur- 
pose named above. 

Eccentric throw is the distance from the center of the 
eccentric to the center of the shaft. This definition also 
applies to the term ^*^radius of eccentricity.^^ 

Eccentric position. The location of the highest point 
of the eccentric relative to the center of the crank pin, 
measured or expressed in degrees. 

Angular advance. The distance that the high point of 
the eccentric is set ahead of a line at right angles with the 
crank. In other words^ the lap angle plus the lead angle. 
If a valve had neither lap nor lead^ the position of the high 
point of the eccentric would be on a line at right angles with 
the crank; as for instance, the crank being at 0^ the eccen- 
tric would stand at 90°. 

Valve travel. The distance covered by the valve in its 
movement. It equals twice the throw of the eccentric. This 
refers to engines having a fixed cut off. In the case of an 
engine with a variable automatic cut off, the travel of the 
cut off valve is regulated by the governor. 

Lap, The amount that the ends of the valve project 
over the edges of the ports when the valve is at mid travel. 

Outside or steam lap. The amoiiint that the end of the- 
valve overlaps or projects over the outside edge of the steam 
port. 

Inside lap. The lap of the inside or exhaust edge of the 
valve over the inside edge of the port. 

Lead, The amount that the port is open when the crank 
is on the dead center. The object of giving a valve lead is 
to supply a cushion of live steam which, in conjunction with 



Definitions 457 

that already confined in the clearance space by compression, 
shall serve to bring the moving parts of the engine to rest 
quietly at the end of the stroke^ and also quicken the action 
of the piston in beginning the return stroke. 

Compression. Closing of the exhaust passage before the 
steam is entirely exhausted from the cylinder. A certain 
quantity of steam is thus compressed into the clearance 
space. 

Throttling governor. Used to regulate the speed of en- 
gines having a fixed cut off. The governor controls the 
position of a valve in the steam pipe, opening or closing it 
according as the engine needs more or less steam in order 
to maintain a regular speed. 

Automatic or variable cut off. In engines of this type 
the full boiler pressure is constantly in the valve chest and 
the speed of the engine is regulated by the governor con- 
trolling the point of cut off, causing it to take place earlier 
or later, according as the load on the engine is lighter or 
heavier. 

Fixed cut off. This term is applied to engines in which 
the point of cut off remains the same regardless of the load, 
the speed being regulated by a throttling governor as ex- 
plained above. 

Isochronal or shaft governor. This device in which the 
centrifugal and centripetal forces are utilized, as in the 
fly ball governor, is generally applied to automatic cut off 
engines having reciprocating or slide valves. It is attached 
to the crank shaft, and its function is to change the position 
of the eccentric, which is free to move across the shaft 
within certain prescribed limits, but is at the same time 
attached to the governor. The angular advance of the 
eccentric is thus increased or diminished, in fact is entirely 



458 Steam Engineering 

under the control of the governor, and cut off occurs earlier 
or later according to the demands of the load on the engine. 
Adjustable cut of. One in which the point of cut off 
may be regulated or adjusted by hand by means of a hand 
wheel and screw attached to the valve stem, the supply of 
steam being regulated by a throttling governor. 

QUESTIONS AND ANSWERS. 

362. What is absolute pressure? 

Ans. Pressure reckoned from a perfect vacuum. 

363. What is gauge pressure? 

Ans. Pressure above atmospheric pressure. 

364. What is initial pressure? 

Ans. Pressure in the cylinder at the beginning of the 
stroke. 

365. What is terminal pressure? 

Ans. Pressure in the cylinder at the end of the stroke. 

366. What is mean effective pressure (M. E. P.) ? 
Ans. The average pressure acting upon the piston 

throughout the stroke. 

367. What is back pressure? 

Ans. Pressure tending to retard the forward stroke of 
the piston. 

368. What is absolute back pressure? 

Ans. Back pressure measured from a perfect vacuum. , 

369. What is the ratio of expansion ? - 

; Ans. The relative volume of steam in the cylinder at 
point of release, compared to volume at cut off. 
Jh^?70. What is wire drawing of steam? 
-■'Ans. Eestricted passage of the steam caused by too 
small a steam; pipe. 
'371. What is condenser pressure? 



Questions and Answers 459 

Ans, Pressure existing in the condenser caused by the 
lack of vacuum. 

372. What is vacuum? 

Ans, That condition existing within a closed vessel from 
iwhich all matter^ including air has been expelled. 

373. What is absolute zero? 
Ans, 461.2° below zero Fahr. 

374. What is piston displacement? 

Ans, The space swept through by the piston in a single 
stroke. 

375. What is piston clearance? 

Ans. The distance between the piston and cylinder head 
at the end of the stroke. 

376. What is steam clearance? 

Ans. The distance between the piston at end of stroke, 
and the valve face. 

377. What is a horse power (H. P.) ? 

Ans. 33^000 lbs. raised one foot in one minute of time, 

^ 378. What is indicated horse power (I. H. P.) ? 

^ ■ Ans. The horse power as shown by the indicator dia- 
gram. 

379. What is piston speed? 

Ans. The distance in feet traveled by the piston in one 
minute. 

380. Give the rule for figuring the horse power ? 

Ans. Area.of piston in square inches XM. E. P.Xpiston 
speed-^33,000. 

381. What is net horse power? 
Ans. I. H. P. minus engine friction. 

382. Define Boyle^s law of expanding gases? 

Ans. Pressure at constant temperature varies inversely 
as the space it occupies. 



460 Steam Engineering 

383. What is an adiabatic curve? 

Ans, The curve of expanding gas that loses no heat 
while expanding. 

384. What is an isothermal curve ? 

Ans, The curve of an expanding gas of constant tem- 
perature^ but influenced by moisture. 

385. What is an expansion curve? 

Ans. The curve traced upon the diagram by the indi- 
cator pencil. 

386. Define the first law of thermodynamics. 

Ans, Heat and mechanical energy are mutually con- 
vertible. 

387. What is power? 

Ans, The rate of doing work. 

388. What is the unit of work? 

Ans, The foot pounds viz., the raising of one pound, 
one foot high. 

389. Define the first law of motion? 

Ans, All bodies continue either in a state of rest, or of 
uniform motion in a straight line, unices compelled by im- 
pressed forces to change that state. 

390. What is work, mechanically considered? 
Ans, Pressure X distance passed through X time. 

391. What is momentum? 
Ans, MassX density. 

392. What is dynamics? 

Ans. The science of moving powers. 

393. What is force? 

Ans. Th^t which alters the motion of a body, or puts 
in motion a body that was at rest. 

394. Define the maximum theoretical duty of steam? 
Ans, Mechanical equivalent of heat X total heat units 

in a pound of steam? 



Questions and Answers 461 

395. How may steam efficiency be expressed? 

Ans, Heat converted into useful work-^heat expended. 

396. How may engine efficiency be expressed? 

Ans. Heat converted into useful work-f-total heat re- 
ceived in the steam. 

397. How may efficiency of the plant be expressed? 
Ans, Heat converted into useful work-^calorific^ or heat 

value of the fuel. 

398. What is horse power constant? 

Ans. The power the engine would develop with one 
pound M. E. P. 

399. What is meant by steam consumption per H. P. 
per hour? 

Ans. Weight in pounds of steam used^H. P. developed ? 

400. What are ordinates as applied to indicator dia- 
grams ? 

Ans. Parallel lines drawn at equal distances across the 
face of the diagram, perpendicular to atmospheric line. 



The Indicator 

One of the greatest aids to the economical operation of 
the steam engine is the indicator^ and it is the privilege of 
every engineer to have at least an elementary, if not a 
thorough knowledge of its principles and working. The 
time devoted to the study of the indicator, and in its appli- 
cation to the engine, is time well spent, and in the end will 
well repay the student of steam engineering. 

Inventor. The indicator was invented, and first applied 
to the steam engine by James Watt, whose restless genius 
was not satisfied with a mere outside view of his engine as 
it was running, but he desired to know more about the 
action of the steam in the cylinder, its pressure at different 
portions of the stroke, the laws governing its expansion 
after being cut off, etc. Watt's indicator, although crude 
iu itb' design and construction, contained embodied within, 
it all of the principles of the modern instrument. 

Principles. These principles are: 

First. The pressure of the steam in the engine cylinder 
throughout an entire revolution, against a small piston in 
the cylinder of the indicator, which in turn is controlled 
or resisted in its movement by a spring of known tension, 
so as to confine the stroke of the indicator piston within a 
certain small limit. 

Second. The stroke of the indicator piston is communi- 
cated by a multiplying mechanism of levers and parallel 
motion to a pencil moving in a straight line. The distance 
through which the pencil moves being governed by the 

463 



464 Steam Engineering 

pressure in the engine cylinder and the tension of the 
spring. 

Third. By the intervention of a reducing mechanism 
and a strong cord^ the motion of the piston of the engine 
throughout an entire revokition is communicated to a small 
drum attached to, and forming a part of the indicator. The 
movement of the drum is rotative, and in a direction at 
right angles to the movement of the pencil. The forward 
stroke of the engine piston causes the drum to rotate through 
part of a revolution and at the same time a clock spring 
connected within the drum is wound up. On the return 
stroke the motion of the drum is reversed, and the tension 
of the spring returns the drum to its original position and 
also keeps the cord taut. 

To the outside of the drum a piece of blank paper of 
suitable size is attached and held in place by two clips. 
Upon this paper the pencil in its motion up and down 
traces a complete diagram of the pressures and other in- 
teresting events transpiring within the engine cylinder dur- 
ing the revolution of the engine. In fact the diagram 
traced upon the paper is the compound result of two con- 
current movements. First, that of the pencil caused by the 
pressure of the steam against the indicator piston; second, 
that of the paper drum caused by, and coincident with, the 
motion of the engine piston. The upper end of the indica- 
tor cylinder is always open to the atmosphere, the steam 
acting only upon the underside of the small piston, and 
when the cock connecting the cylinders of the engine and 
indicator is closed, both ends of the indicator cylinder are 
open to atmospheric pressure, and the pencil then stands 
at its neutral position. If now the pencil is held against 
the paper and the drum rotated either by hand or by con- 



TJie Indicator 



465 



necting it with the cord^ a horizontal line will be traced. 
This line is called the atmospheric line^ meaning the line 
of atmospheric pressure, and it is a very important factor 
in the study of the diagram. 




Fig. 161 
sectional view crosby indicator 



Figure 161 shows a sectional elevation of the Crosby 
indicator, and will give the student a good idea of its in- 
terior construction. Figure 162 shows the spring. 



466 Steam Engineering 

If the engine is a non-condensing engine the pencil in 
tracing the diagram will^, or at least;, should not fall below 
the atmospheric line at any point, bnt will on the return 
stroke trace a line called the line of back pressure at a dis- 
tance more or less above the atmospheric line and very 
nearly parallel with it. If the engine is a condensing en- 
gine the pencil will drop below the atmospheric line while 
tracing the line of back pressure on the diagram, and the 




Fig. 162 
crosby indicator spring 

distance this line is below the atmospheric line will depend 
upon the number of inches of vacuum in the condenser. 

As before stated, the length of stroke of the indicator 
piston, and the pencil movement as well is controlled by a 
spiral steel spring which acts in resistance to the pressure 
of the steam. These springs are made of different tensions 
in order to be suitable to different steam pressures and 
speeds, and are numbered 20, 40, 60, etc., the number 
meaning that a pressure per square inch in the engine 



Tlie Indicator 



467 



cylinder corresponding to the number on the spring will 
cause a vertical movement of the pencil through a distance 




Fig. 163 

improved tabor indicator with outside connected spring 

Ashcroft Mfg. Co., N. Y. 

of one inch. Thus, if a number 20 spring is used and the 
pressure in the cylinder at the commencement of the stroke 



468 Steam Engineering 

is 20 lbs. per square inch, the pencil will be raised one 
iiich^ or if the pressure is 30 lbs., the pencil will travel 1% 
in., and if there is a vacuum of 20 in. in the condenser, 
the pencil will drop i/^ in. below the atmospheric line for 
the reason that 20 in. of vacuum corresponds to a pressure 
of about 10 lbs. less than atmospheric pressure or an abso- 
lute pressure of about 4 lbs. If a 60 spring is used a pres- 
sure of 60 lbs. in the engine cylinder will be required to 
raise it one inch;, or 90 lbs. to raise it l^/^ inches. Figure 
163 shows the Tabor indicator, with outside connected 
spring. The spring is placed on top of the small cylinder, 
which arrangement removes it from the influence of the heat 
of the steam in the cylinder, and leaves it subject only to 
the temperature of the surrounding atmosphere. It is 
claimed that as a result of this, the accuracy of the spring 
is insured, and that no allowance need to be made in its 
manufacture for expansion caused by the high temperature 
to which it is subject when located within the cylinder. 
Another good feature of this design is, that the spring can 
be easily removed without disconnecting any one part of 
the instrument in case it is desired to change springs. 

Figure 164 shows a view of the American indicator with 
outside connected spring. 

The spring remains cool and can be changed without 
removing the piston or allowing the indicator to cool. It 
is in line with the piston, and is supported by two standards 
connected at the top by a cross bar, having a screw for at- 
taching the upper end of the spring. The lower end is 
connected to the top of the piston. The piston rod and 
connections are made hollow and as light as possible to pre- 
vent error from the inertia of the moving parts. 

To remove the spring, unscrew the nurled nut at the top 
until the end of the spring is released, and turn the spring 



Tlie Indicator 



46P 




Fig. 164 
american outside spring indicator 



470 Steam Rngineering 

until it is free from the base. To prevent the piston from 
turning while removing the springs insert a steel pin^ fur- 
nished with the indicator^ in holes in the spring base. 

Figure 165 shows the three-way cock for attaching the 
indicator to the cylinder of the engine. 

Reducing Mechanism. Probably the only practically 
universal mechanism for reducing the motion of the cross- 
head is the reducing wheel, a device in which, by the em- 
ployment of gears and pulleys of different diameters, the 




Fig. 165 

motion is reduced to within the compass of the drum, and 
the device is applicable to almost any make of engine, 
whether of high or low speed. Some makers of indicators 
attach the reducing wheel directly to the indicator, thus 
producing a neat and very convenient arrangement. 

Figure 166 illustrates a Crosby reducing wheel with the 
indicator mounted in place. The reducing motion is en- 
tirely distinct from the indicator, and terminates at the 
bottom with a swivel joint by ^'^hich it is attached to the 
indicator cock. On top, the arm of the reducing motion 



TTie Indicator 



471 



is finished to receive the swivel joint of the indicator itself, 
which is attached, as shown in the figure, in such a position 




Fig. 166 
crosby indicator and reducing motion assembled 

that the cord pulley of the indicator drum is directly over 
the small sheave about which the cord from the paper 
barrel is passed. Fig. 167 shows this position to better ad- 



472 



Steam Engineering 



vantage. The principal object sought and attained by 
this design and arrangement of reducing wheel and indi- 
cator is rigidity. As the wheel or its frame does not de- 
pend from the indicator proper^ the strength of the com- 
bination is good. The pull of the cross-head is resisted and 




Fig. 167 



the cord is returned by the helical spring A, Fig. 168, con- 
tained in the horizontal spring case B. Adjustment of this 
spring is made by the milled head which closes the outer 
end of the case and carries one end of the spring. This 
head slips over the squared end of the horizontal shaft D, 



TJie Indicator 



473 



and is secured in place by the thumb screw E. The shaft 
is carried on ball bearings P and G in the frame H^ and 




( 



Fig. 168 
sectional view of crosby reducing motion 



the web and gear I of the small sheave are a part of the 
liorizontal shaft. On this small sheave are the bushings J 



474 Steam Engineering 

which are taken ofi or added tO;, to get the proper ratio of 
motion for the paper drum. The bushings are held in place 
by a flange K^ and thumb screw L. 

The main frame H is a castings and from it depends the 
vertical shaft M^ upon which revolves the sleeve N carrying 
the smaller of the bevel gears and the cord-receiving sheave 
0. Beneath the large sheave and turning therewith is a 
screw engaging with the cross-head P which carries the 
cord guide Q. The cross-head is prevented from turning by 
two guide pins E and S^ upon which it slides^ and these 
pins are supported by a plate T at the bottom of the vertical 
shaft. This plate is secured by an hexagonal nut U. The 
arm carrying the cord guide is clamped around the cross- 
head;, and may be turned to lead in any direction. Above 
the bottom plate T is a stifl four-leaved spring V to receive 
the cross-head without shock in case it is allowed to run 
way down^, as it would by the breakage of the cord. 

When ready to use the reducing motion^ first mount the 
wheel frame on the indicator cock^, and the indicator on the 
frame^ as shown in Figs. 166 and 167. Then^, after deter- 
mining the size of bushing to go on the small sheave^ put 
it in place and secure it under the flange K with the nut L. 
Pass the cord from the paper drum once around the small 
sheave^ slipping the end through the hole in the flange and 
securing it to the cleat thereon. Be sure that there is 
enough cord on the large sheave to accommodate the long- 
est engine stroke for which the wheel will be used. Then 
pass the end through the guide pulley Q and there fasten 
it to resist the tension of the spring, leaving enough more 
cord to reach the cross-head of the engine. The cross-head 
P of the reducing motion must be just low enough for the 
guide pulley to lead the cord from the bottom flange of the 



The Indicator 



475 



large sheave, as shown in Fig. 166. Then the cord from the 
paper drum must be brought down and around the small 
sheave to the hole in the flange, so that while the motion 
is at rest, as in Fig. 166, it will pass around the sheave, in 
the direction of its travel, far enough to pass over the cir- 
cumference of the bushing on the sheave. Before fasten- 
ing to the cleat, the cord must be drawn taut, so that the 
paper drum will have just left its rest stop. 





Fig. 169 

To alter the tension on the recoil spring of this reducing 
motion, remove the nut E, and grasping the milled head 
C between the thumb and forefinger, pull it from the case 
far enough to allow it to be turned. Then twist it to the 
right, if more tension is desired, and allow it to slide onto 
the square end of the horizontal shaft again and replace the 
nut. To reduce the tension of the spring, allow the milled 
head to fall back to the left. 



476 



Steam Engineering 



If at any time the horizontal shaft D appears to be loose 
in its bearings and needs adjustment^ remove nut E^ grasp 
the head W in the fingers and back it off from its place. 
This will carry the spring, case and milled head from their 
positions and expose the adjustment X and its lock nut Y. 
Back off the lock nut and adjust the bearings with the other 
nut, after which lock the two nuts together again. Always 
try the bearings again after setting up on the lock nut. 




Fig. 170 

One of the most accurate and easily applied devices for 
reducing the motion of the piston is the wooden pendulum 
in its various forms. (See Figs. 169, 170 and 171.) It 
consists of a flat strip of pine or other light wood of a 
length not less than one and a half times the stroke of the 
engine, and if made longer it will be better. It should be 
from % to yg in. thick and have an average width of about 
4 in. If the engine to be indicated is horizontal the bar or 



The Indicator 



477 



pendulum is to be pivoted at a fixed point directly above^ and 
in line with the side of the crosshead, as that is generally 
the most convenient point of attachment. The pivot can 
be fixed to a permanent standard bolted to the frame of 
the engine^ or it may be secured to the ceiling of the room 
or even to a post fastened to the floor. If the engine is 
vertical the bar can be pivoted to the wall of the room, 
or a strong post firmly secured to the floor. The con- 




FiG. 171 

nection with the crosshead is best accomplished by means 
of a short bar or link. A convenient length for this bar is 
one-half the stroke of the engine. To locate the correct 
point for the pivot, assuming the length of the short bar 
to be one-half the length of the stroke, proceed as follows : 
Place the engine on the center with the crosshead at the 
lend of the stroke towards the crank. Then having pre- 
viously bored a hole for the pivot in one end of the pendu- 



478 



Steam Engineering 



lum bar, and in the other end a hole for connecting with 
the link, suspend the pendulum by a temporary pin, as a 
large wood screw, directly above and in line with the stud 
or bolt hole which has previously been tapped into the 
crosshead at any convenient point. The pendulum should 
be temporarily suspended at such a height that when it 
hangs perpendicular the hole in its lower end will line up 
accurately with the hole or stud in the crosshead. Now 
swing the pendulum in either direction a distance equal to 




Fig. 172 



the length of the link (one-half the stroke of the engine) 
from the crosshead connection and note the distance that 
the bottom hole is above a straight edge laid horizontal 
and in line with the center of" the stud in the crosshead. 
This will give the total vibration of the free end of the link 
from a line parallel with the line of the engine, and the 
permanent location of the pivot should be one-half of this 
distance below the temporary point of suspension. This 



Tlie Indicator 479 

will allow the link to vibrate equally above and below the 
center of its connection with the crosshead. Fig. 172 shows 
a complete connection of this character. 

Sometimes the end is slotted and thus directly connected 
.to the stud in the crosshead^ dispensing with the link. In 
this case it is necessary to locate the pivot at a point.per- 
pendicular to the center of travel of the stud in the cross- 
head. (See Fig. 169.) The link connection is to be pre- 
ferred, however. The cord can be attached to the pendulum 
at a point near the pivot which will give the desired length 
of diagram. This point can be determined by multiplying 
the length of the pendulum by the desired length of dia- 
gram and dividing the product by the stroke. For con- 
venience these terms should be expressed in inches. Thus, 
assume stroke of engine to be 48 in., length of pendulum 
1^/^ times length of stroke=72 in. Desired length of dia- 
gram 3 in. Then 72X3-^48=4.5 in., which is the distance 
from center of pivot to point of connection for the cord. 
This can be either a small hole bored through the pendulum, 
or a wood screw to which the cord can be attached. From 
this point the cord should be led over a guide pulley located 
at such height that when the pendulum is vertical the cord 
will leave it at right angles. After leaving the guide pulley 
the cord can be carried at any angle desired. One of the 
neatest and most easily applied devices for reducing the 
motion of the crosshead is the pantograph. (See Fig. 173.) 
No dimensions are essential except that it shall be made 
reasonably strong of some light, tough variety of wood, 
and that the pins and holes be nicely fitted to each other so 
that while the movement may be free there shall at the 
same time not be too much lost motion. The pantograph 
should be of such capacity that it will just close up nicely 



480 



Steam Engineering 



when the engine is at mid stroke and open out nicely when 
at its extreme travel. The two ends^ C and D^ are each to 
be fitted with a pin extending through far enough so that 
pin C can be hooked into a hole or socket on the crosshead^ 
while pin D rests in a socket in the top of a post secured 
to the floor at a point opposite the center of travel of the 
crossheacl^ and of such height as will allow the pantograph 
to lie in a horizontal position. Also the distance of the post 
from the guides must be adjusted so as to allow the device 




Fig. 173 



to close up at mid stroke^ and open out at full stroke with- 
out any straining of the parts. The point F of connection 
for the cord will always have a motion parallel with, and 
simultaneous with, that of the crosshead ; the pin to which 
the cord is attached can be set in any one of the holes that 
will give the desired length for the diagram. The motion 
given by this device is accurate, although it may become 
necessary in some cases, especially with long stroke engines, 
to introduce a guide pulley to carry the cord from the 
pantograph. 



The Indicator 481 

Attaching the Indicator, The cylinders of most engines 
at the present time are drilled and tapped for indicator 
connections before they leave the shop^ which is eminently 
proper, as no engine builder, or purchaser either, should 
be satisfied with the performance of a new engine until 
after it has been accurately tested and adjusted with the 
indicator. 

The main requirements in these connections are that the 
holes shall not be drilled near the bottom of the cylinder 
where water is likely to find its way into the pipes, neither 
should they be in a location where the inrush of steam 
from the ports will strike them directly, nor where the 
edge of the piston is liable to partly cover them when at 
its extreme travel. An engineer before he undertakes to 
indicate an engine should satisfy himself that all these 
requirements are fulfilled. Otherwise he is not likely to 
obtain a true diagram. The cock supplied with the indicator 
is threaded for one-half inch pipe, and unless the engine 
has a very long stroke it is the practice to bring the two 
end connections together at the side or top of the cylinder, 
and at or near the middle of its length, where they can be 
connected to a three way cock. The pipe connections 
should be as short and as free from elbows as possible in 
order that the steam may strike the indicator piston as 
nearly as possible at the same moment that it acts upon 
the engine piston. 

The work of taking diagrams is very much simplified 
by having both ends of the cylinder connected to one com- 
mon tee or a three way cock as above described, but for 
long stroke engines there should be two indicators, one for 
each end and the diagrams should be taken simultaneously 
if it IS desired to adjust the valves by the indicator. In 



482 Steam Engineering 

this case an assistant would be required to manipulate one 
of the instruments. 

The pipes should always be thoroughly blown out by 
allowing the steam to blow through the open cock during 
several revolutions of the engine^ before connecting the 
indicator. If this is not done there is a moral certainty 
that grit and dirt will get into the cylinder of the indicator^ 
where the presence of the least atom of grit will cause the 
delicate instrument to work badly. 

Selecting a Spring. The proper number of spring to 
use depends upon the boiler pressure in the case of an auto- 
matic cut off engine^ but for an engine with a fixed cut off 
and throttling governor the number of the spring to be 
selected will depend upon the initial pressure in the cylinder. 
A convenient rule is to select a spring numbered one-half 
as high as the pressure ; for instance^ if the boiler pressure 
is 80 Ibs.^ use a ISTo. 40 springy which will give a diagram 
2 in. in height. 

Care of the Instrument. The indicator should be cleaned 
and oiled both before and after using. The best material 
for wiping it is a clean piece of old soft muslin of fine 
texture^, as there is not so much liability of lint sticking to 
or getting into the small joints. Use good clock oil for the 
joints and springs^ and before taking diagrams it is a good 
practice to rub a small portion of cylinder oil on the piston 
and the inside of the cylinder^ but when about to put the 
instrument away these should be oiled with clock oil also. 
I^one but the best cord should be used for connecting the 
paper drum with the reducing motion^ as a cord that is 
liable to stretch will cause trouble. Suitable cord and also 
blank diagrams can generally be secured from firms manu- 
facturing and selling indicators. After the indicator has 



TTie Indicator 483 

been screwed on to the cock connecting with the pipe, the 
cord must be adjusted to the proper length before hooking 
it on to the drum. This must be done while the engine is 
Tunning, by taking hold of the loop on the cord connected 
with the reducing motion with one hand, and with the 
other hand grasp the hook on the short cord attached to 
the drum, then by holding the two ends near each other 
during a revolution or two it will be seen whether the long 
cord needs to be shortened or lengthened. 

The length of the diagram is determined by the point 
of connection of the cord to the pendulum as has been 
heretofore explained. Care should be exercised in placing 
the paper on the drum, to see that it is stretched tight and 
firmly held by the clips. The pencil point having been 
first sharpened by rubbing it on a piece of fine emery cloth 
or sand paper should be adjusted by means of the pencil 
stop with which all indicators should be provided, so that 
it will have just sufficient bearing against the paper to 
make a fine, plain mark. If the pencil bears too hard on 
the paper it will cause unnecessary friction and the diagram 
will be distorted. The best method of ascertaining this fact 
and also whether the travel of the drum is equally divided 
between the stops, is to place a blank diagram on the drum, 
connect the cord and while the engine makes a revolution 
hold the pencil against the paper. Then unhook the cord, 
remove the paper and if the travel of the drum is not di- 
vided correctly it can be changed. 

Having thus arranged all the preliminary details, place 
a fresh blank on the drum, being careful to keep the pencil 
out of contact with it, connect the cord, open the cock ad- 
mitting steam to the indicator and after the pencil has 
made a few strokes to allow the cylinder to become warmed 



484 Steam Engineering 

up, then gently swing it around to the paper drum and 
hold it there while the engine makes a complete revolution. 
Then move the pencil clear of the paper, close the cock 
and unhook the cord. N"ow trace the atmospheric line by 
holding the pencil against the paper while the drum is 
revolved by hand. This method of tracing the atmospheric 
line is preferable to that of tracing it immediately after 
closing the cock and while the drum is still being moved 
by the engine, for the reason that there is not so much 
liability of getting the atmospheric line too high owing to 
the presence of a slight pressure of steam remaining under 
the indicator piston for a second or two just after closing 
the cock; also the line drawn by hand will be longer than 
one drawn while the drum is moved by the motion of the 
engine, and will therefore be more readily distinguished 
from the line of back pressure. 

Having secured a truthful diagram, it now remains to 
take as many as are desired, and if the object is to set the 
valves of the engine, the diagrams from each end of the 
cylinder should follow each other as quickly as possible in 
order that the conditions of load and steam pressure may 
be the same. When the indicator is connected so that dia- 
grams can be taken from both ends without changing it, 
the above conditions can generally be realized. But if 
diagrams can only be taken from one end at a time, the 
only way to arrive at correct conclusions in relation to the 
adjustment of the valves will be to see that the boiler pres- 
sure is practically the same at the time of taking diagrams 
from either end and that the position of the governor is 
also the same, assuming that the load on the engine is 
practically constant. This applies of course to an auto- 
matic cut off. 



Tlie Indicator 485 

[»> As soon as the diagrams are taken the following data 
should be noted upon them: The end of the cylinder, 
whether head or crank; boiler pressure; and time when 
taken. Other data can be added afterwards. If the engine 
is an automatic cut off of the Corliss type, and the point of 
cut off on one end does not coincide with the other, the 
difference can generally be adjusted while the engine is 
running by changing the length of the rods extending 
from the governor to the tripping device. These rods are, 
or should be, fitted with right and left threads on the ends 
for this purpose. Any changes in the valves, such as giv- 
ing them more lead, compression, etc., and which neces- 
sitates changing the length of the reach rods connecting 
them with the wrist plate, will have to be made while the 
engine is stopped, although with slow speed engines and 
the exercise of caution it is possible to make alterations in 
these rods while the engine is running. 

DIAGRAM ANALYSIS. 

Before proceeding to the study of indicator diagrams, it 
is well to define the different points, lines and curves of a 




Fig. 174 

diagram in order that the young student may get these 
matters firmly fixed in his mind, and that there may be 
no confusion. 



486 Steam Engineering 

Eef erring to Fig. 174^ from C to B is the compression 
curve^ which in this particular diagram is somewhat lighter 
than is ordinarily given to engines. This is due to the fact 
that the engine from which Fig. 174 was taken is of slow 
speed and long stroke, and therefore does not require as 
heavy a cushion as does a high speed, short stroke engine. 

From B to D is the admission line, which being practi- 
cally perpendicular to the atmospheric line A, shows suffi- 
cient lead and ample port area. From D to E is the steam 
line. Cut ofi occurs at E, and from E to F is the expansion 
curve. At F the point of release is quite sharply defined, 
as it should be. From F to G is the exhaust line, and from 
G to C the line of back pressure, sometimes called the line 
of counter pressure for the reason that the pressure indi- 
cated by it acts counter or in opposition to the forward 
pressure of the steam on the piston. This engine is a 
simple condensing engine, and the nearness of the back 
pressure line to the line of perfect vacuum V shows that an 
excellent vacuum was maintained in the condenser. 

It should be noted that all of the diagrams referred to 
in the following pages are reproductions of actual diagrams 
taken under ordinary working conditions. Figs. 175, 176 
and 177 are reproductions of diagrams taken from a Cooper 
Corliss non condensing engine. 

The dimensions of the engine are as follows : Diametei 
of piston, 34 in. ; length of stroke, 42 in. 

At the time Fig. 175 was taken the boiler pressure was 
105 lbs., but it was increased a few months later to 110 lbs., 
as was the load also, when Figs. 176 and 177 were taken. 

These diagrams are fairly good working cards, but there 
are some defects which it might be well to point out. 

Eef erring to Fig. 175, it will be noticed that the initial 
pressure at s, on the head end, is 94 lbs., while on the crank 



Diagram Analysis 



487 



end the initial pressure runs up to 99 lbs. above the atmos- 
1 pheric line. 



CCcCf''P(^iAyL>t^?'i^ 




Fig. 175 

This decrepancy is caused by insufficient lead on the 
head end, plainly shown by the inclination inward of the 
admission line, and the rounded corner at s. 



488 



Steam Engineering 



The compression is excessive, especially on the head end, 
as indicated by the curve at L. 



CZcC^t^t'tyty^'^^o 




< \ 



Fig. 176 



These two factors, lead and compression, may always be 
distinguished by observing the character of the admission 
line. 



Diagram Analysis 



489 







Fig. 177 



A curve, such as shown at L, denotes too early closure 
of the exhaust, and the rounded corner at ?, and inward 



490 Steam Engineering 

inclination of the admission line from 1 to s is a pretty sure 
indication that the steam lead is not snfScient. 

The diagram from the crank end is much better^ although 
there is more compression than is needed. 

The cut-off is not equalized^ that on the crank end takes 
place earlier in the stroke than the same event does on the 
head end^ and the consequence is that the M. E. P. for the 
head end is 60.4 lbs. while the M. E. P. for the crank end 
is 54.4 lbs. (see Fig. 177), a difference of 6 lbs. more 
pressure per square inch being exerted against the piston 
as it travels from the head end of the cylinder, than there 
is exerted against it as it travels from the crank end, and 
this unequal strain, or push is felt by the moving parts 
of the engine 160 times a minute, the engine making 80 
E. P. M. 

It is unnecessary to again emphasize the need of care 
and good judgment in the adjtistment and equalizing of the 
points of cut off. On an engine, a very simple calculation 
will be sufficient. 

The diameter of the piston under consideration is 34 in., 
area 907.92 sq. in., pressure per sq. in. 6 lbs. Then 907.92 
X 6=5447.52 lbs., which divided by 2,000=2.72 tons more 
pressure against the piston when traveling from the head 
end, than there is on the return stroke. 

Figure 176 is a much better appearing diagram, the lead 
on the head end having been slightly increased, thus practi- 
cally equalizing the initial pressure, and improving the 
rounded corner at s. 

The variation in the points of cut off at c. 0. still exists, 
and the compression is still too great. 

As before stated, the three diagrams shown are all from 
the same engine and figure 17 7. is introduced for the pur- 



Diagram Analysis 491 

pose of illustrating the method of obtaining the M. E. P. 
by the use of ordinates, as they are termed^ they being the 
vertical lines, drawn in order to facilitate the measurement 
of the pressures shown by the steam line, and expansion 
curve above the line of atmospheric pressure, or if the en- 
gine is a condensing engine these measurements must be 
made from the vacuum line, as drawn by the indicator 
pencil. 

The first requisite in this process is to correctly draw 
these ordinates, spacing them equidistant apart. 

First draw lines 1 and 2 at each end of the diagram, and 
perpendicular to the atmospheric line. 

Then measure the distance between these two lines, and 
this distance, whatever it may be, should be divided into 
ten equal spaces, although it is not absolutely necessary 
that there should be ten spaces, as any other number of 
spaces will serve, provided they are of equal width. 

Ten is usually chosen, owing to the fact that this num- 
ber is the most convenient to use in calculations. 

In Fig. 177 the distance across the face of the diagram 
from line 1 to line 2 is found to be nearly 3{f in. or 63 
sixteenths, which divided by 10 equals a little more than 6 
sixteenths or % in. 

Therefore the width of the spaces will be % in. and the 
vertical lines should be drawn that distance apart. 

Having drawn the lines, the next step is to measure the 
pressure by using the scale corresponding to the spring 
that was used. These different scales 40, 50, 60, 80, etc. 
are supplied by the makers of the indicator, and should ac- 
company each outfit. 

Again referring to Fig. 177, beginning at the head end, 
lay the scale along the middle of the first space witli the 



492 Steam Engineering 

zero mark on the compression curve^ and the pressure from 
c to s is found to be 64 lbs. 

This is the effective pressure exerted against the piston 
at this point in the stroke notwithstanding the fact that the 
boiler pressure was 110 lbs. 

Eight here the quer}' might arise^ why this decrease in 
pressure ? and it might be well to explain the cause of it. 

The actual work area of the diagram is only that portion 
confined within its own boundary lines as traced by the 
pencil when in motion. The lines of atmospheric pressure, 
and vacuum are traced by hand^ and their purpose is to 
facilitate measurements only. 

Therefore the pressure can only be measured from points 
c and s in the two spaces at the beginning of the stroke. 

It is evident therefore that too much compression, or too 
much lead tends to lessen the work area of the diagram at 
the beginning of the stroke, thus placing a limit on the 
capacity of the engine for doing work. 

Measurements for pressure on the remaining spaces of 
Fig. 177 may be made from the atmospheric line, except 
that when measuring the diagrams from the crank end the 
same rule governs the measurement of the pressure in the 
space at the beginning of the stroke, viz., measure from the 
compression curve, c, to the steam line s. The pressure in 
this case is found to be 67 lbs. 

In space two (crank end) the, pressure measured from 
the atmospheric line is found to be 96 lbs., and on the head 
end it is 95 lbs. 

After all the ten spaces have been measured, say from 
the head end, and the results added together, it is found 
that the total is 604, which divided by 10 equals 60.4 lbs., 
which is the M. E. P. for that end. 



Diagram Analysis 493 

Proceeding in the same manner with the crank end the 
M. E. P. is found to be 54.4 lbs. 

The cause of this difference of 6 lbs. between the two 
diagrams^ and its effect upon the engine has already been 
explained. 

In order to obtain the average M. E. P. it is necessary to 
add the two results together and divide the sum by 2, thus : 
60.4+54.4-f-2=57.4 lbs. 

Before proceeding to calculate the H. P. there is another 
factor to be considered^ viz.^ the back pressure^, which is 
always present in a greater or less degree^ and which in 
Fig. 177 is found to be 4 lbs.; ascertained by measuring 
with the scale the distance from the atmospheric line to 
the line of back pressure, B. P. 

This 4 lbs. is to be deducted from the average M. E. P.; 
thus 57.4 — 4=53.4 lbs., which is the net pressure for power 
calculations. 

It should be noted that the number of the spring used 
on Fig. 177 was 60. 

The process of ascertaining the M. E. P. by ordinates, 
jnd also by the use of the planimeter will be enlarged upon 
later on in this discussion. 

Great care should be exercised in these calculations, es- 
pecially in taking measurements of the pressure by the use 
of ordinates, on diagrams taken from engines using steam 
of high initial pressure, 150 to 250 lbs. per sq. in., where 
springs of high tension (80 to 125 lbs.) are required. 

The lines on such scales are so close together, and the 
figures are so small, that it is very difficult to distinguish 
them. However, there are other and more simple methods 
that can be used, and the results are just as accurate. 



494 



Steam Engineering 



Figures 178 and 179 are reproductions of diagrams 
taken from a 14x30 in. engine^ and are introduced for the 
purpose of showing the need of care and good judgment 
in the selection of a spring. 




A 



Fig. 178 




Fig. 179 



-J/T 



The boiler pressure at the time the cards were taken was 
90 lbs. per sq. in. but a 60 spring was used^ when a much 
better diagram might have been secured with a 50 spring. 



Diagram Analysis 495 

The fluctuations in the steam lines S to C are caused 
by the spring being of too high tension^ and they are brought 
about in the following manner. 

Initial pressure is high enough at the beginning of the 
stroke to run the admission line up to 82 lbs. on the head 
end of Fig. 178 and to 78 lbs. on the crank end^ but the high 
tension of the 60 spring immediately causes the indicator 
piston to drop slightly^ and remain so until about l-12th 
of the stroke is completed^ when the steam pressure slowly 
overcomes the tension of the springs and the pencil again 
slowly rises^ and remains steady until cut ofE occurs. 

The same defect appears in Pig. 179 taken from this 
engine running with a somewhat lighter load. 

The engine is 14x30 in. running at a speed of 100 E. P. 
M. The exhaust steam passes through heating coils in a 
dry kiln^ which accounts for the high back pressure lines 
on the diagrams. 

Aside from the above mentioned defects the diagrams 
are good. The valves appear to be properly adjusted for 
compression, lead;, and cut off^ these events all occurring in 
their regular order. 

Unequal cut of. The unequal division of forces^ or 
pressures acting alternately upon the piston of a steam en- 
ginC;, to propel it back and forth, may be likened, in a 
measure, to two men working a ratchet drill, or pumping 
a hand car. 

If one of the men is a small, weak man and his partner 
is a big strong-armed man, the result will be that the big 
man will do most of the work, even though the small man 
may be willing enough, and does all that he is able to do. 

With an engine, this unequal division of pressures, in 
other words, unequal cut off, may be easily remedied through 
the instrumentality of the indicator. 



496 



Steam Engineering 



The bad effects of unequal cut off will make themselves 
felt^ and heard also in time. The engine will not develop 
the power that it is capable of developing, the coal con- 
sumption per H. P. per hour will be greater than it should 
be, and it will be a much harder task to keep the engine 
running smoothly under such conditions than it would be 
if the cut off was equalized, and the mean effective pres- 
sures were the same or nearly so for each stroke. 




Fig. 180 



Figure 180 is a reproduction of a diagram taken from a 
Corliss engine 30 in. bore by 48 in. stroke, running 82 
E. P. M. 

One of the minor defects of the diagram is that it occu- 
pies too much space, meaning that it is too high, and too 
long. The fault in height is cau"feed by using too light a 
spring in the indicator, allowing the indicator piston to 
rise too high. 

The boiler pressure at the time the cards were taken was 
120 lbs., but the spring used was a 50 lbs. spring, when it 
should have been a 60 lb. 



Diagram Analysis 497 

The springs or scale as it is often designated, should be 
selected in accordance with the boiler, or gauge pressure. 

For instance, if the gauge pressure is 120 lbs. a 60 spring 
should be used. If the gauge pressure is 90 or 100 lbs. 
a 50 spring is strong enough. 

A good rule to observe in this matter is, to use a spring, 
or scale of as nearly one-half the gauge pressure as it is 
possible to get it. 

The diagram will then be about 1% in. in height, which 
is much more easily measured than one that is two inches 
in height, such as Fdg. 180 shows. 

Of course it must be understood that these measure- 
ments are to be made from the atmospheric line A. 

The cause of the excessive length of the diagram is too 
long a stroke of the reducing motion. This is easily 
remedied also. 

A convenient length for a diagram is from two to two 
and a half inches. 

The lead and compression lines shown at 1-1, Fig. 180, 
are practically perfect. It is plain from these lines that 
lead begins where compression lets go, which is as it should 
be. 

The admission lines 1 to 2 on both crank and head ends 
are good also, and indicate prompt opening of the steam 
ports. 

The release at R' also shows good economy^ and there is 
practically no back pressure on the piston for either stroke. 

But here is where our favorable criticism of Fig. 180 
ends, except that we might say with reference to the ex- 
pansion curve, 3 to E', of the crank end diagram, that it 
compares favorably with the • theoretical expansion curve. 

The main trouble with the engine, as shown by the dia- 



498 Steam Engineering 

gram is unequal cut off^ that on the head end being con- 
siderably later in the stroke than it should be^ while cut off 
on the crank end occurs a little too soon. 

This is also shown by measurement of the mean effective 
pressures^ that on the crank end being 42.1 pounds while 
that from the head end is 48.2 pounds, showing that there 
is 48.2 minus 42.1 equals 6.1 pounds more M. E. P. on the 
head end than on the crank end. 

This means that the piston which is 30 inches in di- 
ameter having an area of 706.86 square inches has 706. 86x 
6.1 equals 4311.84 pounds more pressure exerted against 




Fig. 181 

its surface during the stroke from the head of the cylinder 
than it has on the opposite stroke. 

It also means that the strains are unequally divided so 
far as regards the moving parts of the engine. The en- 
gineer in charge reports that he has lots of trouble with his 
engine in his efforts to keep it running quietly, but this is 
to be expected considering the unequal cut offs, and the dif- 
ference in the pressures upon the piston at each stroke. 

The H. P. developed by the engine as indicated by Fig. 
180 is 564.8. 



Diagram Analysis 



490 



'Effects of Wire Drawing. Fig. 181 is from a Buckeye 
automa.tic cut off engine having a shaft governor and^ what 
is termed a riding cut off^, that is the cut off valve slides to 
and fro on the back of the main valve. The engine is hor- 
izontal non-condensing^ the cylinder being 28 in. bore by 
56 in. stroke^ and, at the time the diagram Avas taken, de- 
veloped 357.58 horse power with a piston speed of 728 ft. 
per minute. The steam consumption per I. H. P. per hour 
was 26 pounds, a rather high rate, but this was owing to 
the fact that the engine Avas located too far from the boil- 
ers, and as there were a large number of elbows in the steam 




Fig. 182 



pipe the pressure was greatly reduced at the engine. Thus 
wire drawing of the steam was caused, which is plainly in- 
dicated by the downward inclination of the steam line, J) E. 

In a well proportioned engine having a steam pipe of 
sufficiently large area, the steam line should parallel the 
atmospheric line up to the point of cut off. Fig. 181 in- 
dicates proper release of the steam at F, and the back pres- 
sure from G to C, which is 3 pounds above the atmospheric 
line, shows a reasonably free passage of the exhaust steam. 

Figs. 182 to 187 illustrate diagrams from three new ver- 
tical Corliss engines supplying power for an electric light- 
ing plant, which the author was requested to test and ad- 



500 



Steam Engineering 



just after they had been in operation a few months. The 
valves had previously been set by the erecting engineer at 
the time the engioes were set up. Each one of these en- 
gines exhausted into a separate condenser of the Jet type, 
into which the condensing water was forced under pressure, 
and from which the overflow was discharged by gravity 
into a sewer. There was no air pump and as a consequence 
the vacuum maintained was very low^ usually from 10 to 
15 in., and at times still less, so that the beneficial results 
of condensing were only partialh^ realized. 




Fig. 1S3 



For convenience the diagrams from each engine will be 
treated in numerical order, beginning with engine No. 1. 
This engine was 24x48 inches, running 70 E. P. M., with 
a boiler pressure of 68 pounds. A 40 spring was used in 
the indicator. The principal defect was the lack of suffi- 
cient lead on both ends, as indicated by the inclination in- 
ward of the admission lines and the rounded corners of the 
steam lines at the beginning of the stroke. (See Fig. 182.) 
There was also more compression, especially on the bottom 
end, than was necessary, considering the size of the engine, 
and the speed. The necessary changes having been made, 
the indicator was again applied and the diagram, Fig. 183, 



Diagram Analysis 501 

was obtained, which shows the distribution of the steam to 
be satisfactor}^, although at the time of taking this di- 
agram the boiler pressure was only 60 pounds, while it 
should have been 68 or 70 pounds, because with the latter 
pressure still better results could have been attained. The 
I. H. P. was 235 and the steam used per I. H. P. per hour 
was 18 pounds. 

Fig. 184 is the original diagram froni engine No. 2, and 
shows bad valve adjustment all around, with the exception 
of lead on the top end. The variation in the points of 
cut off is the worst feature; cut off taking place on the 
bottom at 29 per cent, of the stroke, while on the top end 




Fig. 184 

it does not occur until the piston has traveled through 42 
per cent, of the stroke. There is more compression, also 
than is needed. This engine was 18x42 inches, running 
at a speed of 78 E. P. M., and the steam consumption, ac- 
cording to diagram Fig. 184, was 33 lbs. per I. H. P. per 
hour. Having equalized the cut off and reduced the com- 
pression by making the necessary changes in the valve gear, 
the indicator was again applied, resulting in diagram Fig. 
185, which may be considered practically perfect. The 
boiler pressure was 68 pounds and the spring used was a 
No. 40. The steam consumption was reduced to 22 pounds 
per I. H. P. per hour as compared to 33 lbs. in Fig. 184. 



502 



Steam Engineering 



Figs. 186 and 187 represent diagrams from engine 'Eo. 
3, which was the same size as No. 1^ viz._, 24x48 in., and 
running at 72 E. P. M. The original diagram. Fig. 186, 
shows too little lead on both ends, but especially on the top. 
There is also lack of compression on the bottom end. The 




Fig. 185 

boiler pressure was 60 pounds, and the scale of spring 40. 
Fig. 187, taken after the necessary adjustments had been 
made, shows much better valve performance. The horse 
power developed was 251 and the steam consumption was 
20.5 pounds per I. H. P. per hour. The rather high rate 




Fig. 186 

of steam consumption for this engine as compared with 
engine No. 1, which was the same size but consumed only 
18 pounds of steam per I. H. P. per hour, was due to two 
causes. First, a low vacuum; second, low initial pressure 
necessitating a late cut oS. 



Diagram Analysis 



503 



Pigs. -188 to 191 are reproductions of diagrams taken 
from a new horizontal non-condensing engine which had 
been running about eight or nine months when it fell to 
the author^s lot to apply the indicator to the engine, not 
only for the purpose of adjusting the valve motion, but 




Fig. 187 



also to make a series of tests for the purpose of ascertaining 
the amount of power delivered by the engine to each one of 
several different departments which were receiving power 
from this source. 




Fig. 188 

The dimensions of the engine were as follows: bore of 
cylinder, 32 in.; stroke, 5 ft. At the time Fig. 188 was 
taken the engine was making 62 E. P. M. and the boiler 
pressure was only 50 pounds. A 30 spring was used. 
Although the load on the engine was very light at the time. 



504 



Steam Engineering 



3^et the diagram served as a guide to some extent in set- 
ting the valves, and by taking off the bonnets from the 
valve chests and making the necessary changes in the ad- 
justment by the marks on the valves a pretty fair job was 




Fig. 189 



made of it, as will be seen by referring to Fig. 189. The 
reducing motion was a pantograph, and as it is very easy 
to vary the travel of the paper drum with this motion^ 
diagrams of different lengths were taken until the one which 




Fig. 190 



appeared to be the most satisfactory was obtained. The 
slight hump in the expansion curve immediately after cut 
off, was probably caused by a speck of dirt or grit which 
momentarily checked the indicator piston on the down 



Diagram Analysis 



505 



stroke. The compression on the crank end is not sufficient 
and the exhaust valve rod on that end was slightly length- 
ened^ resulting in the production of diagram Fig. v 190. In 
this diagram the familiar hump in the crank end expan- 
sion curve reappears, but in a different location, being 
nearer the end of the stroke. It will also be noticed that 
the length of Fig. 190 has been considerably reduced from 
that of Fig. 188, it being about one inch shorter. 



Hs^i^ 




Fig. 191 



The boiler pressure and the load on this eng were 
gradually increased from time to time, from 50 pounds, 
and a light load (as shown by Fig. 188) to 60 pounds and 
335 horse power (as indicated by Fig. 189 taken some three 
months later), and when Fig. 191 was taken, about two 
years and eight months later, the boiler pressure had been 
increased to 87 pounds and the I. H. P. was over 700. 

Diagram Fig. 191 shows good economy in the use of 
steam in spite of the fact that the cut off occurs rather late. 



506 



Steam Engineering 



There is no back pressure worth mentioning, the back pres- 
sure line forming part of the atmospheric line through the 
largest p^rt of the stroke. The reason for this is that the 
areas of the exhaust ports, as well as the exhaust pipe were 
sufficiently large to permit a free passage for the steam. 
The exhaust pipe, also, was made as short and direct as 
possible and all superfluous elbows were dispensed with. 
The steam consumed per I. H. P. per hour as per diagram 
Pig. 191 was 22.3 pounds, and the horse power developed 
was 710.6. 




Fig. 192 



Pigs. 192 to 194, inclusive, represent diagrams from a 
Buckeye engine 24x48 inches, and are introduced for the 
purpose of emphasizing the need of caution and good judg- 
ment in setting valves by the indicator when the load on 
the engine is variable. Pig. 192, which was the first to be 
taken, would seem to indicate that the valve was badly ad- 
justed, but when Pig. 193 was taken immediately after- 
wards, the cause of the trouble became apparent. The 
engine was furnishing power for operating an electric street 



Diagram Analysis 



J07 



railway on a small scale, and the variation in the points 
of cut off was caused by the stopping and starting of the 



cars. 



Fig. 193 is a notable example of the quick and delicate 
action of the shaft governor, as it will be seen that during 
four successive revolutions there was a different load each 
tim.e, as shown by the diagram from the crank end. 





\ 




^ 


\ 


h 




/^ 






^ 


^^ 


^ 


\ 






^ 


. ^ 










1 






\ 


I 






^. 










1 


^ 


N^ 




\ 


^^^^ 


"'^'^ 


^ 


^ 






~-«^il 


15. 


1^ 




V^ 


^"^"^ 






^ 






^ 


s. 


Ui 




/ 


V 














L> 


^ 


5r 


J^ 


•0 










^ 


•«» 


l\ ^ cv 






N> 


V*, 


SS. 


*»** 


"^ 


•^ 


v> 


K> V4 V. 




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o 


Cx> 


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Fig. 198 

Fig. 194 was secured by quick manipulation of the in- 
strument when it was known that the load was to be steady 
for a few seconds. 

Fig. 195 is from an Atlas single valve automatic cut off 
engine with shaft governor. This engine was 16x24 
inches, running at 105 E. P. M., and at the time the di- 
agram was taken the boiler pressure was only 50 pounds. 
The spring used was a No. 30. The diagram is a fairly 
good one for the type of engine. Owing to the variation 



508 



Steam Engineering 



in the angular advance of the single eccentric actuated by 
a shaft governor, the degree of compression varies with the 
point of cut off in the single valve engine, the compression 




Fig. 194 

being higher with an early cut off' than it is when cut off 
occurs later in the stroke. The loop at A is caused by too 




Fig. 195 



much lead which, together with the compression, caused a 
momentary rise in the pressure above the normal. The 
lead at B is approximately correct. The difference in ter- 



Diagram Analysis 



509 



minal pressures at C and D is the result of shifting of the 
points of cut oif caused by variations in the load. The 
back pressure lines are almost identical with the atmos- 







Fig. 196 

pheric line^ showing that the exhaust is in no way restricted 
or cramped. I. H. P. is 65.7 and steam consumption 21 
pounds per I. H. P. per hour. 




Fig. 197 

Figs. 196 and 197 are diagrams taken from a cross com- 
pound condensing Corliss engine. The high pressure cylin- 
der was 24x48 inches^ and the low pressure cylinder was 
44x48 in. The steam from the high pressure exhausted 



510 Steam Engineering 

into a receiver^ and from tbence into the low pressure cylin- 
der. The receiver pressure was 5.3 pounds above atmos- 
pheric pressure. The ratio of piston areas was 3.36 to 1. 
That is, the area of the low pressure piston was 3.36 times 
the area of the high pressure piston, which was about the 
correct ratio for the pressure carried, viz., 84 pounds gauge 
or 99 pounds absolute. A No. 40 spring was used on the 
high pressure and a No. 12 on the low pressure cylinder. 
The number of expansions in the two cylinders was 14. 
Thus, the ratio of expansion in the high pressure cylin- 
der was 4.5 and in the low pressure the ratio was 3.1. 
Then 4.5X3.1=14; or. Thus, initial pressure=99 pounds 
absolute, terminal pressure in L. P. cylinders? pounds 
absolute; then 99^7=14. 

To illustrate the process of finding the M. E. P. without 
the use of ordinates when the absolute initial and terminal 
pressures and the number of expansions in each cylinder 
are known, the following problems will be worked out : 

Find M. E. P. in L. P. cylinder. 

First, find initial pressure. 

Rule. T. P. multipled by number of expansions. Thus, 
7X3.1=21.7 pounds absolute initial pressure in L. P. 
•cylinder. 

Second, find mean forward pressure (M. F. P.). 

Bule. Multiply initial pressure by hyperbolic logarithm 

of number of expansions plus 1, and divide product by num- 

l)er of expansions. Thus the hyperbolic logarithm of 3.1 

21.7X^.1314 

=1.1314, to which add 1=2.1314. Then = 

3.1 

14.9 pounds M. F. P. Deduct from this the back pressure, 

which was 5 pounds absolute. Thus, 14.9 — 5=9.9 pounds 

M. E. P. in L. P. cylinder. 



Diagram Analysis 511 

Next find M. E. P. in H. P. cylinder. 

First, find T. P. in H. P. cylinder. 

This will equal the initial pressure in the L. P. cylinder 
4-2 per cent, for loss in the receiver. Thus, 21.7+.4=i 
22.1 pounds, terminal pressure in H. P. cylinder. 

Second, find initial pressure in H. P. cylinder. 

Rule, Multiply T. P. by number of expansions. Thus^ 
22. 1*X 4.5=99.4 pounds absolute initial pressure in H. P. 
cylinder. 

Third, find mean forward pressure (M. F. P.). 

The hyperbolic logarithm of 4.5=1.5041, add 1=2.5041. 

99.4X2.5041 
Then =55 pounds, M. F. P. in H. P. cylin- 
der. Deduct back pressure 22.1; thus, 55 pounds — 22.1 
pounds=32.9 pounds, M. E. P. in H. P. cylinder. 

The ratio of piston areas being 3.36 to 1, it may be of 
interest to pursue the subject a little farther and ascertain 
how the distribution of the steam in the two cylinders cor- 
responds to the ratio of areas. The ratio and pressures 
may be expressed as follows : 

Eatio of areas — H. P. cylinder, 1; L. P. cylinder, 3.36. 
M. E. P.— H. P. cylinder, 32.9 ; L. P. cylinder, 9.9 pounds 
which is very nearly correct ; sufficientl;f so for all practical 
purposes, and clearly demonstrates that with the intelligent 
use of the indicator it is possible to so adjust the valves, 
and establish the points of cut off on a compound, or triple 
expansion engine, that the work done in each cylinder will 
be practically the same. As for instance, the product of 
the area of the H. P. piston and the M. E. P.= 14,883.6 
pounds, and that of the L. E. piston X M. E. P.= 15,052.9 
pounds, a difference of only 169.3 pounds. If the two pro- 
ducts had been equal, the horse power exerted in the two 



512 



Steam Engineering 



cylinders would have been the same. As it was^ the horse 
power of the H. P. cylinder was 263.4 and that of the L. P. 
cjdinder was 266.4^ showing a difference of only three horse 
power in the amount of work done in each cylinder. 

Fig. 198 was taken from one of a pair of Fishkill Cor- 
liss engines connected to a common crank shaft. The en- 
gines were each 24x48 inches^ and run at 65 E. P. M., with 
a boiler pressure of 65 pounds. They were equipped with 
a jet condenser, and a bucket plunger air pump served for 
both engines. These engines had been in continuous 
service for nearly seventeen years when the author was 




Fig. 198 



called upon to indicate them and adjust the valves. A 
diagram taken at the same time from the mate of this en- 
gine was very nearly an exact counterpart of Fig. 198. 
The horse power, as shown by Fig. 198, was 248, and the 
steam per I. H. P. per hour was 15.2 pounds. The vacuum 
gauge showed 27 inches and a 50 spring was used. 

Figs. 199 and 200 are from an old Fishkill Corliss en- 
gine 16X42 inches, to which the author applied the indi- 
cator, after he had set the valves, according to the ordin- 
ary rules for valve setting, by the marks placed on the ends 
of the valves and valve chests. These diagrams are in- 
troduced especially for the purpose of showing the need of 



Diagram Analysis 



513 



exercising the greatest of care to prevent dirt or grit of 
any kind from getting into the indicator cylinder. After 
the indicator pipes had been blown out sufficiently^ as it 
was thought;, the indicator^ which was a thoroughly reli- 
able instrument^ was attached and diagram Fig. 199 was 




Fig. 199 



obtained. It showed the valve adjustment to be very 
nearly correct, but the perfectly straight steam lines, and 
the sharp corners and sudden drop at cut off were a puzzle, 
especially in an old engine where the valves and valve seats 




Fig. 200 



were known to be much worn down. After taking several 
more diagrams with precisely the same result, the indicator 
was removed, and upon taking out the piston a quantity of 
dirt was found on it, and also on the inside of the cylinder. 
This fully explained the cause of the sharp corners, etc., 



514 Steam Engineering 

on the diagram. After the indicator had been cleaned and 
oiled it was again connected;, and Pig. 200 was produced, 
which is a truthful presentation of the performance of the 
steam in the cylinder. 

Many diagrams are misleading^, owing to causes similar 
to the above^ and a diagram with too sharp angles at cut 
off, or release should be regarded with suspicion until it is 
proved beyond all doubt to be truthful. 

Fig. 201 represents a diagram from a vertical non-con- 
densing engine 14x16 inches^ with riding cut oJBf, which the 
author was called upon to adjust. This engine was nearly 
new, having been run but a few months, and although the 




Fig. 201 

size of it was ample to do all the work required, yet it had 
failed, so far, to supply one-half the power needed. After 
taking the diagram and making a few outside investiga- 
tions, the cause of the trouble was apparent. Indeed, the 
wonder was that the engine had supplied as much power as 
it had under the circumstances. 

First. It was situated too far from the boiler plant, 
being fully 1,200 feet, and although a pressure of 85 
pounds was carried at the boilers and the steam was con- 
veyed through a 6-inch pipe, yet owing to the many drains 
on the pipe for heating buildings, running other small en- 
gines, etc., by the time the steam reached the engine in 
question the pressure was reduced so much that a 30 spring 



Diagram Analysis 515 

was found to be too strong, although that was the scale of 
Fig. 201. 

Second, the end of the exhaust pipe was found to be sub- 
merged in a nearby pond of water to which it had been 
carried, probably with a view of making a condensing en- 
gine out of it ! It was also found that there were no less 
than four superfluous elbows in the exhaust pipe that could 
easily be dispensed with. The diagram shows that the cut 
off was practically .useless. That the back pressure was 
nearly 6 pounds above the atmosphere, and that the engine 
was using 55 pounds of steam and 7 pounds of coal per 




Fig. 202 

horse power per hour, all of which conditions were about as 
bad as they could be. 

After increasing the lead and adjusting the cut off a 
No. 16 spring was used and Pig. 202 was produced which, 
although still showing late admission, is an improvement 
over the original diagram. The initial pressure being only 
30 pounds above the atmosphere, further work with the in- 
dicator was deferred until changes were made in the steam 
and exhaust pipes, by which the initial pressure was in- 
creased to 55 pounds and the exhaust pipe was freed of 
extra turns and raised from its watery grave into the open 
air. The engine has since then given perfect satisfaction. 



516 Steam Engineering 

Fig. 203 is from a Buckeye automatic cut off engine 
18x36 inches. The engine had been running for several 
years with the valves in the condition shown by the di- 
agram^ and in the meanwhile^ the load having been in- 
creased from time to time^ the engine finally refused to 
run up to speed and something had to be done. The 
superintendent of the plant said that he had an idea that 
something was the matter with the engine but could not 
ascertain what it was^ and so he finally called upon the 
author to apply the indicator. The result was that diagram 
Fig. 203 was obtained^ showing that the principle cause of 




Fig. 203 

the trouble was unequal cut off. After equalizing the cut 
off and increasing the lead on the crank end by a small 
fraction diagram Fig. 204 was taken^ and after this the 
engine gave no further trouble. The depression in the 
steam lines might have been rectified to some extent by in- 
creasing the boiler pressure^ thus giving a higher initial 
pressure and an earlier cut off. The speed of the engine 
was 94 E. P. M.^ with a boiler pressure of 70 pounds. A 
40 spring was used Avith the indicator. 

In order to more fully illustrate the process of ascertain- 
ing the M. E. P. mthout dividing the diagram into ordi- 
nates^ the following computation is given together with 



Diagram Analysis 



517 



rules^ etc. In this process two important factors are neces- 
sary^ viz., the absolute initial pressure, and the absolute ter- 
minal pressure, and they can both be obtained from the 
diagram by measuring with the scale adapted to the spring 
used. Thus, in Fig. 204 the absolute initial pressure 
measured from the line of perfect vacuum V to line B is 
77 pounds, and the absolute terminal pressure measured 
from V to line B' is 21 pounds. The ratio, or number of 
expansions, is found thus : 

Rule. Divide the absolute initial pressure by the abso- 
lute terminal pressure; thus, 77-1-21=3. 65=number of 
expansions. 




Fig. 204 

Second. Find mean forward pressure. 

Rule. Multiply absolute initial pressure by the hyper- 
bolic logarithm of number of expansions plus 1, and divide 
product by number of expansions. Thus, referring to Table 
33, it will be seen that the hyperbolic logarithm of 3.65 is 

77X2 2947 

1.2947, to which 1 must be added. Then =48.4 

3.65 

pounds, which is the absolute mean forward pressure. From 

this deduct the absolute back pressure, which is 16 pounds or 

1 pound above atmosphere; thus, 48.4 — 16=32.4 pounds 

M. E. P. 



518 Steam Engineering 

Third. Find I. H. P. 

Area of piston minus one-half area of rod X M. E. P. 

X piston speed in feet per minute^ divided by 33^000. 

250.96X32,4X564 

Thus (the diameter of rod being 3 in.). 

^ ^ 'V 33^000 

= 138.9 I. H. P. 

The steam consumption per I. H. P. per hour may also 
he computed by means of Table 34, which was originally 
calculated by Mr. Thomson, and is based upon the follow- 
ing theory : 

A horse power=33,000 feet pounds per minute, or 
1,980,000 feet pounds per hour, or 1,980,000 Xl^='^3,- 
760,000 inch pounds per hour, meaning that the same 
amount of energy required to lift 33,000 pounds one foot 
high in one minute of time would lift 23,760,000 pounds 
one inch high in one minute of time. Now if an engine 
were driven by a fluid that weighed one pound per cubic 
inch, and the mean effective pressure of this fluid upon the 
piston was one pound per square inch, it would require 23,- 
760,000 pounds of the fluid per horse power per hour. But, 
if in place of the heavier fluid we substitute pure distilled 
water of which it requires 27.648 cubic inches to weigh one 
pound, the consumption per I. H. P. per hour will be con- 
siderably less; as, for instance, 23,760,000^27.648=z859^- 
375 pounds, which would be the rate per hour of the water 
driven engine if the M. E. P. of the water was one pound 
per square inch, and if the M. E. P. was increased to 20 
pounds then twenty times more power would be developed 
with the same volume of water, but the weight of water 
consumed per H. P. per hour would be proportionately 
less. Kow if the engine is driven by steam it will consume 
just as much less water in proportion as the water required 



Diagram Analysis 519 

to make the steam is less in volume than the steam used. 
Therefore if the above constant number^ 859,375, be di- 
vided by the M. E. P. of any diagram, and by the volume 
of the terminal pressure, the quotient will be the water (or 
steam) consumption per I. H. P. per hour. 

Eeferring to Table 34, the numbers in the W columns 
are the quotients obtained by dividing the constant, 859,- 
375, by the volumes of the absolute pressures given in the 
columns under T. P. and which represent terminal pres- 
sures. The table is considerably abridged from the orig- 
inal, which was very full and complete, the pressures ad- 
vancing by tenths of a pound from 3 pounds to 60 pounds ; 
but it is seldom that in ordinary practice there is needed 
such accuracy. If at any time, however, a diagram should 
show a terminal pressure not given in the table, the correct 
factor for that pressure can be easily found by dividing 
the constant 859,375, by the relative volume of the pres- 
sure as found in Table 17 of the properties of saturated 
steam. 

Eeferring again to Fig. 204, it is seen that the terminal 
pressure is 21 pounds absolute, and by reference to Table 
34 and glancing down column T. P. until 21 is reached, it 
will be seen that the number opposite in column W is 
732.69. This number divided by the M. E. P. of the 
diagram Pig. 204, which is 32.4 pounds, gives 22.6 pounds 
per I. H. P. per hour as the steam consumption. The rate 
thus found makes no allowance for clearance and compres- 
sion, however, and these two very important items will be 
treated upon in succeeding pages. 



520 



Steam Engineering 

Table 34 
power factors. 



T. P. 


W. 


T. P. 


W. 


T. P. 


W. 


3 


117.30 


13. 


466.57 


23 


798. lu 


3.5 


135.75 


13.5 


483.43 


23.5 


814.39 


4 


153.88 


14 


500.22 


24 


830.64 


4.5 


171.94 


14.5 


517.07 


24.5 


846.96 


5 


186.75 


15 


533.85 


25 


863.25 


5.5 


207.60 


15.5 


550.64 


25.5 


879.49 


6 


225.24 


16 


567.36 


26 


895.70 


6.5 


242.97 


16.5 


584.10 


26.5 


911.86 


7 


260.54 


17 


600.78 


27 


927.99 


7.5 


278.06 


17.5 


617.40 


27.5 


944.07 


8 


295.44 


18 


633.96 


28 


960.12 


8.5 


312.80 


18.5 


650.46 


28.5 


976.27 


9 


330.03 


19 


666.90 


29 


992.38 


9.5 


347.27 


19.5 


683.38 


29.5 


1008.46 


10 


364.40 


20 


699.80 


30 


1024.50 


10.5 


381.57 


20.5 


716.27 


30.5 


1040.51 


11 


398.64 


21 


732.69 


31 


1056.48 


11.5 


415.73 


21.5 


749.06 


31.5 


1072.42 


12 


432.72 


22 


765.38 


32 


1088.32 


12.5 


449.69 


22.5 


781.76 


32.5 


1104.35 



Fig. 205 is from a Hamilton Corliss non-condensing en- 
gine 32% in. bore by 72 in. stroke. A ISTo. 60 spring was 
used, the boiler pressure being 85 pounds gauge. The 
I. H. P. was 652.2 and the steam consumption per I. H. P. 
per hour was 22.9 pounds. 







Fig. 205 



There are but few points about the diagram that are 
open to criticism. The compression is rather high for so 
large an engine and the steam lines should be maintained 
more nearly horizontal up to the point of cut off. 



II 



Diagram Analysis 521 



Steam Consumption from Indicator Diagrams. In cal- 
culating the steam consumption of an engine, two very im- 
portant factors must not be lost sight of, viz., clearance and 
compression. Especially is this the case in regard to clear- 
ance when there is little or no compression, for the reason 
that the steam required to fill the clearance space at each 
stroke of the engine is practically wasted, and all of it 
passes into the atmosphere or the condensor, as the case 
may be, without having done any useful work, except to 
merely fill the space devoted to clearance. On the other 
hand, if the exhaust valve is closed before the piston com- 




FiG. 206 

pletes the return stroke, the steam then remaining in the 
cylinder will be compressed into the clearance space and can 
be deducted from the total volume which, without compres- 
sion, would have been exhausted at the terminal pressure. 
Figs 206 and 207, which are reproductions of diagrams 
taken by the author while adjusting the valves on a 16x 
42 inch Corliss engine, will serve to graphically illustrate 
this point. Pig. 206, which was the first one to be taken, 
shows no compression. The point of admission at A is 
plainly defined by the square corner at the extreme end of 
the stroke. The clearance of this engine is 4 per cent, of 



522 Steam Engineering 

the volume of the piston displacement. The engine being 
16 inch bore by 42 inch stroke, the piston displacement is 
found by the following calculation : Area of piston, 201.06 
square inches X stroke, 42 inches=8444.52 cubic inches. 
The. volume of clearance space is equal to 8444.52 cubic 
inches X .04=337.78 cubic inches, which divided by 1,728 
r=.195 cubic feet. 

By reference to Fig. 207, taken after adjusting the valves 
for compression, it will be noticed that the steam is there 
compressed to 37 pounds, the compression curve beginning 
at C and ending at B. There is therefore compressed dur- 



FiG. 207 

ing each stroke a volume of steam equal to .195 cubic feet 
at a pressure of 37 pounds gauge, or 52 pounds absolute. 

One cubic foot of steam at 52 pounds absolute pressure 
weighs .1243 pounds, and .195 cubic feet will weigh .1243 
X.195=.0242 pounds. 

The engine was running at 70 E. P. M., or 140 strokes 
per minute. Thus, according to Fig. 207, the total weight 
of steam compressed and doing useful work during one 
hour, and which without compression would have passed 
out through the exhaust pipe, is equal to .0242X14:0X60 
=203.28 pounds. 



Diagram Analysis 523 

B Now in order to estimate the steam consumption of the 
above engine from diagram Pig. 206, it would be necessary 
. to account for all the steam occupying not only the volume 
of the piston displacement at the end of the stroke, but the 
clearance as well, for the reason, as before stated, that it 
would all be released before exhaust closure. This would 
equal 8444.52 cubic inches + 337.78 cubic inches=8782.3 
cubic inches, which divided by 1,728=5.08 cubic feet each 
stroke, or 10.16 cubic feet each revolution. 

The absolute terminal pressure of Pig. 206 is 20 pounds. 
One cubic foot of steam at this pressure weighs .0507 
pounds, and the weight of steam consumed each revolution 
would therefore be 10. 16X. 0507=. 515 pounds, which mul- 
tiplied by 70 E. P. M.=36.05 pounds per minute, or 2,163 
pounds per hour. The horse power developed by the engine 
at the time was 80. Therefore the steam consumption per 
I. H. P. per hour=2,163^80=27 pounds. 

Eef erring again to Pig. 207 it will be remembered that 
the total weight of steam compressed during one hour was 
203.28 pounds. The weight of steam consumed per hour, 
therefore, equals 2,163—203.28=1959.7 pounds. 

Owing to compression, the work area of Pig. 207 is some- 
what smaller than that of Pig. 206, amounting in fact to 
the area of the irregular figure enclosed between the points 
A, B and C. The work represented by this figure amounts 
to a very small proportion of the total work indicated by 
Pig. 206, still in order to arrive at correct conclusions, it 
should be deducted therefrom. 

Assuming the negative work to be equal to .55 horse 
power, we have 80 — .55=79.45 I. H. P. as the work repre- 
sented by Pig. 80. As the total weight of steam consumed 
in one hour was 1959.7 pounds, the steam consumption per 



p24 Steam Engineering 

I. H. P. per hour ^vill be 1959.7-f-79.45=24.67 pounds, a 
saving by compression of 2.33 pounds per H. P. per hour, 
besides the great advantage of having a cushion of steam 
in contact with the piston at the termination of the stroke, 
thus bringing the moving parts of the engine to rest quietly 
without shock or jar. 

The steam consumption may also be computed from the 
diagram, regardless of the dimensions of the cylinder or 
the horse power developed. The mean effective pressure 
and also the absolute terminal pressure must, however, be 



Fig. 208 

known. This method has already been referred to, but in 
the computation therein made, no correction was made for 
clearance and compression. 

Having reviewed these two factors at considerable length 
it will now be in order to more fully explain the methods 
of treating diagrams when it is desired to make these cor- 
rections. 

First, draw vertical lines C and D, Fig. 208, at each end 
of the diagram, and perpendicular to the atmospheric line. 
Draw line Y, representing perfect vacuum,. 14.7 pounds 
below the atmospheric line, as indicated on the scale adapted 



Diagram Analysis 525 

to the diagram/ which in this case is 50 pounds to the inch. 
Continue the expansion from R^ where release begins, until 
it intersects line D V, from which point the absolute ter- 
minal pressure can be measured. 

Having ascertained the terminal pressure, which for Pig. 
208 is 30 pounds, draw line D E, which may be called the 
consumption line for 30 pounds. The terminal being 30 
pounds, refer to Table 34 and find in column W, opposite 
30 in column T. P., the number 1,024.5. Divide this num- 
ber by the M. E. P. which in Pig. 208 is 41 pounds, and 
the quotient, which is 24.99 pounds, is the uncorrected rate 



Fig. 209 

of steam consumption. This rate stands for the total con- 
sumption throughout the whole stroke represented on the 
diagram by the distance from D to C, which measures 3.25 
inches, but it is evident that there is a small portion of the 
return stroke, that indicated by the distance from E to C, 
during which the steam compressed in the clearance space 
should not be charged to the consumption rate, but sliould 
be deducted therefrom. In order to do this, multiply the 
uncorrected rate by the distance from D to E, which is 
3% inches, or 3.125 inches, and divide the product by the 
distance from D to C, 3^4 inches, or 3.25 inches. Thus, 



526 Steam Engineering 

24.99 X3.125-^3.25=:24.03 pounds, which is the corrected 
rate and represents a saving by compression of 24.99 — 24.03 
r=.96 pounds, or nearly 3.7 per cent. 

In many cases the terminal pressure greatly exceeds the 
compression, an illustration of which is given in Fig. 209 
which is a reproduction of a diagram from an old Wheelock 
engine. It now becomes necessary to extend the compres- 
sion curve to L, a point equidistant from the vacuum line 
with the terminal at E. The consumption line E. L. now 




Fig. 210 

becomes longer than the stroke line E. M., therefore the 
corrected rate will exceed the uncorrected rate by just so 
much; as for instance, terminal pressures 34 pounds. The 
factor, as per Table 34,=:1152.26, and the M. E. P. of the 
diagram is 47 pounds. Then, 1,152.26-^-47=24.5 pounds, 
uncorrected rate; 24.5X3.125 inches (distance E. L.)-^3 
inches (distance E. M.) =25.52 pounds, corrected rate, a 
loss of a little more than one pound, or about 4 per cent. 

There is another class of diagrams very frequently en- 
countered in which the terminal pressure is considerably 



Diagram Analysis 527 

below the compression curve, and in order to compute the 
consumption rate by the above method it becomes necessary 
to continue the compression curve downwards until it meets 
the terminal, as illustrated at A, Fig. 210, which is a fric- 
tion diagram from a Buckeye engine. E is the point of 
release, D A represents the consumption line, and D C the 
stroke. The terminal is 8.5 pounds, and the factor for that 
pressure, according to Table 34, is 312.8. Dividing this 
number by the M. E. P., which was 7 pounds, gives 44.6 
pounds as the uncorrected rate. The distance D to A, where 
the compression curve intersects the consumption line, is 
2.625 inches, and the total length of the diagram C to D 
is 3.375 inches. Then 44.6X2.625-^3.375=35 pounds as 
the corrected rate. The extremely high rate is owing to 
the fact that the engine was running light, no load except 
a line of empty shafting. 

Theoretical Clearance. The expansion and compression 
curves of a diagram are created by the expansion and com- 
pression of all the steam admitted during the stroke. This 
Includes the steam in the clearance space as well as in the 
cylinder proper. It is evident, therefore, that the volume 
of the clearance is one of the factors controlling the form 
of these curves, and when the clearance is known a correct 
expansion or isothermal curve may be theoretically con- 
structed, as will be explained later on. Also if the actual 
curves, either expansion or compression, of a diagram as- 
sume an approximately correct form, the clearance, if not 
already known, may be determined theoretically from them ; 
although too much confidence should not be put in the re- 
sults as they are liable to show either too little, or too much 
clearance, generally the latter, especially if figured from 
the compression curve. 



528 



Steam Engineering 



For the benefit of those who may desire to test this method 
of ascertaining the percentage of clearance of their en- 
gines^ several illustrations will be given of its application 
to actual diagrams taken from engines in which the clear- 
ance was known. 

Fig. 211 is from an engine in which the clearance was 
known to be 5 per cent. As compression cuts but a very 
small figure in this diagram^ the expansion curve alone will 
be utilized for obtaining the theoretical clearance^ and the 
process is as follows: 




Fig. 211 



Select two points^ C and E^ in the curve as far apart as 
possible^ but be sure that they are each within the limits of 
the true curve. Thus C is located just after cut off takes 
place^ and R is at a point just before release begins. From 
C draw line C D parallel with the atmospheric line. From 
D draw line D R^ and from C draw line C E^ both perpen- 
dicular to the atmospheric line. Then from E draw line 
E E^ forming a rectangular parallelogram^ C D E E^, with 
two opposite corners^, C and E^ within the curve. Now 



Diagram Analysis 



529 



through the other two corners^ D and E^ draw the diagonal 
D E, extending it downwards until it intersects the vacuum 
line V. From this point erect the vertical line V W^ which 
is the theoretical clearance line. 

To prove the result proceed as follows: Measure the 
length of diagram from P to G^ which in this case is 3.75 
inches^ representing piston displacement. Next measure 
the distance from F to the clearance line V W^ which is 
3.91 inches^ representing piston displacement with volume 
of clearance added. Then 3.91 — 3. 75=. 16^ which repre- 
sents volume of clearance; and .16X100-f-3. 75=4.3 per 
cent^ which is approximately near the actual clearance, 
which, as before stated, was 5 per cent. 



cL . \ V 



Fig. 212 



Fig. 212 serves to illustrate the same method applied to 
the compression curve. This diagram is a reproduction of 
one taken from the low pressure cylinder of a large com- 
pound condensing Corliss engine in which the actual clear- 
ance was 2.25 per cent. Two points, G and H, are selected 
in the compression curve, and from them the parallelogram 
G H I K is erected with two of its opposite corners, G and 
H, well within the limits of the curve, while through the 
other two corners, I and K, the diagonal I K C is drawn 
intersecting the vacuum line at C, thus locating the point 



530 Steam Engineering 

from which the clearance line C D can be drawn. The 
measurements in this case are as follows : 

Total length of diagram, E to P=3.75 inches. 

Distance from clearance line, D C, to Fi=3.875 inches. 

Volume of clearance =3.87 5 — 3. 75=:. 125 inches. 

.125X100^3.75=3.33 per cent clearance, which is 1.08 
per cent more than the known clearance. 

However, notwithstanding the liability to error in many 
cases, still this method of computing clearance may often 
be utilized to good advantage. 

Another and more practical method of measuring clear- 
ance is as follows : Place the engine on the dead center. 
Eemove the valve chest cover and take out the valve. Close 
the cylinder cock on that end of the cylinder to which the 
piston has been moved, leaving the cock on the opposite end 
of the cylinder open and disconnected from its drip pipe, 
so as to give an opportunity for catching any water that may 
leak past the piston while measuring the clearance space. 
Then having first provided a known weight of water, al- 
ways making sure of having a little more than enough, pour 
it into the steam port until the clearance space is filled to 
a level with the valve seat. When this is done, weigh the 
water that is left and deduct it from the original quantity, 
and the remainder will be the number of pounds of water 
required to fill the clearance, from which it is an easy mat- 
ter to compute the number of cubic inches or cubic feet in 
the space devoted to clearance. If any water leaks past the 
piston during the operation it should be weighed and de- 
ducted from the total quantity poured into the port. 

In the case of an engine having the valve chest on the 
side of the cylinder it will be necessary to close the steam 
port either by blocking the valve against it or by fitting a 



• Diagram Analysis 531 

piece of soft wood into it^ making it water tight. The 
water can then be poured into the clearance space through 
a pipe connected to the indicator opening in that end of the 
cylinder. Care should be exercised to allow a vent for 
the air to escape as it is displaced by the water. 

The Theoretical Expansion Curve, According to Boyle^s 
law the volume of all elastic gases is inversely as their 
pressures^ and steam being a gas conforms substantially to 
this law; although the expansion curves of indicator dia- 
grams are affected more or less by the loss of heat trans- 
mitted through the cylinder walls^ and by the change in 
the temperature of the steam produced by the changes in 
pressure during the progress of the stroke. The pressure 
generally falls more rapidly during the first part of the 
stroke^ and less rapidly during the last portion than it 
should in order to conform strictly to the above law^ and the 
terminal pressure usually is greater than it should be to 
agree with the ratio of expansion. But this fullness of the 
expansion curve of the diagram near the end compensates 
in a measure for the too rapid fall near the beginning of 
the stroke. Therefore^ if the engine is in fairly good condi- 
tion with the valves properly adjusted^ and not leaking^, and 
the piston rings are steam tight^ it may be assumed that the 
expansion of the steam in the cylinder takes place according 
to Boyle's law and it is found that the expansion curve 
drawn by the indicator practically coincides with a hyper- 
bolic curve constructed according to that law. 

Fig. 213 graphically illustrates the application of the 
hyperbolic law to the expansion of gases. The horizontal 
lines represent volumes and the vertical lines represent 
pressures. The base line, A P, represents the full stroke of 
a piston in the cylinder of an engine/ and the vertical line 



532 



Steam Engineering 



A I represents the pressure of the steam at the commence- 
ment of the stroke. 

Suppose there is no clearance and that the steam has 
been admitted up to point H when it is cut aff. The rect- 
angle A B H I is the product of the pressure multiplied 
by the volume of the steam thus admitted. When the 
piston has traveled from A to C the volume of the steam has 
been doubled and the pressure C L has been reduced to just 
one-half what it was at A I^ but the area of the rectangle 



JS 


H 


w 

1 


1 ==4^ 







Af 



Fig. 218 



JO CJff A 



A C L M is equal to the area of the initial rectangle, and^ 
as before^ is the product of the pressure C L multiplied by 
the volume AC. As the piston travels still farther^ as 
from A to D^ the steam is expanded to four volumes while 
the pressure at D K will only be one-fourth that of the 
initial pressure; but the new rectangle A D K N is still 
equal in area to either of the others^ A B H I or A C L M. 
The same laAV applies to each of the' remaining rectangles ; 
A E G representing five volumes and one-fifth of the 
initial pressure, and A F E P representing six times the 



Diagram Analysis 



533 



initial volume and one-sixth of the initial pressure, but 
each having the same area as the initial rectangle A B H I. 
Now the area of the rectangle A B H I represents the work 
done by the steam up to the point of cut off, and the area 
of the hyperbolic figure enclosed by the lines B H E F 
represents the work done by the expansion of the steam after 
cut off occurs. 

This area and the amount of work it represents may be 
computed by means of the known relations of hyperbohc 
surfaces with their base lines; as for instance, if the base 




Fig. 214 



lines A B, A C, A D^ etc., extend in geometrical ratio, as 
1, 2, 4, 8, 16, etc., the successive areas, B H L C, B H K D, 
B H Gr E, etc., increase in arithmetical ratio, as 1, 2, 3, 4, 
etc. 

On the principles of common logarithms, which represent 
in arithmetical ratio natural numbers in geometrical ratio, 
tables of hyperbolic logarithms (see table 33) have been com- 
puted for the purpose of facilitating the calculation of 
areas of work due to different degrees of expansion. 

A theoretical curve may be constructed conjointly with 
the actual expansion curve of a diagram by first locating 



534 Steam Engineering 

the clearance and vacuum lines^ and then pursuing the 
method illustrated by Pig. 214. A curve so produced is 
called an isothermal curve^ meaning a curve of the same 
temperature. 

Eef erring to Fig. 214, suppose, first, that it is desired to 
ascertain how near the expansion curve of the diagram 
coincides with the isothermal curve, at or near the point 
of cut oflE. Select point E near where release begins, but 
still well within the expansion curve. Prom this point draw 
the vertical line, E T, parallel with the clearance line, V S. 
Then draw the horizontal line, S T, parallel with the at- 
mospheric line, and at such a height above it as will equal 
the boiler pressure as measured by the scale adapted to the 
diagrani; such measurement to be made from the atmos- 
pheric line to correspond with the gauge pressure. Prom 
T draw the diagonal T V, and from E draw the horizontal 
line E D parallel with the atmospheric line. Prom D, 
where this line intersects T V, erect the perpendicular D E, 
thus forming the parallelogram E D E T, and as line T V 
passes through two of its opposite angles and meets the 
junction of the clearance and vacuum lines, the other two 
angles, E and E, will be in the theoretical curve, and E be- 
ing the starting point, it is obvious that this curve must 
pass through E, which would be the theoretical point of 
«ut off on the steam line S T. 

Two important points in the theoretical curve have now 
been located, viz., E as the cut off, and E as the point of 
release. In order to obtain intermediate points, draw any 
desired number of lines downward from points in S T, as 
1, 2, 3, 4, 5, etc., and continue them downwards far enough 
to be sure that they will meet the intended curve, and from 
the same points in S T draw diagonals 1 V, 2 V, 3 V, 4 V, 



Diagram Analysis 



535 



5 V, etc., all to converge accurately at V. From the inter- 
section of these diagonals with D E draw horizontal lines 
parallel with V V, and the points of junction of these lines 
with the vertical lines will be points in the theoretical curve. 
It will now be an easy matter to trace the curve through 
these points. If, on the other hand, it be desired to com- 
pare the curves toward the exhaust end of the diagram, 
draw lines E D and E T, Fig. 215, also T E, locating E 
near where release commences, after which draw line E D, 
completing the parallelogram E T E D, fixing E as a point 
in the theoretical curve started at E. After drawing the 




Fig. 215 



diagonal T V, proceed in the same manner as before to 
locate the intermediate points. 

It will be observed that in order to ascertain the perform- 
ance of the steam near the beginning of the stroke, the 
starting point of the isothermal curve must be near the 
point of release, and conversely, if the starting point of the 
curve is located near the point of cut off and coincident 
with the actual curve, the test will apply towards the end 
of the stroke. It is not to be expected that the expansion 
curve of any diagram taken in practice will conform strictly 
to the lines of the isothermal curve, especially towards the 



536 



Steam Engineering 



latter end of the stroke^ owing to the reevaporation of water 
resulting from the condensation of steam which was re- 
tained in the cylinder by the closing of the exhaust valve. 
This reevaporation commences just as soon as the tempera- 
ture of the steam^ owing to reduction of pressure due to 
expansion^ falls below the temperature of the cylinder walls, 
and it continues at an increasing rate until release occurs. 
The tendency of this reevaporation^ or generation of steam 
within the cylinder during the latter portion of the stroke 
is to raise the terminal pressure considerably above what 



T 


Ic 




5 

80 




/ ^ — 


■js 




' X 


7« 




// 


Tf 




J / 


4« 




/ / 


iJ 




^x 


5o 




.-:/ 


H5 




^ -ix^ 






.^^ 


.3S 




-^s>^ 


. 3o 


R 




2^ 


c 


^ . 


_^ 


A 


V 


. 




Y , 



Fig. 216 



it would be if true isothermal expansion, took place. The 
terminal pressure may also be augmented by a leaky steam 
valve^ while^ on the other hand a leaky piston would cause 
a lowering of the terminal and an increase in the back 
pressure. 

T}ie Adiabatic Curve. If it were possible to so protect, 
or insulate the cylinder of a steam engine that there would 
be absolutely no transmission of heat either to or from 
the steam during expansion, a true adiabatic curve or ^^curve 
of no transmission^^ might be obtained. The closer the 
actual expansion curve of a diagram conforms to such a 



Diagram Analysis • 537 

curve^, the higher will be the efficiency of ihe engine as a 
machine for converting heat into work. 

Fig. 216 illustrates a method of figuring a curve which^ 
while not strictly adiabatic^ will be near enough for all 
practical purposes^ while at the same time it will give the 
student an opportunity to study the laws governing the 
expansion of saturated steam. 

To draw the curve^ first locate the clearance and vacuum 
lines V S and V V. Kext locate point E in the expansion 
curve near where release begins^, making this the starting 
pointy and also the point of coincidence of the expansion 
curve with the adiabatic curve. The other points in the 
curve are located from the volumes of steam at different 
pressures during expansion; the pressures being measured 
from the line of perfect vacuum^ and the volumes from the 
clearance line. 

The absolute pressure at E, Pig. 216^ is 26 pounds. From 
point E erect the perpendicular E T. Also draw horizontal 
line E 26 parallel with the vacuum line and at a height 
equal to 26 pounds above vacuum line V V'^ as shown by 
the scale, which in this case was 40. The length of line 
E 26, measured from E to the clearance line, is SyV inches, 
or 3.0625 inches. By reference to Table 17 it will be seen 
that the volume of steam at 26 pounds absolute, as com- 
pared with water at 39 '^, is 962. Now if the length of line 
E 26 be divided by this volume, and the quotient multi- 
plied by each of the volumes of the other pressures repre- 
sented at points 30, 35, 40, 45, etc., up to the initial pres- 
sure, the products will be the respective distances from the 
clearance line of points in the adiabatic curve. These 
points can be marked on the horizontal lines drawn from 
the clearance line to line E T. 



538 



Steam Engineenng 



Starting with line E 26^ it has been noted that its length 
is 3.0625 inches^ and that the volume was 962. 3.0625-^ 
962^.003. Then the volume of steam at 30 pounds is 
841, which being multiplied by .003=2.5 inches, the length 
of line 30. Next the volume at 35 pounds=728. Multiply- 
ing this volume by .003=2.1 inches, length of line 35, and 
so in like manner for each of the other points. 

The process involves considerable figuring and careful 
and accurate measurements, which should be made with a 




steel rule with decimal graduations. It is not expected that 
the cut Fig. 216 will be found accurate enough in its meas- 
urements to serve as a standard; it being intended only to 
serve as an illustration of the process. The diagram from 
which the illustration was drawn was taken from a 600 
H. P. engine situated some 200 feet from the boilers, and 
there was a considerable cooling of the steam by the time it 
Teached the engine, the effect of which is apparent. The 
curve produced by the measurements is shown by the broken 
line. The process can be applied to any diagram. 



Diagram, Analysis 539 

Power Calculations, The area of the piston (minns one- 
half the area of rod) multiplied by the M. E. P.^ as shown 
by the diagram, and this product multiplied by the number 
of feet traveled by the piston per minute (piston speed) 
will give the number of foot pounds of work done by the 
engine each minute, and if this product be divided by 33,000, 
the quotient will be the indicated horse power (I. H. P.) 
developed by the engine. 

Therefore one of the first requisites in power calculations 
is to ascertain the M. E. P. Beginning with the most 
simple, though only approximately correct, method of ob- 
taining the average pressure, as illustrated by Fig. 217, 
draw line A B touching at A and cutting the diagram in 
such manner that the space D above it will equal in area 
spaces C and E taken together, as nearly as can be estimated 
by the eye. Then with the scale measure the pressure along 
the line F G- at the middle of the diagram, which will be 
the M. E. P. 

The process is based upon the theory that the average 
width of any tapering figure is its width at the middle of 
its length. This method should not be relied upon as accu- 
rate, but is convenient at times when it is desired to make 
a rough estimate of the horse power of an engine. 

Ordinates, The method of calculating the M. E. P. by 
the use of ordinates has already been alluded to, and will 
be here enlarged upon. The process consists in drawing 
any convenient number of vertical lines perpendicular to 
the atmospheric line across the face of the diagram, spac- 
ing them equally, with the exception of the two end spaces, 
which should be one-half the width of the others, for the 
reason that the ordinates stand for the centers of equal 
spaces, as for instance, line 1, Fig. 218, stands for that 



540 



Steam Engineering 



portion of the diagram from the end to the middle of the 
space between it and line 2. Again^ line 2 stands for the 
remaining half of the second space and the first half of 
the thirds and so on. This is an important matter, and 
should be thoroughly understood, because if the spaces are 
all made of equal width, and measurements are taken on 
the ordinates, the result will be incorrect, especially in the 
case of high initial pressure and early cut off, following 
which the steam undergoes great changes. 



Cf^nK^-nti 




iiri-i-io 'Zi.j/^i^n.FT^ 



S^K B-£s5y tF^ 3 



^iicKj}t 



■ffT7r.n£.p, 



J 



Fig. 218 



If the spaces are all made equal^ the measurements will 
require to be taken in the middle of them, and errors are 
liable to occur, whereas if spaced as before described, the 
measurements can be made on the ordinates, which is much 
more convenient and will insure correct results. Any num- 
ber of ordinates can be drawn, but .ten is the most conven- 
ient and is amply sufficient, except in case the diagram is 
excessively long. For spacing the ordinates, dividers may 
be used, or a parallel ruler may be procured from the 
makers of the indicator; but one of the most convenient 
and easily procurable instruments for this purpose is a 



Diagram Analysis 541 

common two-foot Tv\e, and the method of using it is illus- 
trated in Fig. 218. 

First draw vertical lines at each end of the diagram, 
perpendicular to the atmospheric line, and extending down- 
wards to the vacuum line, or below it if necessary, in order 
to have a point on which to lay the rule. In Fig. 218 
points A and B are found to be the most convenient. Now 
lay the rule diagonally across the diagram, touching at A 
and B, and the distance will be found to be 3% inches, or 
60 sixteenths. 

Suppose it be desired to draw 10 ordinates. Divide 60 
by 10, which will give 6 sixteenths, or % inches as the 
width of the spaces, but as the two end spaces are to be 
ane-half the width of the others, there will be 11 spaces 
altogether, the two outer ones having a width equal to one- 
half of % or y^g. Now apply the rule again in the same 
manner, touching at points A and B, and with a sharp 
pointed pencil begin at A and mark the location of the first 
ordinate according to the rule, at a distance of -^q from the 
3nd. Then % from this mark make another one, which will 
bcate the second ordinate, and proceed in like manner to 
locate the others. The last two or three marks generally 
3ome below the diagram, and if the diagram be taken from 
I condensing engine it may be necessary to tack it on to a 
.arger sheet of paper in order to get these points. Having 
correctly located the ordinates, they may now be drawn 
Derpendicular to the atmospheric line or vacuum line, either 
)f which will answer. 

It sho-u^ld be noted that^ owing to the diagonal position 
)f the rule with relation to the atmospheric line, the spaces: 
ire not of the actual width as described by the rule, but this 
s unimportant, so long as they are of a uniform width.. 



542 Steam Engineering 

This method can be applied to any diagram^ no matter 
what its length may be^ and point B may be located at any 
distance below the atmospheric or vacnnm lines, wherever 
it is the most convenient for the subdivisions on the rule, 
sixteenths, eighths, etc., so long as it is in line with the end 
of the diagram. Having thus drawn the ordinates, the 
M. E. P. may be found by measuring the pressure expressed 
by each one, using for this purpose the scale adapted to the 
spring used, adding all together and dividing by the num- 
ber of ordinates which will give the average pressure. 

Referring to Fig. 218, begin with ordinate No. 1 on the 
diagram, from the head end of the cylinder. In this case 
a 40 spring was used. Lay the scale on the ordinate with 
the zero mark where it intersects the compression curve. 
The pressure is seen to be 49 pounds. Set this down at that 
end of the card and measure the pressure along ordinate 
No. 2, which is 55 pounds. Proceed in this manner to 
measure all the ordinates, placing the resulting figures in 
a column, after which add them together and divide by 10. 
The result is 26.71 pounds, which is the mean forward pres- 
sure (M. P. P.). To obtain the mean effective pressure, 
deduct the back pressure, which is represented by the dis- 
tance of the exhaust line of the diagram above the atmos- 
pheric line in a non-condensing engine, and in a condensing 
engine the back pressure is measured from the line of per- 
fect vacuum, 14.7 pounds, according to the scale below the 
atmospheric line. 

In Fig. 218 the back pressure is found to be 3 pounds. 
Therefore the M. E. P. of the head end will be 26.71—3= fk 
23.71 pounds. On the crank end the M. F. P. is 27.23 
pounds, and 27.23—3=24.23 pounds=M. E. P. The 
average effective pressure on the piston, therefore, will be 
23.71-f24.23^2=23.97 pounds. 



k 



Diagram Analysis 



543 



Unless great care is. exercised in the measurements, errors 
are liable to occur in applying this method, especially with 
scales representing high pressures, as 60, 80, etc. The most 
sonvenient and reliable method is to take a narrow strip 
of paper of sufficient length, and starting at one end, apply 
its edge to each ordinate in succession, and mark their 
lengths on it consecutively, with the point of a knife blade 
or a sharp pencil. Having thus marked on the paper the 
total length of all the ordinates, ascertain the number of 
inches and fractions of an inch thereon, the fractions to be 







Fig. 219 



expressed decimally, and divide by the number of ordinates. 
The quotient will be the average height of the diagram, and 
as the scale expresses the number of pounds pressure for 
each inch, or fraction of an inch in height, if the average 
height of the diagram be multiplied by the number of the 
[ scale, the product will be the M. F. P. 

Eef erring again to Pig. 218, if the lengths of the ordinates 
[drawn on the head end diagram be measured, their sum will 
ibe found to be 6 8/12 or QMQ inches. Dividing this by 



•M4 Steam Engineering 

10 gives .^^^ inches as the average height. The mean for- 
ward pressure will then be as follows: .666X40=26.64 
pounds^ or practically the same as found by the other 
method. 

Fig. 219 illustrates a type of diagram frequently met 
wdth^ and one which requires somewhat different treatment 
in estimating the power developed. It will be noticed that, 
owing to light load and early cut oil, the expansion curve 
drops considerably below the atmospheric line, notwith- 
standing that the engine from which this diagram was 
taken is a non-condensing engine. When release occurs at 
E, and the exhaust side of the piston is exposed to the atmos- 
phere, the pressure immediately rises to a point equal to, 
or slightly above, that of the atmosphere. 

Fig. 219 was taken during a series of experiments made 
by the author for the purpose of ascertaining the friction 
of shafting and machinery, and the engine it was obtained 
from is a Buckeye 24x48 inches. The boiler pressure at 
the time was only 40 pounds, and a No. 20 spring was used. 
The ordinates are drawn according to the method illustrated 
in Fig. 218. By placing the rule on points A and B, the 
distance between those two points is found to be 3% inches, 
or 58 sixteenths. Dividing this by 10 gives 5.8 sixteenths, 
or nearly % inches, as the width of the spaces ; the two end 
spaces being one-half of this, or -^q inches wide. The first 
five ordinates, counting from A, express forward pressure, 
represented by the arrows. The remaining five ordinates, 
counting from B, express counter or back pressure, repre- 
sented by the arrows pointing in the opposite direction. 
Measuring the pressures along the first five ordinates, and 
adding them together, gives 63.1 pounds, which divided by 
5 gives 12.65 pounds as the mean forward pressure (M. 
P.P.). 



Diagram Analysis 545 

Then figuring np the counter pressure in the same man- 
ner on the other five ordinates^ beginning at B, the result 
is 4.25 pounds. The M. E. P. therefore will be 12.65—4.25 
=8.4 pounds. 

Obtaining the M. E. P. with the Planimeter, The area 
of the diagram represents the actual work done by the 
steam acting upon the piston. In a non-condensing engine 
the lower^ or exhaust line of the diagram must be either 
coincident with or slightly above the atmospheric line in 
ord^r to express positive work. Any deviation of this line, 
either above or below the atmospheric line, represents 
counter pressure, the amount of which may be ascertained 
by measurements with the scale, and should be deducted 
from the mean forward pressure. 

On the other hand, the exhaust line of a diagram from 
a condensing engine falls more or less below the atmos- 
pheric line, according to the degree of vacuum maintained, 
and the nearer this line approaches the line of perfect 
vacuum, as drawn by the scale, 14.7 pounds below the at- 
mospheric line, the less will be the counter pressure, which 
in this case is expressed by the distance the exhaust line is 
above that of perfect vacuum. 

The prime requisite therefore in making power calcu- 
lations from indicator diagrams is to obtain the average 
height or width of the diagram, supposing it were reduced 
to a plain parallelogram instead of the irregular figure which 
it is. 

The planimeter. Figs. 220-221, is an instrument which 
will accurately measure the area of any plane surface, no 
matter how irregular the outline or boundary line is, and 
it is particularly adapted for measuring the areas of indi- 
cator diagrams, and in cases where there are many diagrams 



546 



Steam Engineering 



to work up^ it is a very convenient instrument and saves 
much time and mental effort. In fact^ the planimeter has 




Fig. 220 

COFFIN AVERAGER OR PLANIMETER 



of late years become an almost indispensable adjunct of the 
indicator. It shows at once the area of the diagram in 
square inches and decimal fractions of a square inch, and 



Diagram Analysis 



547 



when the area is thus known it is an easy matter to obtain 
the average height by simply dividing the area in inches by 
the length of the diagram in inches. Having ascertained 
the average height of the diagram in inches or fractions 
of an inch the mean or average pressure is found by multi- 




FiG. 221 



plying the height by the scale. Or the process may be made 
still more simple by first multiplying the area^ as shown 
by the planimeter in square inches and decimals of an inch, 
by the scale^ and dividing the product by the length of tlie 
diagram in inches. The result will be the same as before, 
and troublesome fractions will be avoided. 



548 Steam Engineering 

QUESTIONS AND ANSWERS. 

401. ^What two important points are gained by the use 
of the indicator? 

Ans. First — It shows the average pressure upon the 
piston throughout the stroke. Second — It shows the action 
of the valve or valves in admission^ cut oS and release of 
the steam. 

402. What is the first principle of the indicator? 

Ans. Pressure of the steam in the engine cylinder dur- 
ing an entire revolution^ against a small piston in the cylin- 
der of the indicator. 

403. What resistance is in front of the indicator piston? 
Ans. A spiral spring of kndwn tension. • 

404. What is the second principle of the indicator ? 
Ans. By means of a multiplying mechanism of levers, 

the stroke of the indicator piston is communicated to a 
pencil moving in a straight line. 

405. What is the third principle of the indicator? 
Ans. By means of a reducing mechanism and cord, the 

motion of the engine piston during* an entire revolution is 
imparted to a small rotating drum, to which is attached a 
piece of blank paper. 

406. How is a diagram obtained? 

Ans. The pencil is held against the paper and thus traces 
a diagram of the action of the steam within the engine 
cylinder. 

407. What is the atmospheric line? 

Ans. A line drawn by the indicator pencil before com- 
munication is established between engine cylinder and indi- 
cator cylinder. 

408. Where should a diagram from a non-condensing 
engine appear relative to the atmospheric line? 



Questions and Answers 549 

Ans, It should appear above the atmospheric h*De. 

409. Where should the diagram from a condensing en- 
gine appear? 

A71S. Partly above^ and partly below the atmospheric 
line. 

410. What is the best reducing motion to use? 
Ans. The reducing wheel. 

411. How is the indicator attached to the engine cylin- 
der? 

Ans. By means of half-inch pipe tapped into the side of 
the cylinder near the ends. 

412. How are the springs numbered? 

Ans, They are made for various pressures^ and num- 
bered accordingly. 

413. What is a good rule to follow in selecting a spring? 
Ans. Select one numbered one-half as high as the boiler 

pressure, which will give a diagram about two inches high. 

414. What data should be noted upon the diagrams 
when they are taken? 

Ans. Boiler pressure; time when taken, and which end 
of cylinder, head, or crank. 

415. What pressure must always be deducted from the 
mean forward pressure (M. P. P.) in calculations for 
power ? 

Ans. The back pressure. 

416. What bad effects follow unequal cut off? 

Ans. The engine will not develop the power that it is 

capable of — uneven strains will be set up. 

417. What is a convenient size for a diagram? 
Ans. 11/^ or 2 inches high, and 2 or 2^/2 inches long. 

418. What precaution regarding the pipe connections 
of the indicator should always be observed before taking 
diagrams ? 



550 Steam Engineering 

Ans. They should be thoroughly blown out, and cleaned 
of all dirt. 

419. How is the ratio of expansions found? 

Ans. Divide absolute initial pressure by absolute ter- 
minal pressure. 

420. N'ame a very important factor in the calculation 
of steam consumption of an engine. . 

Ans. The clearance space. 

421. What is one of the first requisites in power calcu- 
lations? 

Ans. To ascertain the M. E. P. 

422. How is this done? 

Ans. In several ways, for instance by means of ordinates, 
or it nrny be obtained by the use of the Planimeter. 



Friction and Lubrication 

Next to the all important problems of keeping the water 
in the boilers at the proper level, and maintaining a suffi- 
cient supply of steam, comes the proper lubrication of the 
bearings, and other rubbing surfaces on the engine. If 
these are not oiled as they should be, the efficiency of the 
engine will be reduced, and besides there is a constant 
danger of some one of the heavy bearings becoming heated, 
and most likely cause a shut-down. 

In discussing the problem of lubrication it is well to first 
study the laws of friction of plane surfaces in contact. 

There are five of these laws which are commonly accepted 
relative to this subject. 

Friction is the resistance caused by the motion of a body 
when in contact with another body that does not partake 
of its motion, and the laws that control this resistance are 
as follows : 

First — Friction will vary in proportion to the pressure 
on the surfaces, that is if the pressure increases, the fric- 
tion will be increased, and vice versa. 

Second — Friction is independent of the areas of the sur- 
faces in contact, but if the pressure, or friction be distributed 
over a larger area, the liability of heating and abrasion be- 
comes less than it would be if the friction is concentrated 
on a smaller area. 

Third — Friction increases with the roughness of the sur- 
faces, and decreases as the surfaces become smoother. 

Fourth — Friction is greatest at the beginning of motion. 
Greater force is required to overcome the friction at the 

551 



552 Steam Engineering 

instant of starting to move a body^ than is required after 
motion has commenced. 

Fifth — Friction is greater between soft bodies than it 
is between hard bodies. 

These five laws were formulated in the years 1831-33 by 
Gen. Arthur Morin^ a French engineer^ who made many 
experiments relating to the friction of plane surfaces in 
contact^ but numerous experiments in later years by many 
eminent engineers have demonstrated that these laws are 
not altogether rigid^ and that they can only be accepted in 
so far as they relate to the friction of dry surfaces in con- 
tact^ or lubricated surfaces moving under light pressures, 
and at slow speed. As friction is always a resisting, and 
retarding factor, its tendency is to bring everything in mo^ 
tion to a state of rest. With machinery in motion the frici 
tion between the surfaces of the parts moving in contact 
tends to cause them to adhere to each other. 

Therefore in order to successfully and economically oper- 
ate the machinery, it is absolutely necessary that a lubri- 
cant be used that will distribute itself over these surfaces, 
and thus prevent them from coming in direct contact with 
each other. 

Friction, however, is useful in many ways, as for in- 
stance, the friction of the belt in contact with the rim of 
the pulley causes power to be transmitted from the engine 
to the machines throughout the shop. Then, also the fric- 
tion or adhesion of the driving wheels of the locomotive 
makes it possible for the engine to start a heavy train and 
keep it moving. 

The friction of the brake shoes on the car wheels makes it 
possible to stop a train in much less time than if it were 
allowed to stop of its own accord. 



Friction 



553 



There are two kinds of friction in mechanics^ viz., the 
friction of solids, and the friction of liquids. It is the 
friction of solids that the engineer has to deal with mainly, 
and this kind of friction for convenience may be again 
divided into two classes, viz., rolling friction, as for in- 
stance a journal revolving in its bearings, or a crank pin 
in its brasses, and second, sliding friction, as the cross-head 
on the guides, or the piston traveling back and forth in the 
cylinder. 




Fig. 222 



Co-Efficient of Friction. By this term is meant the re- 
lation that the power required to move a body, bears to the 
weight or pressure on that body. 

This definition may be expressed in another, and per- 
haps plainer form, as follows : 

The co-efficient of friction is the ratio between the resist- 
ance to motion, and the perpendicular pressure, and is de- 
termined by dividing the amount of the former by the 
latter. Figures 222 and 223 will serve to illustrate in a 
graphic manner the second law of friction, and also explain 
one method of determining the co-efficient of friction. 



554 



Steam Engineering 



A block of iron or other metal is drawn across the sur- 
face of the table top by means of weights suspended from a 
cord attached to one end of the blocks and passing over a 
small pulley or roller at one end of the table. The block 
has a flat surface on one side^ while on the opposite side 
there are four small projections or legs^ one on each corner, 
and each leg has a sectional area of one square inch. The 
size of the block may be assumed to be 8 inches wide, 12 
inches long and 2 inches thick, and its weight may be taken 
at 50 pounds. In Figure 222 the block is placed upon the 




Fig. 223 



table with its flat, or largest bearing surface down. This 
surface has an area of 8 inches by 12 inches=96 square 
inches in contact with the surface of the table, and it is 
found that by placing weights on the cord until the block 
begins to move, and keep moving requires a weight of 7 
pounds. Now it might be supposed that if the block were 
reversed so that it would rest on its four legs it could be 
moved across the table with much less weight on the cord 
than was required in the position shown in Figure 222, but 
such is not the case, as shown by Figure 223 and which can 
also be mathematically demonstrated. 



Friction 555 

In the experiment illustrated in Figure 222 the co-efB- 
cient of friction is resistance 7 pounds divided by weight 
or pressure 50 pounds=.14; that is it requires a force of 
14 pounds to move one pound of weight. The pressure 
per square inch of area=weight 50 pounds divided by area 
96 square inches=.52 pounds. The co-efficient being .14 
pounds^ the pull per square inch of surface required to move 
the block is .52 X -14:==. 0729 pounds^ which multiplied by 
the total area 96 square inches equals 6.9888 or practically 
7 pounds. Kef erring to Figure 223 where the block is 
reversed^ and stands on four legs^ each leg having an area 
of one square inch in contact with the surface of the table, 
the total contact is four square inches^ but the pressure re- 
mains the same^ viz., 50 pounds. Therefore the pressure 
per square inch of area=50-^4=12.5 pounds, which when 
multiplied by the co-efficient .14 equals 1.75, which is the 
pull per square inch of surface, and there being 4 square 
inches, the total pull=1.75X4=7 pounds. It will thus be 
seen that the extent of surface in contact does not affect the 
friction so long as the weight or pressure remains constant, 
but by allowing the larger area of surface to come into con- 
tact with the table surface thus distributing the pressure 
over a greater area, reduces the liability of heating and 
abrasion because the pressure per square inch is so much 
less. 

In machine design, especially engine bearings, and crank 
pins, the object should be to obtain as large a surface as 
possible in order that the pressure per square inch may be 
reduced. By making the bearings of proper proportions, 
by using bearing metals having the greatest anti-friction 
value, by keeping the shafting in line, and by the use of 
the best and most suitable lubricants, and lubricating de- 



556 



Steam Engineering 



vices^ or by using self-oiling bearings wherever possible, the 
friction losses may be reduced to a very small percentage 
of the total power developed by the engine. Modern engine 
construction, and methods of lubrication have in recent 
years been brought to such a degree of mechanical refine- 
ment that the friction loss per horse power is only 2 or 3 
per cent. This low per cent of friction loss has been brought 




Fig. 224 



about in the case of high speed engines by properly pro- 
portioning, and balancing the rotating parts, and by the 
use of lubricating apparatus that keeps the bearing con- 
tinuously flooded in a bath of oil. 

Great care should be exercised by the engineer in the 
selection of piston rod, and valve stem packing, and in its 
application and adjustment, as otherwise there will be con- 
siderable friction loss, especially if the packing is unsuit- 



Friction 



557 



able or becomes hard from too long service, or has been 
screwed up too tightly. 

Prof. Chas. H. Benjamin^ in a paper presented at the 
meeting o£ the A. S. M. E. December, 1900, gives the re- 
sults of a series of tests made by himself, at the Case School 
of Applied Science, in Cleveland, Ohio, to determine the 
amount of friction caused by various kinds of piston pack- 
in. Figure 224 shows the device used by Prof. Benjamin in 
making the tests. 

Figure 225 is a sectional view of the same machine, which 
consisted of a cast iron cylinder 6x12 inqhes, fitted at each 




Fig. 225 



end with a suitable head, and stuffing box and gland 
arranged for a two-inch piston rod. The rod was given a 
reciprocating motion, through the medium of a slotted cross- 
head, and crank, and a pulley on the crank shaft was con- 
nected by a belt to a dynamometer. Steam was admitted to 
the cylinder through the pipe shown in Figure 22-1 and the 
water of condensation was drawn off at the bottom, while 
a steam gauge showed the pressure in the cylinder. The 
gland nuts were usually tightened with the fingers only, 
but when a wrench was used, a spring" balance was attached, 
and the turning moment was noted. The stroke of the rod 
was 4.25 inches, and the revolutions were 200 per minute, 



558 



Steam Engineering 



giving a piston speed of 141 feet per minute. Seventeen 
different kinds of packing were nsed^ the materials of which 
were rubber^ cotton^ asbestos, hemp, lead, and flax. 

Some of these packings were combined with mica, graph- 
ite, and paraffine. The various packings were fitted accord- 
ing to the directions of the makers, and the routine of the 
tests as they were conducted was as follows : 

The machine was first run without packing, in order to 
determine the friction of the empty apparatus. The pack- 
ing was then inserted, and steam turned on, the gland nuts 
being tightened just sufficient to prevent leakage, and the 
packing was then tested under various pressures, each test 
lasting from 15 to 40 minutes. The gland nuts were then 
tightened with the wrench, and spring balance to A^arious 
pressures, and other sets of readings taken, after which 



Table 35 









C X* 


rt 








5 


6S 


-osi 




be 




P^ 


.d 


(U 3 




.s 






fcS 






IS 


CO 


O OT 


V 


v> u 




^ 

fu 




if 


w> 




Remarks on Leakage, etc 


o 


H 


'^S 


to <u 


to 

J2 






'o 




2 £ 


Oh"^ 






6 




W 3 


.S 




3 


^ 


H 


< 


ffi 




1 


5 


22 


.091 


.085 


Moderate leakage. 


2 


8 


40 


.049 


.048 


Easily adjusted; slight leakage. 


3 


5 


25 


.037 


.036 


Considerable leakage. 


4 


5 


25 


.159 


.176 


Leaked badly. 


5 


5 


25 


.095 


.081 


Oiling necessary; leaked badly. 


6 


5 


25 


.368 


.400 


Moderate leakage. 


7 


5 


25 


.067 


.067 


Easily adjusted and no leakage. 


8 


5 


25 


.082 


.082 


Very satisfactory ; slight leakage. 


9 


3 


15 


.200 


.182 


Moderate leakage. 


10 


3 




.275 




Excessive leakage. 


11 


5 


25 


.157 


.172 


Moderate leakage. 


12 


5 


25 


.266 


. .380 


Moderate leakage. 


13 


5 


25 


J62 


.230 


No leakage; oiling necessary. 


14 


5 


25 


.176 


.276 


Moderate leakage; oiling necessary. 


15 


5 


25 


.?83 


.255 


Difficult to adjust; no leakage. 


16 


5 


25 


.292 


.210 


Oiling necessary ; no leakage. 


17 


5 


25 


.128 


.084 


No leakage. • 



Friction 



559 



cylinder oil was applied to the rod;, and the difference in 
friction noted. These tests were measured by means of a 
Flather recording dynamometer^ and a Weber box gear 
dynamometer^ the readings being taken at short intervals 
and averaged. The results of these tests are summed up in 
Tables 35 and 36. Table 35 gives a summary of the re- 
sults^ showing the average horse power absorbed by each 
packing at various pressures, and for purpose of compari- 
son, the power at 50 pounds of steam pressure. Table 36 
shows the increased friction caused by tightening the gland 
nuts, and also the beneficial effect of oiling the rod. The 
different packings are numbered. 

The general conclusions arrived at from this series of 
tests are as follows: 

First — That the softer rubber, and graphite packings 
absorb less power in friction than the harder kinds do. 

Second — That oiling the piston rod will reduce the fric- 
tion of any kind of packing. 

Table 36 



oo 






1 






.s 


Horse 


-power Consumed by Each Box, when 1 


H. P. 


Before 


\^ 


Pressure was Applied to Gland Nuts by 


and . 


A.fter 






a 


Seven-inch Wrench 


Oiling Rod. 


a 


5 Lbs. 


8 Lbs. 


10 Lbs. 


12 Lbs. 


14 Lbs. 


16 Lbs. 


Dry 


Oiled 


1 


.120 




.136 












3 








.... 








.055 


.021 


4 






!248 




'.SOS 


.... 


!396 


.154 


.123 


5 






.220 














6 






.348 


.430 








.323 


.194 


7 






.126 


.228 


!266 


'.330 


'M6 


.067 


.053 


8 






.363 


.500 


.535 


.520 


.533 


.533 


.236 


9 






.666 








.... 


.666 


.636 


11 






.405 


'.454 






.... 


.454 


.176 


12 


, . , 




.161 


.242 


!359 


.454 


.... 


.454 


.122 


13 






.317 


.394 


.582 1 






15 






.526 














16 






.327 


.860 












17 






.198 


.277 


.380 











560 Steam Engineering 

Third — That there is almost no limit to the friction loss 
that can be caused by the injudicious nse of the wrench. 

Variations of friction of lubricated surfaces occur with 
every change of condition of either the bearing or journal 
surfaces^ or of the lubricant applied to them. The condi- 
tiv^ns that produce the greatest differences in ordinary lubri- 
cation arC;, the nature and quality of the lubricant^ the 
nature and condition of the wearing surfaces^ and the speed, 
pressure^ and temperature. 

Lubricating Oils. The engineer in charge of a plant will 
always find on the market a wide range of petroleum prod- 
ucts to choose from to meet the various conditions that will 
show up in the proper lubrication of the machinery under 
his charge. The ordinary facilities of the engine room do 
not usually afford means to make elaborate tests of oils, and 
other lubricants, but an engineer can make valuable com- 
parative tests of different grades of oil on his engine, or 
other machinery. 

For instance by means of a thermometer placed in the 
bearing, with the bulb resting on the shaft, or immersed 
in the oil chamber, the temperature of the bearing may 
be noted, while it is being lubricated with various grades 
of oils, and their qualities thus determined. Of course 
in tests of this kind, care should be taken that the rate of 
oil feed, the belt tension, the pressure on the bearings, and 
the speed remain as near constant as possible, and an allow- 
ance should also be made for any difference in the tempera- 
ture of the room during the tests. A good and efficient 
lubricant should possess the following characteristics : 

First, sufficient '^'^body^^ to keep the surfaces apart, but 
the greatest possible fluidity consistent with this. 

Second, a minimum co-efficient of "internaF^ friction in 
actual service. 



Lubrication 561 

Third, must not dry or '^gum/^ and must not contain free 
acids or other corrosive ingredients. 

Fourth, must not be readily thinned^ vaporized or ignited 
by heat^ or stiffened by the cold encountered in the service 
to be performed. 

Fifth, must be absolutely free from all gritty foreign 
substances. 

Sixth, it must be especially adapted to the conditions for 
which it is chosen. 

Experience has proved that in lubrication the best is 
nearly always the cheapest in the end^ and that the consumer 
can better afford to use the highest priced lubricarte the 
market affords^ than accept those of lower value as a gift. 

The cost of lubrication is not merely the market price 
of lubricants^ but their cost plus the cosir^ojthe friction ac- 
companying their use. The value, nt5t the cost, of the lub- 
ricant^ is the point worthy of grea^st consideration. What 
it will do, not tvhat it costs per pound or per gallon. No 
greater error can be made than to economize upon the 
quality of lubricants^ for even under the most extravagant 
conditions the cost of lubricants represents but a very small 
fraction of the cost of fuel, and repairs and depreciation 
of poorly lubricated engines and machinery. 

The best lubricant for a bearing under normal conditions 
may not do so well after heating commences^ a thick viscous 
oil which under ordinary conditions on high speed machin- 
ery would be comparatively wasteful of power is often an 
excellent lubricant for a hot bearing, and for the following 
reason : an engineer on finding a bearing heating up will 
apply the ordinary oil freely^ and at the same time loosen 
up the bolts so as to allow for increased expansion and 
free flow of oil; if the heating continues, and the engine 



562 Steam Engineering 

or machinery must be kept in operation at all hazards^ he 
will turn to his cylinder oil, apply it freely, and often with 
good results. The reason of this is that the cylinder oil, 
owing to its high fire test (from 550 to 600) became thin 
and limpid without burning, and flowed freely between 
the close-fitting surfaces and kept them apart, and at the 
same time, absorbed the heat that would otherwise have 
gone into the metal and carried it away, while the engine 
oil, being of lower flash test, vaporized, and if the bearing 
got hot enough, caught fire. 

In many cases the use of pure graphite or plumbago, as 
it is sometimes called, will prove to be beneficial, especially 
on heavy bearings that are inclined to heat. 

The essential function of graphite is that of an auxiliary, 
or accessory lubricant, with which to perfect and maintain 
the working surfaces in a condition of high polish and great 
smoothness, so that the oils and greases used as the actual 
lubricating film may the more successfully perform their 
particular service. They have only to separate two highly- 
polished and perfectly fitted surfaces and to reduce friction 
to the lowest possible point. 

Graphite allows the safe and satisfactory use of less oil 
or grease than would otherwise be necessary, because there 
is far less actual wearing out of the oil between the smooth 
surfaces. 

Inasmuch as metallic wear is nearly eliminated, the oil 
does not become rapidly charged with fine metal particles 
and lose its lubricating value. 

Thinner lubricants can generally be used. Graphite in- 
creases the endurance and efficiency of oil, and grease lubri- 
cants because it relieves them of a very great part of the 
duty they otherwise have to perform. 



Lubrication 563 

Whether graphite is fed at regular intervals or only 
occasionally the results are much the samC;, inasmuch as 
the coating of graphite persists for a considerable period 
after application. 

In 1902 Professor W. F. M. Goss of Purdue University 
conducted a long series of tests to determine the value of 
Dixon^s Flake Graphite as a general lubricant for bearings, 
and as applied to railroad air brake equipment. 

The tests extended over a period of many months and 
were made, not to create arguments in favor of Dixon's 
Graphite but to enlarge the sum of information on the 
subject of graphite lubrication. 

The following extracts are taken from the report: 

^^From the earlier and rather limited uses of graphite 
in lubrication, the field has gradually widened to include its 
use with light oils, with water, and, in some cases, unmixed 
with other materials. It is no longer regarded merely as a 
material for an emergency, but now has a place in the 
ordinary and usual routine of the engineer's day. . . . 

^^The demand for graphite has come because men charged 
with the responsibility of keeping machinery moving have 
found it beneficial in their work, and not because manu- 
facturers and plant owners pressed its use upon them. 

"It is not to be presumed that because a material is sold 
as graphite it will give good results in lubrication ; it must 
be free from grit and other impurities and properly graded 
for the work. ... 

"Graphite does not behave like oil, but associates itself 
with one or the other of the rubbing surfaces. It is worked 
into every crack and pore in the surfaces and fills them, 
and if the surfaces are ill-shaped or irregularly worn, the 
graphite fills in and overlays until a new surface or more 



564 Steam Engineering 

regular outline is produced. When applied to a well fitted 
journal the rubbing surfaces are coated with a layer so thin 
as to appear hardly more than a slight discoloration. If^ 
on the other hand^ the parts are poorly fitted^ a veneering 
of graphite of varying thickness^ which in the case of a 
certain experiment was found as great as iV inch^ will re- 
sult. The character of this veneering is always the same, 
dense in structure, capable of resisting enormous pressure, 
continuous in service without apparent pore or crack, and 
presenting a superficial finish that is wonderfully smooth 
and delicate to the touch.^^ 

In the lubrication of the interior wearing surfaces of the 
valves, and cylinders of steam engines, conditions will be 
met which are altogether different from those encountered 
in the lubrication of bearings and journals. 

In the latter case, the working and comparing of one oil 
with another, and the results obtained can be easily deter- 
mined by noting the changes of temperature, etc., but in 
internal lubrication, the conditions are altogether different. 

In the case of journals and bearings, the oil can be ap- 
plied directly to the surface to be lubricated; in cylinder 
lubrication one must depend upon the flow of steam to con- 
vey the oil to the parts or wearing surfaces requiring lubri- 
cation. 

The points that govern the conditions of interior lubri- 
cation are : The conditions of the surfaces, the steam pres- 
sure, the amount of moisture in the steam, the piston speed, 
weight and fit of the moving parts, and the make or type 
of the engine. 

An automatic cut off engine with balanced, or piston 
valves will usually require less oil than an engine with a 
heavy unbalanced valve. 



Lubrication 565 

A large cylinder whose piston is supported by a ^'^t ail -rod'' 
is more easily lubricated than one whose heavy piston drags 
back and forth over the bottom of the cylinder. 

An oil to be used as a cylinder lubricant in order to give 
good results must possess certain essential properties. 

It must be of high flash test^ so that it will not volatilize^ 
or vaporize when in contact with the hot steam: it must 
have good viscosity^ or body when in contact with the hot 
surfaces^ and should adhere to^ and form a coating of oil 
80 as to prevent wear and reduce as much as possible the 
friction of the moving parts. 

While the quality of a cylinder oil as shown by the use 
of testing instruments will give one a general idea^ of its 
lubricating value^ the engineer who is studying the question 
of cylindfer lubrication can determine more accurately its 
exact value by experimenting on his engines^ and pumps 
and under the conditions peculiar to his own plant. 

LUBRICATING APPLIANCES. 

Lubricating Appliances. The successful lubrication of 
an engine depends in a large measure upon the character 
of the appliances that are used to convey the lubricant to 
the wearing surfaces. 

For steam cylinder lubrication the hydrostatic^, or sight 
feed type of lubricator is in most general use; this type 
of lubricator depends for its operation upon the displace- 
ment of the oil by a body of water which is formed by the 
<3ondensing of the steam in the condensing chamber of the 
lubricator^ the water in passing into the oil chambers dis- 
places the oil, fo-^cing it up through the sight-feed glass, 
whence it flows through the discharge pipe to the cylinder. 

The construction and operation of this class of lubrica- 



566 



Steam Engineering 



tors will be better understood by reference to Figures 226 
and 227. Figure 226 is an exterior view of the well-known 
Detroit sight-feed lubricator^ while Figure 227 is a sectional 
view showing the interior construction. The pipe P shown 
in Figure 227 connects with a passage from the condenser 
A-2 Figure 226 and when the water feed valve A-4 Figure 




Fig. 226 
exterior view detroit lubricator 



226 is opened^ the water in the condenser will pass down 
the pipe P to the bottom of the lubricator^ and^ being 
heavier than oil, will stay at the bottom, the oil floating 
above it. The pipe S Figure 227 leads from the lower 
sight- feed arm to the upper part of the body of the lubri- 
cator. The action of the lubricator is as follows : 



Lubricating Appliances 



567 



The body A-1 is filled with oil. Steam from the main 
steam pipe passes in the connecting pipes above the lubri- 
cator^ and condenses, filling the condenser A-2 and part of 
the pipe above it with water. The steam also passes into 
the support arm and through the internal tube T into the 
sight-feed glass, where it condenses, filling the glass with 
water. 




Fig. 227 
interior view detroit lubricatob 

As soon as the valve A-4 is opened, the oil in the body 
of the lubricator is subjected to the pressure of the column 
of water extending through the pipe P, the condenser and 
part of the pipe above it, amounting to about 2 pounds to 
the square inch, and in addition to the pressure of the steam 



568 Steam Engineering 

above the water, amounting to say 100 pounds to the square- 
inch, or a total pressure of about 102 pounds to the square 
inch. This we may call the positive pressure. Liquids 
communicate pressure equally in all directions, so the oil 
in the body of the lubricator will press in every direction 
with a force of about 102 pounds to the square inch. It will 
therefore press down through the tube S with this force of 
102 pounds to the square inch. Then, if the valve A-7 is 
opened, a force acting in the opposite direction is en- 
countered, which we may call the back pressure. When 
the lubricator is connected as shown, this back pressure will 
consist of the column of water in the sight-feed glass, and 
in addition, the steam pressure back of this column entering 
through the support arm, and amounting to 100 pounds to 
the square inch. 

The positive steam pressure being just the same as the 
back steam pressure, these two forces will neutralize each 
other, and we have left, the positive pressure of the column 
of water extending through the pipe P, the condenser and 
part of the pipe above it, and the back pressure of the 
column of water in the sight-feed glass. As the latter is 
much less than the positive pressure, the drop of oil is forced 
through the nozzle. As soon as it leaves the nozzle it is 
no longer acted upon by the positive pressure, and it rises 
through the water in the glass from the force of gravity, it 
being lighter than the water. After rising through the- 
sight-feed glass it floats through the tube T, Figure 227,. 
and through the support arm into the main steampipe and 
goes with the current of steam to the steam chest and 
cylinder. The positive pressure must always be greater than 
the back pressure, or the lubricator will not work. 

For instance, if a lubricator be connected to a horizontal 
steampipe by being suspended below it, the back pressure- 



WOl 



Lubricating Appliances 



,569 



ould be greatly increased^ and in order to get sufficient 
positive pressure the condensing pipe should rise 18 inches 
to 24 inches above the horizontal steampipe and then de- 
scend to the condenser. This will give a column of water 
for positive pressure higher than the column of water 
which acts as back pressure. 



TO RE-FILL AND OPERATE. 



Close valves A-4 and A-7. Open drain valve A-8^ then 
remove filler plug A-3 and the water will drain out rapidly. 



.fER VALVE 
^ FiLUN^CAP 




^REfiUtATINQV/aVE 

Fig. 228 
powell lubricator 
A, Oil reservoir. B, Fining cup. C, Valve to regulate oil 
drops. D, Shut-off valve. E, Packing nuts. F, Drain valve. 
H, coupling for condensing pipe. JJ, Sight feed and index 
glasses. K, Plug for removing and inserting glasses. M, Con- 
densing chamber. N, Valve to regulate water from the con- 
denser. V, Valve to drain sight feed glass. R, Attachiiig shank 
and valve. 



570 



Steam Engineering 



When water is all out;, close valve A-8^ fill with oil^ and re- 
place filler plug A-3. Then open valve A-4, and regulate 
the flow of oil with valve A-7. The valve A-9 is to be 
closed only when desiring to shut off steam from the lubri- 
cator in case of accidental breakage of the giass^ or when 
there is danger from freezing. Before starting the lubri- 
cator, time should be allowed for the sight-feed glass, and 




FiG.^229 
Powell's duplex condenser locomotive lubricatob 

condensing chamber to fill with water from condensation. 
When there is danger from freezing when lubricator is not 
in use, empty the lubricator, and leave open valves A-4, 
A-8 and A-6. Then close valve A-9 and the small angle 
valve in condensing pipe above the lubricator. 

Figure 228 shows an external view of the Powell lubri- 
cator "Class A/^ for single cylinder engines, and Figures 



Lubricating Appliances 



-571 



■329 and 230 show exterior, and sectional views of the 
Powell duplex condenser and double, up-feed lubricator for 
filiuse on compound and triple expansion engines. In this 
lubricator there may be two or three sight- feeds combined 
with one oil chamber. The letters designate the different 
parts, and the operation of this lubricator will be easily 
understood by a study of Figure 230. 




Fig. 230 
description of internal parts 
A, Oil chamber. CC, Oil drop regulating valves. EE, Brass 
protecting shields. F, Drain valve. GG, Removable plugs tb 
clean oil tubes. HH^ Packing nuts. II, Adjustable rings. 
JJ, Sight glasses. I^K, Removable cages to replace glasses. 
MM", Condensers. N, Water valve. T, Connecting coupling to 
boiler. W, Cleaning valves for sight g-lasses. W, Water tube. 
X, Water and oil trap. 



572 



Steam Engineering 



The force feed^ or mechanically operated lubricator, has 
come into favor largely within recent years, and it certainly 
has the merit of being positive, while at the same time it is 
not wasteful of oil, being governed by the speed of the en- 
gine or pump that it is lubricating. This type of lubricator 
is made in single, double, triple, and quadruple style, and 
is operated by attaching the connecting rod of the oil pump 




Fig. 231 
manzel quadruple feed, oil pump 

to any movable part of the engine that will give it a recipro- 
eating motion. 

Figure 231 shows the Manzel quadruple feed oil pump. 
These pumps are also made with five and six feeds. Man- 
zel Brothers Co. also make an agitating force, and sight- 
feed oil pump for the purpose of feeding graphite mixed 
with the oil. Graphite being a mineral and not easily sus- 
pended in oil it has always been a rather difficiilt problem 



Lubricating Appliances 



573 



to feed it properly along with the oil^ but the device illus- 
trated in Figure 232 has proved to be very successful in 
feeding the mixture of oil and graphite. The action of this 
appliance will be easily comprehended by a reference to 
Figure 232. The spiral agitating device that revolves in 
the cup is operated by means of the belt-drive on the wheel. 




Fig. 232 
the manzel agitating, force and sight feed oil pump 

land bevel gears on the cup. The construction is simple 
and durable. Two fillers are used^ one for oil and one for 
graphite. No fixed rule can be laid down for the amount 
of graphite to be used, as some engines require more than 
others. Two or three good teaspoonfuls to a pint of valve 
oil, would be a good rule to start on, and the engineer can 



574 Steam Engineering 

then watch resnlts and ascertain for himself the proper 
quantity to use. 

Another rule might he^ three teaspoonfuls of graphite 
per day for a 150 horse power engine. 

To Attach the Manzel Oil Pump. Place the pump on 
the frame of an engine^ or pump where it is most conven- 
ient to get motion. It can be bolted to a stud or stand. 
Attach connecting rod of the pump to any movable part 
that travels back and forth such as a valve rod to an en- 
gin€^ or rocker arm of a pump. Connect the pipe to the 
pump cylinder. Use Vs i^ch pipe for % pint and pint 
pumps^ and 14 i^ch pipe for all other sizes; the end of 
pumps and check valves are threaded for these sizes^ and 
run tOy and enter the steam line or steam chest above or 
below the throttle^ as desired. Equip the oil pipes as near 
as possible to the steam line with check valve; the end 
marked ^^S^^ toward the steam line. By using a reducer^ % 
inch pipe can be used on the larger size pump. 

The feed on the "Maxzel Improved'' Pump is regulated 
while in operation on the engine^ on the upper plungers. 
To increase the feed^ screw plunger inward^ to decrease the 
feed^ screw plunger outward^ then tighten lock-nut. Partic- 
ular attention is called to the regularity of the feed that is 
obtained on these pumps under all conditions. They can 
be regulated to feed from nothing or one drop to a stream of 
oil with every stroke of the plunger. 

Another good force feed lubricator is the Dietz high 
pressure force feed lubricator made by the Pearl Manu- 
facturing Co. of Buffalo^ New York. This device is made 
either single^ or double actings and with from one to six 
feeds. 

Figure 233 shows a double acting three-feed Deitz high 
pressure lubricator, and it is claimed by the manufacturers 



Lubricating Appliances 575 

that it will feed any mixture of oil and graphite without 
becoming clogged^ owing to the fact that the valves are of 
the poppet typC;, and made of steely and when not opened 



Fig. 233 

DIETZ HIGH PRESSURE FORCE FEED LUBRICATOR 

by the cams^ are held to their seats by a strong spiral spring 
in addition to the pressure. This oil pump is fitted with a 
cranky by means of which it may be worked by liand, in 
starting^ or should an extra amount of oil be required at 



576 



Steam Engineering 




Fig. 234 
rochester force feed lubricator with monitor sight feed 

appliance 

any time. The pump is driven in the usual way by con- 
necting to the valve rod of the engine and the feed is 
regulated by varying the travel of the rocker arm. 

Figure 234 shows the Eochester force feed lubricator^ 
as it appears with the Monitor sight-feed attachment 



Lubricating Appliances 577 

screwed onto the delivery pipe^ by means of which the engi- 
neer is enabled to see the drops of oil as they are being fed 
to the cylinder or bearings. The number and size of the 
drops can be regulated to suit the requirements of the 
engine. 

QUESTIONS AND ANSWERS. 

423. What is one of the most important problems con- 
nected with engine operation ? 

Ans. The proper lubrication of the bearings. 

424. What is friction ? 

Ans. The resistance caused by the motion of a body in 
contact with another body that does not partake of its 
motion. 

425. What is the first law of friction? 

Ans. Friction varies in proportion to the pressure on 
the surfaces in contact. 

426. Define the second law of friction. 

Ans. Friction is independent of the areas of surface in 
contact. 

427. What is the third law of friction? 

Ans. Friction increases with the roughness of the sur- 
faces^ and decreases as the surfaces become smoother. 

428. What is the fourth law of friction? 

Ans. Friction is greatest at the beginning of motion. 

429. Give the fifth law of friction? 

Ans. Friction is greater between soft bodies than it is 
between hard bodies. 

430. When, and by whom were these laws first formu- 
lated? 

Ans. In 1831-33 by Gen. Arthur Morin, a French en- 
gineer. 



578 Steam Engineering 

431.. What is the tendency of friction with machinery 
in operation? 

Ans, It tends to cause the parts to adhere to each other. 

432. How may this friction be largely obviated? 
Ans, By proper lubrication of the rnbbing surfaces. 

433. Does friction serve any good purpose? 

Ans. Yes^ for instance the friction of the belt in con- 
tact with the rim of the pnlley^ also the friction of the 
driving wheels of a locomotive. 

434. How many kinds of friction are there in connec- 
tion with machinery in operation ? 

Ans. Two^ viz.^ the friction of solids^ and the friction 
of liquids. 

435. What is meant by the term co-efRcient of friction? 
Ans. The ratio of the power required to move a body, 

and the pressure on that body. 

436. What should be the object sought in the design 
of engine bearings? 

Ans. To obtain as large. a rubbing surface as possible. 

437. Mention some of the qualities that a good lubri- 
cating oil should possess. 

Alls. It should have a good ^^body^^ — must not dry or 
^^gum f^ must not be easily thinned by heat, or thickened by 
cold. Must be free from all gritty substances. 

438. What is the proper kind of oil to use on a bearing 
that has started to heat ? 

Ans. Cylinder oil, owing to its high fire test. 

439. Is graphite, or plumbago a good lubricant? 
Ans. It is in many cases. 

440. What is the essential function of graphite ? 
Ans. It is an auxiliar}^, or accessory lubricant. 

441. Mention some of the points that govern interior 
lubrication of engine parts. 



Questions and Answers 579 

Ans, The conditions of the surfaces ; the steam pressure ; 
the amount of moisture in the steam ; piston speed ; weight, 
and fit of moving parts, etc. 

442. What properties should a good cylinder oil possevss? 
Ans. It must be of high flash test; must have good 

viscosity, or body when in contact with hot surfaces. 

443. Upon what does the successful lubrication of an 
engine largely depend? 

Ans, Upon the character of the lubricating appliances 
used. 

444. What system of lubrication for cylinders, and 
valves is most largely used? 

Ans. The hydrostatic, or sight-feed type of lubricator. 
' 445. What other system has come into extensive use in 
late years? 

Ans. The force feed, or mechanically operated oil pump. 



The Steam Turbine 

Althoiigh the turbine principle of utilizing the heat 
energy in steam and converting it into useful work has 
been experimented upon for many years^ it is only since 
the inauguration of the twentieth century that steam tur- 
bines have been brought to the front as efficient power 
producers. 

The piston of the reciprocating engine is driven back 
and forth by the static expansive force of the steam^ while 
in the steam turbine not only the expansive force is made 
to do work, but a still more important element is utilized, 
viz., the kinetic energy, or heat energy latent in the steam, 
and which manifests itself in the rapid vibratory motion of 
the particles of steam expanding from a high, to a low 
pressure, and this motion the steam turbine transforms 
into work. 

Xotwithstanding the fact that much has been said and 
written during the past four years regarding the steam 
turbine, the machine is to-day a mystery to thousands of 
engineers, not because they do not desire information upon 
the subject, but because of a lack of opportunities for ob- 
taining that information. The author therefore considers 
tliat a space devoted to this subject would no doubt be of 
benefit to his readers. 

The steam turbine is simple and compact in design, hav- 
ing few working parts as compared with the reciprocating 
engine, and any engineer who is capable of operating and 
caring for an engine of the latter type, can also run and 
take care of a steam turbine. But, as in the case of the 

581 



582 



Steam Engineering 




Fig. 235 
four westinghouse-parsons steam turbines 



The Steam Turhine 



583 



reciprocating engine^ the engineer in charge of a turbine 
plant should be familiar with the interior construction of 
the machines under his charge^, and he should know what 
to do^ and what to avoid in order to keep them in continual 
and efficient operation. 




Fig. 236 

The steam turbine in principle^ and even in type is not 
new^ being in fact the first heat motor of which we have 
any record in steam engineering. 

One of the earliest descriptions of a device for convert- 
ing the power of steam into work was recorded by Hero, 
a learned writer who flourished in the city of Alexandria 



584 



Steam Engineering 



in Egypt^ in the second century before Christ. Hero de- 
scribes a machine called an Aeolipile or ^^Ball of Aeolus/^, 
illustrated in Pig. 236. B is the boiler under which a 
fire was made. G is a hollow metallic globe that revolved 
on trunnions C and D^ one of which terminated in a pivot 
at E^ while the other was hoUoviT and conveyed the steam 
generated in the boiler B to the interior of the globe or 
ball;, from which it escaped through the hollow bent tubes 
H and I^ and the reaction of the escaping steam caused the 




Fig. 237 

globe to revolve. This was the first steam turbine, and 
it worked on the reaction principle. 

Many centuries later, in the year A. D. 1629, Branca, 
an Italian, described an engine which marks a change in 
the method of using the steam. Branca^s engine consisted 
of a boiler A, Fig. 237, from which the steam issued through 
a straight pipe, and impinged upon the vanes of a hori- 
zontal wheel carried upon a vertical shaft, causing it to 
revolve. This device was the germ of the impulse tur- 



The Steam Turbine 585 

bine^ and these two principles, viz., reaction and impulse, 
either one or the other, and sometimes a combination of 
both, are the fiindamentarprinciples upon which the suc- 
cessful steam turbines of the present age operate. 

Steam expanding through a definite range of tempera- 
ture and pressure exerts the same energy whether it issues 
from a suitable orifice or expands against a receding piston. 

Two transformations of energy take place in the steam 
turbine; first, from thermal to kinetic energy; second, 
from kinetic energy to useful work. The latter alone pre- 
sents an analogy to the hydraulic turbine. 

The radical difference between the two turbines lies in 
the low density of steam as compared to water, and the 
wide variation of its volume under varying temperatures 
and pressures. 

A cubic foot of steam under 100 lbs. pressure, if allowed 
to discharge into a vacuum of 28 inches, would attain a 
theoretical velocity of 3,860 feet per second and would 
exert 59,900 ft. lbs. of energy. 

A law of turbo-mechanics specifies that in order to ob- 
tain the highest efficiency in the operation of turbines 
(whether water or steam) the relation between bucket 
speed and fluid speed, (steam in this case), should be as 
follows : 

For purely impulse wheels, bucket speed equals one-half 
of jet speed. 

For reaction wheels, bucket speed equals jet speed. 

Assuming the velocity of the jet of steam issuing from 
the nozzle to be 4,000 feet per second, this would mean 
a peripheral speed of 2,000 feet per second for an im- 
pulse wheel, and for a wheel 1 foot in diameter the speed 
would be 38,100 E. P. M. But such a speed is beyond 



586 



Steam Engineering 



the limits of strength of material^ and the speed of steam 
turbines is accordingly kept within the bounds of safety, 
and strength of material. 

Form of Blade. — The blades or buckets should be of 
such form^ and curvature as will permit the steam to ex- 
pand to the desired final^ or terminal pressure with the 
smallest possible friction and eddy current losses. As to 
directing the flow in the desired course, the direction of 

1^^ ^ d 




Fig. 238 



exit from the guide, and rotating wheel is of the greatest 
importance. In order to get the desired angle, the last 
part of the blade should be kept straight, at least to the 
foot of the perpendicular dropped from A^, or the length 
A B in Fig. 238. Prom there on, the channel should lead 
in easy curvature to the angle a^. The construction ac- 
cording to a in Fig. 238 would obviously be too sharp, and 
would cause the steam stream to separate from the wall. 



The Steam Turbine 587 

The constmction according to b would suffice^ and the 
wheel radius would depend, above all, upon how far we 
wish to diminish the shock at entrance. For the profile b 
the angle a^ is taken as the slope of the blade back, from 
which we obtain for the guiding blade surface the some- 
what large angle a^'. This would be more favorable with c, 
and d, but the latter would obviously give a needlessly 
long steam path. Besides, a pointing of the blade such 
that a-L is half of a^', as is shown dotted at d, could be con- 
sidered just as correct as the first mentioned. By drawing 
the absolute steam path and finding the decrease of peri- 
pheral speed, we get useful results concerning the regu- 
larity of delivering work. 

The proper length of the channel, or steam path can 
only be determined by practical experience, and with a 
given curvature the ratio of length to breadth can be con- 
sidered fairly constant. 

Stuffing Boxes. — The stuffing boxes are the most im- 
portant and delicate part of the steam turbine. As they 
are subjected to high temperature on account of their 
proximity to the steam space, the problem of getting rid of 
their own heat of friction becomes all the more difficult. 
The advantage of the stuffing box used on reciprocating 
engines, where the rod for part of the time is exposed to 
the air, and cools at least its surface by radiation, cannot 
be considered with the rotating shaft. Water-cooling may 
be an effective means, but creates considerable loss by con- 
densation in the surrounding steam spaces. 

The majority of designers get around this difficulty by 
avoiding contact between packing and shaft, and secure 
tightness only by the least possible clearance. This is the 
principle of the so-called "labyrinth stuffing box^' that was 



588 



Steam Engineering 



first generally used by Parsons. This is shown in Fig. 
239, in which A is the shaft, B the stuffing box. The rings 




y -^ y 

Fig. 239 
labarynth stuffing box 



on both parts form alternately a narrow space x, and a 
large space y. The velocity of the steam flowing through 
this narrow space is destroyed by eddy-currents in the 




Fig. 240 



Fig. 241 



large space, so that for further velocity, a part of the drop 
in pressure is utilized. With a large number of rings, 
and with very small spaces x; the loss is greatly decreased. 



The Steam Turbine 



589 



It also seems to have a favorable influence when the steam 
in leaving this narrow space flows radially inwards^ that is, 
it helps to overcome its centrifugal force. 

Fig. 240 shows the stufling box of a Sckulz turbine, ISTo 
provision is here made for enlarged spaces^ but the neces- 
sary throttling is accomplished by the great length of the 
labyrinth path. The designer hoped to limit his clearance 
to 1 mm. (0.039 in.). The outer box is made in two parts. 




Fig. 242 



Fig. 241 shows a stufiing box by the same designer^ built 
of rings^ in which the inner rings are loose, but are made 
with a neat fit. 

The Eateau stuffing box is shown in Fig. 242. The 
main part consists of the shaft, a, enclosed by a close fit- 
ting box b, of suitable metal. The steam leaking through 
this space flows into chamber c, where a constant pressure 
of about 12 lbs. absolute is maintained by a reducing valve. 
From the valve the steam is led to a condenser. Chamber 
c, is kept steam tight from the outside by two bronze rings 



590 



Steam Engineering 



d^ d;, each made in three parts^ which are held against the 
shaft with slight pressure by the spiral springs e. A pres- 
sure in an axial direction is caused by springs f. The 
chambers of all the stuffing boxes of the turbine are con- 
nected together. Thus a portion of the steam that leaves 
the high pressure chamber will be drawn into the low pres- 
sure side. When running lights partial vacuum exists in 
all the stuffing boxes^ the reducing valve allowing live 




Fig. 243 

steam to enter^ thus preventing air from being drawn in. 

Steam is led in Figs. 240 and 241 through the ring 
passages^ and excludes thereby the air, so that the vacuum 
does not suffer. 

The construction of a turbine stuffing box as steam tight 
as that of the steam engine is still an unsolved problem. 
For this reason we might add the excellent stuffing box of 
Schwabe^ that is used in steam-engine work, shown in 
Fig. 243. This consists of a large number of rings D 



The Steam Turbine 591 

made in three parts^ held together by a circumferential 
spiral spring. These rings (for the steam engine) press 
on one another^ and should either not touch the shaft at 
all^ or with only the slightest pressure.- With turbines/ the 
soft packing at the outer end will of course be omitted, 
and the rings must be prevented from turning, and so con- 
structed as to be tight against either pressure or vacuum. 
The inside and outside ends of the box are provided with 
means for oiling. 

The Regulation of the Steam Turhine. — The regulation 
in the majority of different systems is acomplished by sim- 
ple throttling, thus decreasing, at the very beginning, the 
available work of the steam, and consequently the economy 
of the turbine. The loss is measured by the product of the 
increase of entropy and the absolute temperature of the 
exhaust steam, which can easily be determined from the 
entropy tables. 

The ideal conditions would be to constantly work with a 
full initial pressure, and to make all cross-sections of steam 
passages suitable to the power required. Constructively, 
this idea, is most easily applicable to the single stage im- 
pulse turbine, in which the nozzles are opened or closed one 
after another by means of a regulator. 

The following description of the construction, and prin- 
ciples controlling the action of the leading types of steam 
turbines manufactured in the United States is presented, 
with the hope that it may prove to be not only interesting, 
but instructive as wfell, to the student. 

It may be said in general of the steam turbine, that it 
has passed the experimental stage, and has come to the 
front as an efficient power producer, having a bright 
future before it. It has solved the problem of using super- 



592 Steam Engineering 

heated steam, owing to the absence of all rubbing parts 
exposed to the steam. This permits the use of steam of 
high temperature, thus making it possible to realize the 
advantages of economical operation. 



The Westinghouse-Parsons Steam 
Turbine 

The W estinghouse-P arsons Steam Turbine operates on 
both impulse and reaction principles^ and by a system of 
compounding^ which will be explained later on^ the peri- 
pheral velocity of the machine has been so reduced as to 




Fig. 244 

bring it within practical limitS;, while at the same time the 
power value of the steam is utilized to a high degree of 
efficiency. 

The speed of the Westinghouse-Parsons turbine varies 
from about 750 R. P. M. for a 5,000 K. W. machine, to 
3,600 E. P. M. for a 400 K. W. turbine. 

593 



594 Steam Engineering 

The Westinghonse-Parsons turbine is fundamentally 
based upon the invention of Mr. Charles A. Parsons, who^ 
while experimenting with a reaction turbine constructed 
along the lines of Hero's engine^ conceived the idea of 
combining the two principles^ reaction and impulse, and 
also of causing the steam to flow in a general direction 
parallel with the shaft of the turbine. This principle of 
parallel flow is common to all four types of turbines, but 
is perhaps more prominent in the Westinghouse-Parsons^ 
and less so in the De Laval. 

Fig. 235 shows a general view of four Westinghouser 
Parsons steam turbines^ and Pig. 244 shows a 600 H. P. 
machine with the upper half of the cylinder^ or stator as it 
is termed, thrown back for inspection. Fig.. 245 is a sec- 
tional view of a Westinghouse- Parsons turbine^ and it will 
be noticed that there are three sections or drums^ gradually 
increasing in diameter from the inlet A, to the third and 
last group of blades. This arrangement may be likened 
in some measure to the triple compound reciprocating 
engine. 

Fig. 246 shows the complete revolving part of a 3^000 
H. P. turbine. Its weight is 28,000 lbs., length over all 
19 feet 8 inches, and 12 feet 3 inches between bearings; 
the largest diamater, 6 feet. 

By reference to Fig. 244 it will be seen that the inside 
of the cylinder is stud.ded with rows of small stationary 
blades, and that the rotor or revolving part of the ma- 
chine is also fitted with rows of small blades, similar in 
shape and dimensions to the stationary blades. "WTien the 
upper half of the cylinder is in position, each row of sta- 
tionary blades fits in between two corresponding rows of 
moving blades. This arrangement may perhaps be better 



Westinghouse-Parsons Steam Turbine 595 




Fig. 245 

SECTION OF STANDARD WESTINGHOUSE SINGLE FLOW TURBINE 



596 Steam Engineering 

understood by reference to Fig. 247^ which illustrates the 
relation of the stationary blades to the moving blades when 
in position^ and also shows by the arrows the course of the 
steam and its change of direction caused by the stationary 
blades. 

For the purpose of explanation the moving blades or 
vanes may be considered as small curved paddles pro- 
jecting from the surface of the rotor^ and there is a large 
number of them^ as for instance, taking a 400 K. W. ma- 
chine, there are 16,095 moving blades and 14,978 sta- 
tionary blades, a total of 31,073. 




Fig. 246 

The stationary vanes, as previously explained project 
from the inside surface of the cylinder. Both stationary 
and moving vanes are similar in shape, and are made of 
hard drav/n material, and they are set into their places 
and secured by a caulking process. The blades vary in size 
from 1^ to 7 in. in length, according to where they are 
used. Eeferring to Fig. 244, it will be observed that the 
shortest blades are placed at what might be termed the 
steam end of each section or drum of the rotor and cylinder, 
and that their length gradually increases, corresponding 



W estinghouse-P arsons Steam Turbine 597 

with the increased volume of steam^ until a mechanical 
limit is reached;, when a new group of blades begins on a 
succeeding drum of larger diameter. Eeferring to Fig. 
247;, which is a sectional view of four rows of blades^ it will 
be noticed that all the blades^, whether stationary or mov- 
ing;, have the same curvature. Also that the curves are set 
opposite each other. The reason for this will be apparent 
as the diagram is studied. The steam at pressure P first 
comes in contact with row 1 of stationary blades. It 
expands through this row^ and in expanding the pressure 
falls to P'. 

CCvCCCCCC ^"T^ATIOhlARY BLADES 

)) )) )) })1:D D D D MOVmS BLADES 
rCCCCCCCC STATIONkRY BLADES 



Fig. 247 



MOVING BLADES 



The energy in the steam is converted into velocity^ and 
it impinges upon row 2 of moving blades^ driving them 
around in their course by impulse, A second expansion 
now occurs in row 2^ and again the energy is converted into 
velocity^, but this time the reaction of the steam as it leaves 
the blades of row 2 also tends to impel them around in 
their course. The moving blades thus receive motion from 
two causes — the one due to the impulse of the steam strik- 
ing them^, and the other due to the reaction of the steam 
leaving them. 



598 Steam Engineering 

This cycle is repeated in rows 3 and 4^ and so on through- 
out the length of the rotor until the exhaust end is reached. 

It should be noted that the general direction taken by 
the steam in its passage through the turbine is in the form 
of a spiral or screw line about the rotor. The clearance* 
between the blades as they stand in the rows is % in. for 
the smallest size blades and ^2 i^i- for "the larger ones, 
gradually increasing from the inlet to the exhaust. In the 
5^000 K. W. machine the clearance at the exhaust end be- 
tween the rows of blades is 1 in. It will thus be seen that 
there is ample mechanical clearance, also allowance for 
lateral motion for adjustment of the rotor, although this is 
very slight, as the -rotor is balanced at all loads and pres- 
sures by the balancing pistons PPP, Fig. 245, to which 
reference is now made. These pistons revolve within the 
cylinder, but do not come in mechanical contact with it; 
consequently there is no friction. The diameter of each 
piston corresponds to the diameter of one of the three' 
drums. 

The steam entering the chamber A through valve V 
presses against the turbine blades and goes through doing 
work by reason of its velocity. It also presses equally in 
the opposite direction against the first piston P, and so 
the shaft or rotor has no end thrust. On leaving the first 
group of blades and striking the second group the pressure 
in either direction is again equalized by the balance port 
E allowing the steam to press against the second balance 
piston P. The same event occurs at group three, the 
steam acting upon the third piston P. 

The areas of the balancing pistons are such that, no 
matter what the load may be, or what the steam pressure 
or exhaust pressure may be, the correct balance is main- 



I 



Westinghouse-Parsons Steam Turbine 599 

tained and there is practically no end thrust. Below is 
shown a pipe E connecting the back of the balancing pis- 
tons with the exhaust chamber. This arrangement is for 
the purpose of equalizing the pressure at this point with 
the pressure in the exhaust chamber. 

It might be thought that the blades^ on account of their 
being so light and thin^ would wear out very fast^ but ex- 
perience so far shows that they do not. This may be ac- 
counted for in two ways. Firsts the reduction of the 
velocity of the steam, the highest velocity in the Parsons 
turbine not exceeding 600 ft. per second; secondly, the 
light steam thrust on each blade, said to be equal to about 
1 oz. avoirdupois. This is far within the bending strength 
of the material. A steam strainer is also placed in the 
admission port, to prevent all foreign substances from en- 
tering the turbine. 

A rigid shaft and thrust or adjusthient bearing accu- 
rately preserves the clearances, which are larger in +his 
turbine than in other types, owing to the fact that the 
entire circumference of the turbine is constantly filled 
with working steam when in operation. 

The bearings shown in Pig. 245 are constructed along 
lines differing from those of the ordinary reciprocating 
engine. The bearing proper is a gun metal sleeve, see Pig. 
248, that is prevented from turning by a loose-fitting 
dowel. Outside of this sleeve are three concentric tubes 
having a small clearance between them. This clearance is 
kept constantly filled with oil supplied under light pres- 
sure, which permits a vibration of the inner shell or sleeve 
and at the same time tends to restrain or cushion it. This 
arrangement allows the shaft to revolve about its axis of 
gravity, instead of the geometrical axis, as would be the 



600 



Steam Engineering 



case if the bearing were of the ordinary construction. The 
journal is thus to a certain degree a floating journal, free 
to run slightly eccentric according as the shaft may hap- 
pen to be out of balance. 




Fig. 248 

A flexible coupling is provided, by means of which the 
power of the turbine is transmitted to the dynamo or other 
machine it is intended to run. The oil from all the bear- 



Westinghouse-Parsons Steam Turbine 601 

ings drains back into a reservoir^ and from there it is forced 
up into a chamber, where it forms a static head, which 
gives a constant pressure of oil on all the bearings. A 
secondary valve is located at Vs, by means of which high 
pressure steam may be admitted to the steam space E on 
the same principle that high pressure steam is admitted to 
the low pressure cylinder of a compound engine. This 
valve opens automatically in cases of emergency, such as 
overload, failure of the condenser to work, etc. 

The shaft, where it passes through either cylinder head, 
is packed with a water seal packing, consisting of a small 
paddle wheel attached to the shaft, which, through centri- 
fugal action, maintains a static pressure of about 5 lbs. per 
sq. in. in the water seal, thus preventing all leakage while 
at the same time it is frictionless. 

. Governor, — The speed of the Westinghonse-Parsons tur- 
bine is regulated by a fly ball governor constructed in such 
manner that a very slight movement of the balls serves to 
produce the required change in the supply of steam. Fig. 
249 is a diagram of the governor mechanism. The ball 
levers swing on knife edges instead of pins. The gover- 
nor works both ways, that is to say, when the levers are 
oscillating about their mid position a head of steam corre- 
sponding to full load is being admitted to the turbine, and 
a movement from this point, either np or down, tends to 
increase or to decrease the supply of steam. 

Eeferring to Fig. 249,, B is a piston directly connected 
to the admission valve. Steam is admitted to this piston 
under control of the pilot valve A, which has a slight but 
continuous reciprocating motion derived from the eccentric 
rod C, and the function of the governor is to vary the plane 
of oscillation of this valve, thus causing it to admit more 



602 



Steam Engineering 



or less steam to piston B. The admission valve, being 
actuated exclusively by piston B, is thus Gatised to remain 
open for a longer or shorter period of time/ according to 
the. load upon th^ turbine. 

'^The vibrations of the admission valve, although very 
slight, are continuous and regular, about 165 per minute, 
and are transmitted primarily by means of an eccentric, 
the rod of which is shown at C, Fig. 249. 




Fig. 249 



The governor sleeve is used as a floating fulcrum, and 
the points D and E are fixed. By means of this very 
ingenious device the steam is admitted to the turbine in 
puffs, either long or short, according to th6 demand for 
steam. At full load the puffs merge into an almost con- 
tinuous blast. When the load has increased to the point 
where the valve is wide open continuously, a full head of 
steam is being admitted. Beyond this the secondary valve 
comes into action, thus keeping the speed up to normal. 



W estingJiouse-F arsons Steam Turbine 



603 



The rotor requires perfect balancing to ihsnre quiet 
runnings but this is easily accomplished in the shop by 
means of a balancing machine used by the builders. 

Steam turbines generally show higher efficiency in the 
use of steam than reciprocating engines do^ and this fact 
is due. to three leading causes. First^ it is possible with 
the turbine to use highly superheated! steam which, owing 
to the difficulties attending lubrication^ could not be used 
in the* reciprocating engine. Second^ a larger proportion of 
the heat contained in the steam is converted into work, for 




Fig. 250 
new blading jviateeial 

the reason that the steam is allowed to expand to a much 
lower pressure^ and into a higher vacuum. In addition to 
this^ the velocity of the expanding steam is utilized in a 
much higher degree in the turbine as compared with the re- 
ciprocating engine. Thirds mechanical friction or lost 
work is reduced to the minimum. Under test a 400 K. W. 
Westinghouse-Parsons steam turbine^ using steam at 150 
lbs. initial pressure and superheated about 180°, consumed 
11.17 lbs. of steam per brake horse power hour at full load. 
riie speed was 3,550 E. P. M. and the vacuum was 28 in. 



604 Steam Engineering 

With dry saturated steam the consumption was 13.5 lbs. 
per B. H. P. hour at full load^ and 15.5 lbs. at one-half 
load. 

A 1^000 K. W^. machine, using steam of 150 lbs. pres- 
sure and superheated 140°, exhausting into a vacuum of 
28 in., showed the very remarkable economy of 13.66 lbs 
of steam per E. H. 1^. per hour. 

A 1,500 K. W. Westinghouse-Parsons turbine, using dry 
saturated steam of 150 lbs. pressure with 27 in. vacuum, 
consumed 14.8 lbs. steam per E. H. P. hour at full load, 
and 17.2 lbs. at one-half load. 

The Westinghouse machine company have recently in- 
troduced a new blade material which is now used in all 
Westinghouse turbines. It is a copper-coated steel blade, 
or, as designated by the builder, "Monnot metaU^ in which 
the copper coating (seen in Fig. 250) is chemically welded 



to I 



to the steel so thoroughly that the blades can be drawn 
the desired shape from the original ingot, without weaken- 
ing the union between the copper and steel. The process 
of drawing makes the copper coating somewhat thicker at \ 
the inlet and outlet edges of the blade, though the remain- 
ing portions of the blade surfaces are coated with an abso- 
lutely uniform thickness of copper. The only portion of 
the blade where steel is exposed, is the small surface of the 
tip of the blade where, however, corrosion is the least detri- 
mental, for should the tips corrode, the copper coating 
would still remain intact, thus leaving the working blade 
surfaces untouched and the blade clearances unaltered. 

Figs. 251 and 252 show sectional elevations of the double 
flow type of steam turbines now being manufactured by the 
Westinghouse company, in addition to the standard single 
flow turbine already described. 



Westinghouse-Parsons Steam Turbine 605 




Fig. 251 
section of westinghouse double flow turbine 



606 



Steam Engineering 




Fig. 252 

westinghouse double flow low-pressure turbine 

Siectional Elevation 

Pig. 251 shows the machine as adapted for using steam 
■oi high initial pressure, in fact an impulse turbine, in which 
the steam admitted first to the nozzle block, is expanded 



Westinghouse-Parsons Steam Turbine 607 

in nozzles arranged about the periphery^ and impinges 
upon the impulse buckets of the central rotation wheel. 
There are two rows of moving blades upon the impulse 
wheel^ with an intermediate set of reversing blades as 
shown. Issuing from the delivery side of this wheel with 
its velocity energy practically all abstracted, the steam 
passes, as shown by the arrow, to an intermediate set of 
Parsons blading. As this blading has no counterpart upon 
the other side of the turbine, the pressure upon it must be 
counterbalanced, and this is done by making the extension 
of the hub by which the impulse wheel is keyed to the shaft, 
into a piston or dummy of the mean diameter of the inter- 
mediate stage, as shown at P. After passing the inter- 
jnediate stage the steam divides, one portion passing 
directly to the low-pressure blading at the left, while the 
rest passes through the hollow shell of the rotor to the 
similar pressure blades upon the right. As these sections 
are equal and symmetrical they counterbalance each other, 
so that no further dummies are required than the small 
one already referred to. 

For regulating the steam supply in accordance with the 
load, two methods other than that of simple throttling with 
its sacrifice of temperature head are available. 

The- admission area may be varied by the cutting in and 
out of nozzles. 

The duration of the time of admission through a con- 
stant area may be varied. 

The first is the Curtis method, impracticable for a full- 
admission turbine like the Parsons ; the second, that which 
has been developed by the Westinghouse engineers for the 
Parsons as they build it. The adoption of the partial ad- 
mission for first stage in the double flow machine gave the 



608 Steam Engineering 

Westinghouse designers their option of the two methods, 
but they have preferred to continue the variable duration 
puff system^ already described in connection with single 
flow machines. A disadvantage of the variable nozzle 
method of regulation is^ that if the area of the nozzles of 
the succeeding stages is correctly proportioned to pass 
along the steam admitted by a certain number of primary 
nozzles^ it will be too great when fewer nozzles are in 
action^ and too small when there are more. This will 
result in a considerable variation of the pressure in the 
succeeding stages^ and of the pressure ratios of expansion 
and jet velocity acquired in those stages^ and interfero 
with the designer's intention with regard to the distribu- 
tion of work and the relation of blade to jet velocity. This 
could be overcome only by adjusting the nozzles of the suc- 
ceeding individual stages in harmony with those of the 
initial stage. 

If^ on the other hand^ the passages through the turbine 
are permanently arranged in the correct relation to each 
other^ this relation will persist whether the flow is con- 
tinuous or intermittent^ and the energy developed can be 
regulated to the demand by making the flow more nearly 
continuous, as the load approaches the rated capacity of 
the machine. So far as the change in initial pressure due 
to the alternate letting on and shutting off of the steam is 
concerned, theory indicates, and experiment proves that 
where the expansion in each stage is but a small part of 
the total range, as in the Parsons turbine, the initial and 
terminal pressures of each stage rise and fall, resulting in 
a fairly constant pressure ratio at each successive expan- 
sion; in other words, for small ranges, and throttle gov- 
erning, the nozzle and blade areas are reasonably correct 



Westinghouse-Parsons Steam Turbine 609 

through a wide range of load and pressure distribution. 
For this reason the impulse section of the Westinghouse 
turbine^ doings say, only one-fifth of the total work, is 
properly proportioned for a wide range in load and may be 
governed without resorting to intermediate nozzle control, 
and without sacrifice of economy and fractional loads. 

Advantage Gained, — The balancing pistons have been re- 
duced to a minimum. In the single-flow t3^pes the high- 
pressure dummy occupies fully one-half of the total dummy 
piston length on the shaft, while the low-pressure piston 
is 2^/2 times the high-pressure diameter. 

A reduction of nearly 50 per cent in shaft span between 
bearings. Owing to the rotor construction a better loading 
of the shaft is also obtained; that is, the rotor weight is 
transmitted to the shaft at points nearer the bearings than 
in the single-flow rotor, where the weight is largely dis- 
tributed. 

An increase to about double rotative speed made possible 
by the reduction in shaft span and loading; that is, to a 
general greater rigidity of the double-flow construction. 

A reduction of about 70 per cent in the bulk of the main 
parts of the machine with practically the same output. 

Internal cylinder stresses due to high-pressure and high- 
temperature steam are avoided by isolating the incoming 
steam within separate nozzle chambers, so that the main 
body of the turbine is subjected to steam having not much 
over '75 pounds gauge pressure with practically no super- 
heat. 

The bulk of the low-pressure stage is better distributed 
and the length of the low-pressure blades greatly reduced 
by subdividing this stage into two parts located at opposite 
ends of the rotor. 

As will be plain from what has preceded, the advantages 



610 



Steam Engineering 



sought in this form of turbine are constructional and me- 
chanical rather than economic. For high-pressure work 
the standard Westinghouse-Parsons single-flow turbine will 
be built up to capacities of 3^000 kilowatts; above 5,000 
kilowatts all units will be built upon the double-flow prin- 




FiG. 253 

3,000 K. W. WESTINGHOUSE DOUBLE FLOW STEAM TURBINE 

ciple. The latter construction will also be used for the 
low-pressure turbines to which it is so admirably adapted, 
as shown in Fig. 252, which is a section of the Westing- 
house low-pressure, double-flow, steam turbine designed 
for utilizing the exhaust steam from non-condensing recip- 
rocating engines. Fig. 253 shows a view of a double-flow 
steam turbine without the generator attached. 



The Curtis Steam Turbine 

In the Curtis turbine the heat energy in the steam is 
imparted to the wheel^ both by impulse and reaction^ but 
the method of admission differs from that of the Westing- 
house-Parsons^ in that the steam is admitted through ex- 
panding nozzles in which nearly all of the expansive force 
of the steam is transformed into the force of velocity. The 
steam is caused to pass through one^ two, or more stages 
of moving elements, each stage having its own set of ex- 
panding nozzles, each succeeding set of nozzles being greater 
in number and of larger area than the preceding set. The 
ratio of expansion within these nozzles depends upon the 
number of stages, as, for instance, in a two-stage machine, 
the steam enters the initial set of nozzles at boiler pres- 
sure, say 180 lbs. It leaves these nozzles and enters the 
first set of moving blades at a pressure of about 15 lbs., 
from which it further expands to atmospheric pressure in 
passing through the wheels and intermediates. Trom the 
pressure in the first stage the steam again expands through 
the larger area of the second stage nozzle to a pressure 
slightly greater than the condenser vacuum at the entrance 
to the second set of moving blades, against which it noWv 
impinges, and passes through still doing work, due to 
velocity and mass. 

From this stage the steam passes to the condenser. If 
the turbine is a four-stage machine and the initial pressure 
is 180 lbs., the pressure at the different stages would be dis- 
tributed in about the following manner : Initial pressure, 
180 lbs.; first stage, 50 lbs.; second stage, 5 lbs.; third 

611 



612 



Steam Engineering 



stage^ partial vacuum, and fourth stage, condenser vacuum. 

Pig. 254 gives a general view of a 5,000 K. W. turbine 

and generator. The generator is shown at the top, while 

the turbine occupies the middle and lower section. A por- 




FiG. 254 

5,000 K. W. CURTIS STEAM TURBINE DIRECT CONNECTED TO 5.000 K. W. 
THREE-PHASE ALTERNATING CURRENT GENERATOR 

tion of the inlet steam pipe is shown, ending in one nozzle 
group at the side. There are three groups of initial noz- 
zles, two of which are not shown. The revolving parts of 
this unit are set upon a vertical shaft, the diameter of the 



Curtis Steam Turbine 613 

shaft corresponding to the size of the unit. For a machine 
having the capacity of the one illustrated by Fig. 254 the 
diameter of the shaft is 14 in. 

The shaft is supported by, and runs upon a step bearing 
at the bottom. This step bearing consists of two cylindrical 
cast iron plates, bearing upon each other and having a 
central recess between them into which lubricating oil is 
forced under pressure by a steam or electrically driven 
pump, the oil passing up from beneath. A weighted ac- 
cumulator is sometimes installed in connection with the 
oil pipe as a convenient device for governing the step bear- 
ing pumps, and also as a safety device in case the pumps 
should fail, but it is seldom required for the latter pur- 
pose, as the step bearing pumps have proven, after a long 
service in a number of cases, to be reliable. The vertical 
shaft is also held in place and kept steady by three sleeve 
bearings, one just above the step, one between the turbine 
and generator, and the other near the top. These guide 
bearings are lubricated by a standard gravity feed system. 
It is apparent that the amount of friction in the machine 
is very small, and as there is no end thrust caused by the 
action of the steam, the relation between the revolving and 
stationary blades may be maintained accurately. As a con- 
sequence, therefore, the clearances are reduced to the mini- 
mum. 

The Curtis turbine is divided into two or more stages, 
and each stage has one, two or more sets of revolving 
blades bolted upon the peripheries of wheels keyed to the 
shaft. There are also the corresponding sets of stationary 
blades, bolted to the inner walls of the cylinder or casing. 
As in the Westinghouse-Parsons type, the function of the 
stationary blades is to give direction to the flow of steam. 



614 Steam Engineering 

Fig. 255 illustrates one stage of a 500 K. W. turbine in 
course of construction. It will be observed that there are 
three wheels^ and that in the spaces between these wheels 
the stationary buckets or vanes are placed^ being firmly 
bolted to the casing. Fig. 256 shows sections of both 
revolving and stationary buckets ready to be placed in 




Fig. 255 
500 k. w. curtis steam tukbine in course of construction 

position. The illustration in Fig. 255 shows the lower or 
last stage. The clearance between the revolving and sta- 
tionary blades is from 3^ to iV ii^v thus reducing the 
wasteage of steam to a very low percentage. The diameters 
of the wheels vary according to the size of the turbine., 
that of a 5,000 K. W. machine being 13 ft. 



iOurtis Steam Turbine 



615 




REVOLVING BUCKETS FOR CURTIS STEAM TURBINE 




stationary buckets for curtis steam turbine 
Fig. 256 




Fig. 257 

NOZZLE 



Fig. 257 shows a nozzle diaphragm with its various 
openings^ and it will be noted that the nozzles are set at 
an angle to the plane of revolution of the wheel. 



616 



Steam Engine erihg 



Fig. 258 is a diagram of the nozzles, moving blades andi 
stationar}^ blades of a two-stage Curtis steam turbine. Thfc 
steam enters the nozzle openings at the top, controlled by 



•.St^o-rr? ^/"iest. 



"i 



M^^^^^S 










♦ 



A/fo v^/'jrt^ J9 /<=rc/G.s 



A/OZ Z fG JD/hrJo/->fcr^ 




AfoUTTf^ jB/dC/G^ 






A7ov/^/r»^ /3/CK3^GS 



J3/Gtc/G.S 



iA'tov^^r>gr/9/<aro^G 3 



CQXCCCOXCCCCCCCCCCCC 






1 I I 1 1 



Fig. 258 

DIAGRAM OF NOZZLES AND BUCKETS IN CURTIS STEAM TURBINE 

the valves shown, the regulation of which will be explained 
later on. In the cut Fig. 258 two of the valves are open, 
and the course of the steam through the first stage is indi- 



Curtis Steam Turbine 617 

cated by the arrows. After passing successively through 
the different sets of moving blades and stationary blades 
in the first stage^ the steam passes into the second steam 
chest. The flow of steam from this chamber to the second 
stage of buckets is also controlled by valves^ but the func- 
tion of these valves is not in the line of speed regulation, 
but for the purpose of limiting the pressure in the stage 
chambers, in a manner somewhat similar to the control of 
the receiver pressure in a two-cylinder or three-cylinder 
compound reciprocating engine. 

The valves controlling the admission of steam to the 
second, and later stages differ from those in the first group 
in that they partake more of the nature of slide valves and 
may be operated either by hand, or automatically; in fact, 
they require but very little regulation, as the governing 
is always done by the live steam admission valves. 

Action of the Steam in a Two-stage Machine, — As prev- 
iously stated, the steam first strikes the moving blades in 
the first stage of a two-stage machine at a pressure of about 
15 lbs. above atmospheric pressure, but with great velocity. 
From this wheel it passes to the set of stationary blades 
between it and the next lower wheel. These stationary 
blades change the direction of flow of the steam and cause 
it to impinge the buckets of the second wheel at the proper 
angle. 

This cycle is repeated until the steam passes from the 
first stage into the receiving chamber, or steam chest for the 
second stage. Its passage from this chamber into the 
second stage is controlled by valves, which, as before stated, 
are regulated either by hand, or automatically. The course 
of the steam through the nozzles and blades of the second 
stage is clearly indicated by the arrows, and it will be 
noted that steam is passing through all the nozzles. 



618 Steam Engineering 

At this point it might be well to consider the question 
which no doubt arises in the mind of the student in his 
efforts to grasp the underlying principles in the action of 
the steam turbine. Why is it that the impingement of the 
steam^ at so low a pressure^ against the blades or buckets 
of the turbine^ imparts such a large amount of energy 
to the shaft? 

The answer is^ because of velocity^ and a good example 
of the manner in which velocity may be made to increase 
the capacity of an agent to do work is illustrated in the 
following way: Suppose that a man is standing within 
arm^s length of a heavy plate glass window and that he 
holds in his hand an iron ball weighing 10 lbs. Suppose 
the man should place the ball against the glass and press 
the same there with all the energy he is capable of exerting. 
He would make very little, if any, impression upon the 
glass. But suppose that he should walk away from the 
window a distance of 20 ft. and then exert the same amount 
of energy in throwing the ball against the glass, a different 
result would ensue. The velocity with which the ball would 
impinge the surface of the glass would no doubt ruin the 
window. Now, notwithstanding the fact that weight, energy 
and time involved were exactly the same in both instances, 
yet a much larger amount of work was performed in the 
latter case, owing to the added force imparted to the ball 
by the velocity with which it impinged against the glass. 

Speed Regulation. — The governing of speed is accom- 
plished in the first set of nozzles, and the control of the 
admission valves here is effected by means of a centrifugal 
governor attached to the top end of the shaft. This gover- 
nor, by a very slight movement, imparts motion to levers, 
which in turn work the valve mechanism. The admission 



Curtis Steam Turbine 



619 



of steam to the nozzles is controlled by piston valves, which 
are actuated by steam from small pilot valves which are in 
turn under the control of the governor Fig. 259 shows the 




"1 



Fig. 259 
governor for 5,000 k. w. turbine 

form a governor for a 5,000 K. W. turbine, and Fig. 260 
shows the electrically operated admission valves for one 
set of nozzles. 



620 Steam Engineering 

Speed regulation is affected by varying the number of 
nozzles in flow, that is for light loads fewer nozzles are open^ 
and a smaller volume of steam is admitted to the turbine 
wheel, but the steam that is admitted impinges the moving 
blades with the same velocity always, no matter whether 
the volume be large or small. With a full load and all the 
nozzle sections in flow, the steam passes to the wheel in a 
broad belt and steady flow. 




Fig. 260 
electrically operated valve 

In addition to the method just described, of actuating 
the addmission valves by steam, the General Electric Com- 
pany, manufactures of the Curtis Turbine, have recently 
introduced a system of hydraulicaly operated valves for 
speed regulation. 

These valves are also of the poppet type, and each is 
closed by a helical spring in compression. In the closed 
position they are held tight by steam pressure, against 
which they are opened. The valves on one machine are all 



Curtis Steam Turiine 



621 



duplicates^ and are opened in rotation by cams (one for 
each valve) mounted on a shafts each cam being given in 
succession an angular advance over its predecessor. This 




Fig. 261 
I cam shaft is rotated by the piston in a hydraulic cylinder, 
the cylinder being mounted either on the generator or 
valve casing. 



622 Steam Engineering 

The valves open gradually; that is there will be throt- 
tling on the opening, or closing valve, before the next one 
in either side is opened or closed, so that the exact amount 
of steam required can be admitted for any definite load. 
Fig. 261 shows a section of the hydraulic cylinder, and 
controlling valve. The position of piston A is controlled 
by a balanced piston valve B. The liquid under pressure 
is admitted at C, and discharged at D. The rod E is con- 
nected with the governor, and rod F with the piston rod. 

Operation. — The rod E receives its motion from the 
governor, and occupies a fixed position for any given speed 
between the limits through which the governor is designed 
to operate. The lever arms G and G^ and H and H' are 
so proportioned that the piston A will occupy a definite 
fixed position to correspond with any position of rod E. 

Therefore as the crosshead K transmits its motion 
through connecting rod N; (see Fig. 262) to the crank 
L on the cam shaft M, there will be a fixed number of 
valves open for any position of the governor. While the 
turbine is operating at a fixed speed, the piston valve will 
occupy a central position, closing both ports and P. 
When there is a drop in speed, the governor causes rod E 
to move down, thus opening part to discharge, and port 
P to admit liquid under piston A which them moves up- ' 
wards, opening more valves. to satisfy the demand for steam. 
In moving up the piston transmits its motion through rod 
F to the piston valve B, restoring it to the central position. 
When operating on a fixed, or slightly varying load, the 
main piston should not continuously move over a distance 
greater than that corresponding to the lap of the piston 
valve, and under no condition of * governing should the 
main piston continually travel back and forth over a dis- 



Curtis Steam Turbine 



b23 




Fig. 262 



tance greater than this. Any larger movements should 
only occur when greater or less power is demanded for 



624 Steam Engineering 

considerable variation in load. Any continuous opening 
and closing of the valves during a steady load is an indi- , 
cation of excessive friction in the governor riggings, or pis- 
ton valve, and it should be eliminated as soon as possible. 

It is essential that the pistons on the piston valve B, 
Pig. 261 be reduced in diameter at their centers gV in. 
as indicated in the illustration. If this is not done it may 
be responsible for sticking of the piston valve, thereby in- 
terfering with the satisfactory regulation of the machine. 

For different machines the connections may be altered, 
and in some the operation is reversed, by crossing the ports, 
so that the piston A will move in the same direction as the 
piston valve B, and in the application of the gear to later 
machines of large capacity, it has been found advisable to 
place the cylinder horizontal, operating crank shafts of 
valve casings by means of rack and pinion with bevel gear 
transmission, or with racks operating directly on pinions 
on cam shafts, but the principle of operation is the same, 
only modified in application to suit particular cases. 

Adjustment. — With the piston A, and the piston valve 
B, both in their mid positions, the rod P should be of such 
a length that the lever Gr will be horizontal. The connect- 
ing rod N is adjusted so that with piston A at the extreme 
end of its up stroke, all the steam valves are open, and the 
first one just ready to close. With the piston A in this 
position (i. e., at the extreme end of its stroke,) and the 
governor at the low speed position, the rod E should be 
adjusted so that the piston valve B, will be in its mid 
position. 

Precautions. — (1) It is absolutely essential that all con- 
nections between governor and valve be entirely free from 
friction. 



Curtis Steam Turbine 625 

(2) The piston valve B must move freely for the whole 
length of its stroke, so that if the rod E be disconnected 
from the arm G, the valve will drop of its own weight, 
either with pressure on or off. 

(3) There must be absolutely nb binding at any of the 
joints through the whole travel. 

(4) The liquid used must be entirely free from dirt;, or 
grit, of any nature. 

(5) On the main steam valves; in the closed position, 
when the roller has ridden off of the cam, it must not press 
on the cam shaft, as this will prevent valve seating properly. 

(6) The piston valve and bore must be perfectly round 
and absolutely straight, or an excessive leakage will be 
established on one side of the valve, causing it to bind. 

(7) The pressure exerted by the main valve springs in 
the open position must be in excess of that sufficient to 
overcome steam pressure on rod, and any friction that may 
exist in packing. 

(8) The plate below main valve springs must be a slid- 
ing fit in guides at all temperatures. 

(9) Care must be taken in the adjustment of the length 
of the rods E and F, that in no position of the governor, or 
piston, can the piston valve become jammed at the end of 
its stroke. 

(10) A heavy oil must not be used or the action will be 
sluggish. 

Piping. — Pig. 263 shows a diagram of piping for a ma- 
chine using oil to operate the valves. This is supplied by the 
same pumps that furnish lubrication for the guide bearings. 
A relief valve K, is adjusted to the desired pressure for 
operating the gear. When the speed is constant and the 
valve not taking any oil, the excess supplied by pumps will 
be discharged through this relief valve. 



626 



Steam Engineering 



The special reducing valve shown in Fig. 264, and at S, 
Fig. 263, is provided to control the amount of oil supplied 
to the bearings. 

This valve can be closed, or adjusted over a wide range, by 
altering the effective length of baffler. 

Eeferring to Fig. 263, the tank marked ^^air chamber^^ is 






Oi/ranfr 




Suction 
Fig. 3 

Fig. 263 



7^o Oro/'n ^/r C/tomOer 
^ffe//ef Va/ve 



provided in order to give a reserved capacity of oil should 
the pumps for any reason stop, and also to form an air 
cushion on the system. The valve at the top of this tank 
should be kept closed, and the oil allowed to compress the 
air contained in the tank, and from time to time the tank 
should be completely emptied and refilled with air. The 



Curtis Steam Turbine 



627 



emptying can be easily accomplished by opening the three- 
way valve to discharge to the oil tank. This need not in- 
terfere with the operation of the machine. After the air 
chamber is emptied^ valve J should be closed;, and the three- 
way valve open to admit oil to the chamber. 



QU 




Fig. 264 



In installations where oil is used for the turbine step 
bearing;, oil for the operating gear and bearings may be 
taken from the high pressure pipe line, on the pump side 
of the step baffler, through a reducing valve. The piping 



628 



Steam Engineering 



system remains as shown diagramatically in Fig. 263 except 
for change in source of snpply of operating flnid. 

In case the station installation includes an air compres- 




FiG. 265 

sor, this equalizing tank may be piped in the system, the 
connection being made on the side of the tank (as provided 
for). The refilling of the tank is thus much simplified, 
and its capacity for emergency operation greatly iEcreasen 



Curtis Steam Turbine <S2£ 

Care should be taken to insure tightness of both valve con- 
trolling air supply to tank^, and pet cock at the top. 

Step Bearing. — Fig. 265 is a section through the cast iron 
step blocks. The lower block in the illustration has two 
holes drilled in it to match the two dowel pins seen project- 
ing from the other block. There is another hole through 
the center of the lower block threaded for %" pipe — The 
step lubricant (oil or water) is forced up through this hole^, 
and out between the raised edges in a film^ thus floating the 
rotating elements of the turbine on a frictionless disk of 
lubricant. The upper side of the top step block is counter- 
bored to fit the lower end of the turbine shafts in which 
there is also a slot for the reception of a key that is fitted 
across the top end of the step block. 

The counterbore centers the block, the dowel-pins guide 
the key into the slot, and the key causes the block to turn 
with the shaft. These are all close fits, and when it be- 
comes necessary to remove the block for inspection or re- 
pairs, it must be pulled off by means of a screw introduced 
into a threaded hole in the under side of the lower block. 
The whole is supported by, and rests upon a large screw that 
passes up through a block of cast-iron which has a threaded 
bronze bushing that forms the nut for the screw. The 
large block termed the cover plate is held to the base of the 
turbine by eight 11/4 inch cap screws. A good idea of the 
construction may be gained by reference to Fig. 266 which 
is a section of the lower portions. It will be noticed that the 
% in. oil supply pipe passes up through the entire length 
of the large step supporting screw, and connects with the 
oil passage through the lower step block. 

Clearance. — With the Curtis turbine, the matter of clear- 
ance is very important. There must be no rubbing contact 



630 



Steam Engineering 



between the revolving and stationary buckets. IsTeither 
must there be too much clearance. Provision is therefore 
made for inspection^ and adjustment of the clearance in the 
following manner. A two inch hole is drilled and tapped 




OU'Brain 



Fig. 266 



into each stage^ sometimes opposite a row of moving blades 
and sometimes opposite the stationary blades. 

Two inch plugs are screwed into these holes, to be re- 
moved when an inspection is to be made. The clearance is 



Curtis Steam Turbine 631 

^not uniform in all the stages^ but is least in the first stage, 
^and greatest in the last. The clearances in each stage of a 
d500 K W machine for instance are as follows: 1st stage 
10.06 to 0.08, 2nd stage 0.08 to 0.1, 3d stage 0.08 to 0.1, 
4th stage 0.08 to 0.2. 

These clearances are measured by clearance gages, which 
are tapering slips of steel about ^/^-in. wide accurately 
ground and graduated by markings, the difference in thick- 
ness of the gage between graduations being 0.001-in., the 
graduations being 1/2-in- apart. 

When it is desired to measure the clearance, one of the 
2 inch plugs is taken out, and a clearance gage which has 
previously been rubbed with red lead is inserted between 
the revolving and stationary buckets as far as it will go, v 
and then pulled out. 

The red lead marking on the gage will show how far it 
went in, and the nearest graduation in thousandths of an 
inch will show the clearance, after noting which, the red 
lead is rubbed on the gage again, and it is tried on the 
other side, and if there is any difference either high or low 
it is corrected by placing the wheel as nearly in the middle 
of the clearance space as possible, which is done by means 
of the step supporting screw shown in Pig. 266. 

The clearance may be adjusted while the machine is run- 
ning at full speed in the following manner: turn the step 
supporting screw until the wheels are heard or felt to rub 
slightly, then mark the screw, and turn it in the opposite 
direction until the wheels rub again. After marking the 
screw at this point, it should be turned back half way be- 
tween the two marks. 

This method of adjusting the clearance requires great 
skill, and experience, and it would seem that the gage 
method is to be preferred for safety. 



632 Steam Engineering 

Packing. — The shaft of the Cnrtis turbine is packed with 
carbon packings where it passes through the top head of the 
wheel case. This packing consists of blocks of carbon made 
into rings^ each ring consisting of three segments which 
break joints. These rings are fitted to the shaft with a 
slight clearance^ and soon get a smooth polish which is not 
only frictionless but steam tight. The rings are held close 
to the shaft either by light springs^ or the pressure of the 
steam in the case. 

The Baffler, — This is a device for restricting the flow of 
water, or oil to the step and guide bearing. Its most im- 
portant function is to steady the flow from the pump, and 
maintain a constant oil film as the pressure varies with the 
•load, and in cases where several machines are operating on 
the same step-bearing system, the baSier fixes the flow tO' 
each machine. The amount, and pressure of oil or water 
required to float a turbine, and lubricate the guide bearing 
depend upon each other, and also upon the condition of the 
step bearing. Usually from 4l^ to 5^/2 gallons per min- 
ute flowing under a pressure of from 425 to 450 lbs. per sq. 
in. is found to be correct for a 1500 K W machine; of 
course larger machines require a heavier pressure. The area 
of the step bearing must be considered also. The principle 
upon which the baffler operates is as follows : into the barrel 
or body of the device is iijserted a plug which is simply a 
square threaded worm, the length of which, and the dis- 
tance it enters the barrel of the baffler determining the 
amount of flow. The more turns that the water must pass, 
the less will be the flow. 



The De Laval SteamTurbine 

The De Laval steam turbine^ the invention of Carl 
De Laval of Sweden^ is noted for the simplicity of its con- 
struction and the high speed of the wheel — 10^000 to 30^000 
E. P. M. The difficulties attending such high velocities 
are^ however^ overcome by the long^, flexible shaft and the 
ball and socket type of bearings^, which allow of a slight 
flexure of the shaft in order that the wheel may revolve 
about its center of gravity^ rather than the geometrical 
center or center of position. All high speed parts of the 
machine are made of forged nickel steel of great tensile 
strength. But one of the most striking features of this 
turbine is the diverging nozzle^, also the invention of De 
Laval. 

It is well known that in a correctly designed nozzle the 
adiabatic expansion of the steam from maximum to mini- 
mum pressure will convert the entire static energy of the 
steam into kinetic. Theoretically this is what occurs in 
the De Laval nozzle. The expanding steam acquires great 
velocity, and, the energy of the jet of steam issuing from 
the nozzle, is equal to the amount of energy that would be 
developed if an equal volume of steam were allowed to 
adiabatically expand behind the piston of a reciprocating 
engine, a condition, however, which for obvious reasons 
has never yet been attained in practice with the reciprocat- 
ing engine. But with the divergent nozzle the conditions 
are different. 

Eef erring to Fig. 267, a continuous volume of steam 
at maximum pressure is entering the nozzle at E, and, pass- 

633 



634 



Steam Engineering 



ing through it, expands to minimum pressure at F, the 
temperature of the nozzle being at the same time constant, 
and equal to the temperature of the passing steam. The 




Fig. 267 
de laval nozzle 



principles of the De Laval expanding nozzle are in fact 
more or less prominent in all steam turbines. The facilities 
for converting heat into work are increased by its use, and 



De Laval Steam Turbine 



635 



the losses by radiation and cooling influences are greatly 
lessened. 

The De Laval steam turbine is termed by its builders 
a high-speed rotary steam engine. It has but a single 
wheels fitted with vanes or buckets of such curvature as 



I 




Fig. 268 
the de laval turbine wheel and nozzles 

has been found to be best adapted for receiving the im- 
pulse of the steam jet. There are no stationary or guide 
blades, the angular position of the nozzles giving direction 
to the jet. Fig. 268 shows the form of wheel and the 
nozzles. The nozzles are placed at an angle of 20° to the 



636 Steam Engineering 

plane of motion of the buckets^ and the course of the 
steam is shown by the illustration. 

The heat energy in the steam is practically devoted to 
the production of velocity in the expanding or divergent 
nozzle^ and the velocity thus attained by the issuing jet 
of steam is about 4^000 ft. per second. To attain the 
maximum of efficiency the buckets attached to the peri- 
phery of the wheel against which this jet impinges should 
have a speed of about 1^900 ft. per second^ but^ owing to 
the difficulty of producing a material for the wheel strong 
enough to withstand the strains induced by such a high 
speed;, it has been found necessary to. limit the peripheral 
speed to 1^200 or 1^300 ft. per second. 

Fig. 269 shows a De Laval steam turbine motor of 300 
H. P.^ which is the largest size built up to the present 
time^ its use having been confined chiefly to light work. 

The turbine illustrated in Fig. 269 is shown directly 
connected to a 200 " K. W. two-phase alternator. The 
steam and exhaust connections are plainly shown^ as also 
the nozzle valves projecting from the turbine casing. The 
speed of the turbine wheel and shaft is entirely too high 
for most practical purposes^ and it is reduced by a pair of 
very perfectly cut spiral gears^ usually made 10 to 1. 
These gear wheels are made of solid cast steely or of cast 
iron with steel rims pressed on. The teeth in two rows 
are set at an angle of 90° to each other. This arrange- 
ment insures smooth running and at the same time checks 
any tendency of the fehaft towards end thrust, thus dis- 
pensing with a thrust bearing. 

The working parts of the machine are clearly illustrated 
in Fig. 270, and a fairly good conception of the assembling 



De Laval Steam Turbine 



637 




Fig. 269 



of the various members, and especially the reducing gears, 
may be had by reference to Pig. 271, which shows a 110 



€3b 



Steam Engineering 




Fig. 270 



B. P. turbine and rotary pnmp with the upper half of the 
gear case and field frame removed for, purposes of inspec- 



De Laval Steam Turbine 



639' 




Fio. 271 

tion. The slender shaft is seen projecting from the center 
of the turbine case, and upon this shaft are shown the 



640 Steam Engineering 

small pinions meshing into the large spiral gears upon the 

two pump shafts. 

Eef erring to Fig. 270^ A is the turbine shaft, B is the 
turbine wheel, and C is the pinion. As the turbine wheel 
is by far the most important element, it will be taken up 
first. It is made of forged nickel steel, and it is claimed 
by the builders, the De Laval Steam Turbine Co., of Tren- 
ton, Xew Jersey, that it will withstand more than double 
the normal speed before showing any signs of distress. A 
clear idea of the construction of the wheel and buckets 
may be had by reference to Pig. 268. The number of 
buckets varies according to the capacity of the machine. 
There are about 350 buckets on a 300 H. P. wheel. The 
buckets are drop forged, and made with a bulb shank 
fitted in slots milled in the rim of the wheel. 

Pig. 272 is a sectional plan of a 30 H. P. turbine con- 
nected to a single dynamo, and Pig. 273 is a sectional ele- 
vation of the same. 

The steam, after passing the governor valve C, Pig 273, 
enters the steam chamber D, Pig. ^72, from whence, it is 
distributed to the various nozzles. The number of these 
nozzles depends upon the size of the machine, ranging 
from one to fifteen. They are generally fitted with shut- 
off valves (see Pig. 269) by which one or more nozzles can 
be cut out when the load is light. This renders it possible 
to use steam at boiler pressure, no matter how small the 
volume required for the load. This is a matter of great 
importance, especially where the load varies considerably, 
as, for instance, there are plants in which during certain 
hours of the day a 300 H. P. machine may be taxed to its 
utmost capacity and during certain other hours the load 
on the same machine may drop to 50 H. P. In such cases 




Fig. 272 



642 Steam Engineering 

the number of nozzles in action may be reduced by closing 
the shut-off valves until the required volume of steam is 
admitted to the wheel. This adds to the economy of the 
machine. After passing through the nozzles, the steam, 
as elsewhere explained, is now completely expanded, and 
in impinging on the buckets its kinetic energy is trans- 
fefred to the turbine wheel. Leaving • the buckets, the 
steam now passes into the exhaust chamber G, Fig. 272, 
and out through the exhaust opening H, Fig. 273, to the 
condenser or atmosphere as the case may be. 

The gear is mounted and enclosed in the gear case I, 
Fig. 272. J is the pinion made solid with the flexible 
shaft and engaging the gear wheel K. This latter is 
forced upon the shaft L, which, with couplings M, connects 
to the dynamo, or is extended for other transmission. 

0, Fig. 273, is the governor held with a taper shank in 
the end of the shaft L, and by means of the bell crank P 
operates the governor valve C. The flexible shaft is sup- 
ported in three bearings, Fig. 272. Q and E are the pin- 
ion bearings and S is the main shaft bearing which carries 
the greater part of the weight of the wheel. This bearing 
is self-aligning, being held to its seat by the spring and cap 
shown. 

T, Fig. 272, is the flexible bearing, being entirely free to 
oscillate with the shaft. Its only purpose is to prevent 
the escape of steam when running non-condensing, or the 
admission of air to the wheel case when running condens- 
ing. The flexible shaft is m^ade very slender, as will be 
observed by comparing its size with that of the rotary pump 
shaft in Fig. 271. It is by means of this slender, flexible 
shaft that the dangerous feature of the enormously high 
speed of this turbine is eliminated. 



De Laval titeam Turbine 



643 




Fig. 273 



644 



Steam Engineering 



The governor is of the centrifugal type, although dif- 
fering greatly in detail from the ordinary fly ball governor, 
as will be seen by reference to Fig. 274. It is connected 
directly to the end of the gear wheel shaft. Two weights 
B are pivoted on knife edges A with hardened pins C, 
bearing on the spring seat D. E is the governor body** 
fitted in the end of the gear wheel shaft K and has seats 




Fig. 274 



milled for the knife edges A. It is afterwards reduced in 
diameter to pass inside of the weights and its outer *end is 
threaded to receive the adjusting nut I, by means of which 
the tension of the spring, and through this the speed of the 
turbine, is adjusted. When the speed accelerates, the 
weights, affected by centrifugal force, tend to spread apart, 
and pressing on the spring seat at D push the governor 



De Laval Steam Turbine 645 

pin G to the right, thus actuating, the bell crank L and cut- 
ting off a part of the flow of steam. 

It has been found necessary with this turbine, when 
running condensing, to introduce a valve termed a vacuum 
valve, also controlled by the governor, as it has been found 
that the governor valve alone is unable to hold the speed 
of the machine within the desired limit. The function of 
the vacuum valve is as follows: The governor pin G act- 
uates the plunger H, which is screwed into the bell crank 
L, but without moving the plunger relative to said crank. 
This is on account of the spring M being stiffer than the 
spring N, whose function is to keep the governor valve open 
and the plunger H in contact with the governor pin. When 
a large portion of the load is suddenly thrown off, the 
governor opens, pushing the bell crank in the direction of 
the vacuum valve T. This closes the governor valve, which 
is entirely shut off* when the bell crank is pushed so far that 
the screw barely touches the vacuum valve stem J. 
Should this not check the speed sufficiently, the plunger 
H is pushed forward in the now stationary bell crank, and 
the vacuum valve is opened, thus allowing the air to rush 
into the space P in which the turbine wheel revolves, and 
the speed is immediately checked. 

The main shaft and dynamo bearings are ring oiling. 
The high-speed bearings on the turbine shaft are fed by 
gravity from an oil reservoir, and the drip oil is collected 
in the base and may be filtered and used over again. 

The fact that the steam is used in but a single stage or 
set of buckets and then allowed to pass into the exhaust 
chamber might appear at first thought to be a great loss 
of kinetic energy, but, as has been previously stated, the 
static energy in the steam as it enters the nozzles is con- 



646 



Steam Engineering 



verted into kinetic energy by its passage through the diver- 
gent nozzles^ and the result is a greatly increased volume of 
steam leaving the nozzles at a tremendous velocity, but at 
a greatly reduced pressure — practically exhaust pressure — 
impinging against the buckets of the turbine wheel and 
thus causing it to revolve. 




Fig. 275 



Efficiency tests of the De Laval turbine show a high econ- 
omy in steam consumption^ as for instance^ a test made by 
Messrs. Dean and Main of Boston^ Mass.^ on a 300 H. P. 
turbine, using saturated steam at about 200 lbs. pressure 
per sq. in. and developing 333 Brake H. P., showed a steam 
consumption of 15.17 lbs. per B. H. P., and the same ma- 
chine, when supplied with superheated steam and carrying 



De Laval Steam Turbine 647 

a load of 352 B. H. P., r-onsiimed but 13.94 lbs. per B. 
H. P. These results compare most favorably with those of 
the highest type of reciprocating engines. 
. Fig. 275 shows a cross section of a 300 H. P. De Laval 
wheel;, showing the design necessary for withstanding the* 
high centrifugal stress to which these wheels are subjected. 
All De Laval wheels are tested to withstand the centrifugal 
stress of twice their normal velocity without showing signs 
of fatigue. 

A characteristic feature of the De Laval steam turbine i^ 
that none of its running parts are subject to the full press- 
ure of the steam^ as the steam is fully expanded in the nozzle 
before it reaches the turbine wheel. This feature^, which 
will not be found in any other heat motor^, is of great value 
and promising future in the direction of using high press- 
ures with resultant increase in economy of fuel. The restric- 
tion as to the steam pressure that can be used is found only 
with the boiler^, and as far as the steam turbine itself is con- 
cerned^ it, has been operated successfully with a pressure as 
high as 3^,000 lbs. per square inch. 



AUis-Chalmers Steam Turbine 

Fig. 276 shows a general view of the AUis- Chalmers 
steam tnrbine^ and although it is essentially of the ^^Par- 
sons^^ type^ still there are a number of modifications in 
details of construction^ as compared with the Westinghouse- 
Pars(ms. steam turbine^ some of which^ no doubt may be 
considered as adding to the efficiency^ and durability of 
the machine. 

Pig. 277 is a sectional view of the ^^elementar}^^^ Parsons 
type of steam turbine, and its various parts are described 
as follows: 

Main bearings, A and B. Thrust bearing, E. Steam 
pipe C. Main throttle valve, D, which is balanced, and 
operated by the governor. Steam enters the cylinder 
through passage E, passes to the left through the alternate 
rows of stationary and revolving blades, leaving the cylinder 
at P and passes into the condenser, or atmosphere through 
passage G. H, J and K are the three steps or stages of the 
machine. L, M and IST are the three balance pistons. 0, P 
and Q are the equalizing passages, connecting the balance 
pistons with the corresponding stages. 

Pig. 278 shows a sectional veiw of the ^Tarsons^^ turbine 
with the AUis-Chalmers modifications. L and M are the 
two balance pistons at the high pressure end. Z is a smaller 
balance piston placed in the low pressure end, yet having 
the same eflEective area as did the larger piston N shown in 
Fig. 277. and Q are the two equalizing passages for 
pistons L and M. Passage P is omitted in this construc- 
tion, and balance piston Z is equalized with the third stage 

649 




Fig. 276 
the allis-chalmers steam turbine 



Allis-Chalmers Steam Turbine 



651 



pressure at Y. Valve Y is a by-pass valve to allow of live 
steam being admitted to the second stage of the cylinder 
in case of a sudden overload. This by-pass valve is the 
equivalent of the by-pass valve used to admit live steam to 




CLEHENTARY Rl^RS0N8 TYPE STEAM TURBINE 

Fig. 277 



the low pressure cylinder of a compound reciprocating en- 
gine. Valve V is arranged to be operated^ either by the 
governor or by hand^ as the conditions may require. Fric- 




Fias 

OEMENTARY mRSONS TVJRBME WITH AUl&CHALIffRS HOOmCATIQNB 



Fig. 278 



tionless glands made tight by water packing are provided 
at S and T where the shaft passes out of the cylinder. The 
shaft is extended at U and connected to the generator shaft 
by a flexible coupling. 



652 Steam Engineering . 

The action of the steam, and the general arrangement of 

the stationary, and moving blades is practically the same 

in the two turbines, with the exception that, in the larger 

sizes of the AUis-Chalmers turbine the ^^balance^^ pistons for 



rrprrr 




MOVING 
BLADES 



STATrONARY 
BLADES 



MOVING 
BLADESf 



STATIONARY 
BLADES 



rrrmr 



MOVING 
BLADES 



STATIONARY 
BLADES 



Fig. 279 

Showing Arrangement of Blading and Course of the Steam in 
Parsons Steam Turbine 

neutralizing the end thrust, are arranged in a different 
manner, the largest one of the three pistons (piston N — 
Fig. 277) is replaced by a smaller balance piston. 

This piston presents the same effective area for the steam 
to act upon, as did the larger piston, for the reason that the 



Allis-Chalmers Steam Turbine 653 

working area of the latter in its original location consisted 
only of the annular area included between its periphery 
and the periphery of the next smaller piston. The 
pressure of the steam is brought to bear upon this 
equalizing piston in its new position^ by means of passages 
or ports through the body of the rotor, connecting the third 
stage of the cylinder with the supplementary cylinder^ in 
which the piston revolves. Fig. 279 shows the arrangement 
of bladings the course of the steam being indicated by the 
arrows. The clearances between the edges of the revolving 
and stationary blades^ as shown in the cut are relatively 
Out of proportion to the actual clearances allowed. 

This clearance is preserved by means of a small thrust- 
bearing provided inside the housing of the main bearing. 

This thrust-bearing can be adjusted to locate and hold 
the rotor in such a position as will allow sufficient clear- 
ance to prevent actual contact between the moving and 
stationary blades^ and yet reduce the leakage of steam to 
a minimum. 

The method by which the blades are fitted to and held 
in the rotor and cylinder of the Allis-Chalmers steam tur- 
bine is as follows: Each blade is individually formed by 
special machine tools^ so that its root or foot is of an an- 
gular, or dove-tail shape, and at its tip there is a projection. 
In order that the roots of the blade may be firmly held in 
position, a foundation ring, A, Fig. 280, is provided, which 
after being formed to a circle of the proper diameter, has 
slots cut in it by a special milling machine. 

These slots are formed of dove-tail shape to receive the 
roots of the blades, and are at the same time accurately 
spaced, and inclined so as to give the required pitch and 
angles to the blades. 



654 



Steam Engineering 



The foundation rings are also of dove-taii snape in cross- 
section^ those holding the stationary blades are inserted 
in dove-tail grooves in the cylinder and those holding the 
revolving blades being pressed into the rotor or spindle. 

The rings are firmly held in their places by key-pieces 
driven into place and upset into under-cut grooves, thus 
positively locking the whole structure together, and making 




Fig. 280 

it practically impossible for a blade' to get out of place. 

The tips of the blades are held and firmly bound together 
by a shroud-ring, B, Fig. 280. 

The shroud-rings are made channel-shape, in cross-sec- 
tion, the flanges being made thin in order to prevent 
dangerous heating in case of accidental contact with either 
the walls of the cylinder or the surface of the rotor. 



AUiS'Chalmers Steam Turbine 655 

The bearings of this turbine are of the self-adjusting 
ball and socket type^ designed for high speed. Sh,inis are 
provided for proper alignment. The lubrication of the 
four bearings^ two for the turbine, and two for the gen- 
erator, is accomplished by supplying an abundance of oil 
to the middle of each bearing and allowing it to flow out 
at the ends where it is caught, passed through a cooler^ 
and pumped back to the bearings. 

The fact that the oil is supplied in large quantities to 
the bearings does not involve a heavy oil bill. 

The journals are practically floating on films of oil, thus 
preventing that ^Vearing out^^ of the oil that occurs when 
it is supplied in small "doses.^^ 

The governor is driven from the turbine shaft by means 
of cut gears working in an oil-bath. 

The governor operates a balance throttle valve b}^ means 
of a relay, except in very small sizes in which the valve 
is worked direct. 

In order to provide for any possible accidental derange- 
ment of the main governing mechanism, an entirely sep- 
arate safety, or over-speed governor is furnished.' This 
governor is driven directly by the turbine shaft without 
the intervention of gearing, and is so arranged and adjusted 
that if the turbine should reach a predetermined speed above 
that for which the main governor is set, the safety governor 
will come into action and trip a valve, shutting off the 
steam and stopping the turbine. A strainer is provided 
through which the steam is passed before admission to 
the turbine. 

For connecting the rotors of the turbine and generator 
a special type of flexible coupling is used to provide for any 
slight inequality in the wear of the bearings, to permit 



656 Steam Engineering 

axial adjustment of the turbine spindle^ and to allow for 
differences in expansion. This coupling is so made that it 
can be readily disconnected for the removal of the turbine 
spindle, or of the revolving field of the generator. Provi- 
sion is made for ample lubrication of the adjoining faces 
of the coupling. The coupling is enclosed in the bearing 
housing, so that it is completely protected against damage^ 
and cannot cause injury to the attendants. 

Waste of heat by radiation is prevented in the following 
manner : 

The hot parts of the turbine, up to the exhaust chamber 
are covered with an ample thickness of non-conducting 
material and lagged with planished steel. 

For large AUis- Chalmers turbines the bedplate is di- 
vided into two parts, one carrying the low-pressure end 
of the turbine and the bearings of the generator, the other 
carrying the high-pressure end of the turbine. The tur- 
bine is secured to the former, while the latter is provided 
with guides which permit the machine to slide back and 
forth with differences of expansion caused by varying tem- 
perature, at the same time maintaining the alignment. 

Fig. 281 shows the spindle, or rotor of the Allis- Chalmers 
turbine. The rings which carry the blades are pressed on 
the shaft. Fig. 282 illustrates the blades as they appear 
when fitted on to the rotor. The shroud ring protecting 
the tips of the blades is also shown in place. Fig. 283 
shows another view of the blade construction. This is a 
half-ring of blades inserted in the foundation ring before 
being placed upon the rotor. 

Fig. 284 shows several rows of stationary blades as they 
appear, fitted in the cylinder of an Allis- Chalmers steam 
turbine. 



Allis-Chalmers Steam Turbine 657 




Fig. 281 

ROTOR OF ALLIS-CHALMERS STEAM TURBINE 



steam Engineering 




Fig. 282 
Starting Up. — As a rule in preparing to start a steam 
turbine, especially one of the "Parsons/^ type, the first 



AUis-Chalmers Steam Turbine 609 

move is to open the throttle slightly^, to allow as much steam 
as possible to flow through the turbine without causing it 
to start. This requires but a few seconds, and about an 
equal period of time is required to start the auxiliary oil 
pump. The inlet valve is always left open to the surface 
condensers, so they are always full of water. The outlet valve 
is quickly opened a certain number of turns, which is known 
to be sufficient for all purposes, and this is easily done be- 
fore the moderate amount of steam flowing through has had 
time to heat the condenser unduly. By this time the oil 
is sufficiently high in the reservoir to permit the turbine to 
be started very slowly, and it doubtless warms up rather 
more evenly when turning over than when standing. When 
the oil has reached its normal level in the reservoir, the 
turbine is given more steam, and the field cut in. 

The principal precautions to be observed are, not to start 
without properly warming up, also to be certain that the oil 
is circulating freely through the bearings. 

The vacuum should not be on until the water glands seal, 
and care should be taken not to run on vacuum without a 
load on the turbine. 

If a turbine vibrates objectionably when started after a 
moderate time has been allowed for warming, say 6 minutes 
for a 500-kilowatt, 10 minutes for a 2000-kilowatt, and 15 
or,perhaps 20 minutes for larger sizes, it is highly probable 
that there is something structurally wrong with it, and any 
longer period will do but little, if any, good; furthermore, 
it will be subject to mysterious ^"^spells^^ or "fits^^ of vibra- 
tion upon changes of load or vacuum. 

In Operation. — The throttle, and inlet gages should be 
closely watched, to see that neither the pressure, nor the 
steam temperature varies much. The vacuum should also 



660 



Steam Engineering 




Fig. 283 



Allis-Chalmers Steam Turbine 661 

be kept constant, as well as the water glands, and those 
pressures indicated by the oil gages. The temperature of 
the oil flowing to and from the bearings should not exceed 
135° Fahr.— . 



Fig. 284 

Shows a Number of Rows of Stationary Blades Fitted in the 

Cylinder of an Allis-Chalmers Steam Turbine 

The governor parts also should be oiled at regluar 
intervals. 

Stopping the turbine is practically the reverse of start- 
ing, the successive steps being as follows : starting the aux- 



662 Steam Engineering 

iliary oil pump, freeing it of water and allowing it to run 
slowly ; removing the load gradually ; breaking the vacuum 
when the load is almost zero, shutting off ,the condenser 
injection and taking care that the steam exhausts freely 
into the atmosphere ; shutting off the gland water Avhen the 
load and vacuum are off; pulling the automatic stop to 
trip the valve and shut off steam and, as the speed of the 
turbine decreases, speeding up the auxiliary oil pump to 
maintain pressure on the bearings ; then, when the turbine 
has stopped, shutting down the auxiliary oil pump, turning 
off the cooling water, opening the steam chest drains and 
slightly oiling the oil inlet valve-stem. During these 
operations the chief particulars to be heeded are: not to 
shut off the steam before starting the auxiliary oil pump 
nor before the vacuum is broken, and not to shut off the 
gland water with vacuum on the turbine. The automatic 
stop should also remain unhooked until the turbine is about 
to be started up again. 

General Suggestions, — Water used in the glands of the 
turbine must be free from scale-forming impurities, and 
should be delivered at the turbine under a steady pressure 
of not less than 15 pounds. The pressure in the glands 
will vary from 4 to 10 pounds. This water may be warm. 
In the use of water for the cooling coils and of oil for the 
lubricating system, nothing more is required than ordinary, 
good sense dictates. An absolutely pure mineral oil must 
be supplied, of a nonfoaming charcter, and it should be 
kept free through filtering from any impurities. 

These suggestions apply more particularly to steam tur- 
bines of the ^Tarsons^^ type, exhausting into condensers. 
For turbines built to be run non-condensing the portion 
relating to vacuum does not of course apply. 



Hamilton-Holzwarth Steam Turbine 

In order to thoroughly understand the underlying prin- 
ciples of the steam turbine^ and the action of the steam 
within it^ one must get definitely fixed in his mind this 
fact^ viz./ that there is no similarity between it and the 
reciprocating engine, and the action of the steam upon the 
piston in driving it back and forth. In fact, there is more 
similarity between the reciprocating engine and the rotary 
engine than there is in the case of the turbine. In the 
rotary engine the steam pushes a piston in the same manner 
as it does in the reciprocating engine, with the exception 
that the piston of the rotary engine travels entirely around 
the shaft, while the piston of the reciprocating engine 
travels back and forth in a straight line motion. It will 
be much easier to get a clear idea of the action of the tur- 
bine if one will for the time being drop all knowledge he 
may have of reciprocating and rotary engines. He will 
then be able to more readily grasp, and better understand 
the action of the steam turbine. 

One of the most comprehensive, and at the time most 
simple explanations of the action of the steam upon the 
blades of the turbine, and also upon the piston of the 
reciprocating engine, in both of which cases rotary motion 
is produced, but in two different ways, is given by Hans 
Holzwarth. He says : "Take a large wheel which is 
fastened to a vertical shaft. Grasp this wheel at the rim 
at a certain point, and walk continuously around the shaft, 
always retaining the hold, like a horse walking around 
a capstan fastened to a bar or pole which he pulls after him. 

663 



664 Steam Engineering 

Or stand still in a certain spot and take the wheel by the 
rim and cause it to revolve (like opening and closing a 
valve by hand)^ by changing hands so that the whole rim 
is constantly revolving/^ 

The first illustration clearly explains the manner in 
which the shaft of the reciprocating engine is caused to 
revolve^ by means of the static expansion force of the steam 
acting upon the crank pin^ through the medium of 
the piston, piston rod, cross head, and connecting 
rod. In the second illustration, in which the man 
turns the wheel by simply standing still in one place, and 
causing the wheel to revolve by grasping the rim and giv- 
ing it a push, first with one hand, and then with the other^ 
we have a simple explanation of how the steam causes the 
shaft of the turbine to revolve, by a constant series of 
pushes, or impulses against the movable blades that are key 
seated to the drum, which in turn is keyed to the shaft, 
the moving blades representing the rim of our wheel. 

Every one knows that in order to be able to turn the 
aforesaid wheel the man must have a good floor to stand 
upon, and he must also have a good foothold on the floor, 
because he exerts the same amount of pressure on the 
floor, that he exerts against the rim of the wheel. This 
explains why there must be stationary blades, as well as 
revolving blades in a turbine. 

The actual pressure exerted upon any single blade in a 
turbine is in reality very light. Take, for example, a 300 
K. W. Westinghouse turbine. There are altogether in a 
machine of this size 31,073 blades, of which 16,095 are mov- 
ing blades. The pressure that each blade exerts in turning 
the shaft is a little over one ounce, but owing to the large 
number of blades, and the velocity of the steam, the power 
is developed. 



Hamilton-IloJzwartli Steam Turbine 665 




Fig. 285 

HAMILTON-HOLZWARTH STEAM TURBINE 



The Hamilton-Holzwarth steam turbine resembles in 
many respects the Westinghouse-Parsons turbine, prominent 



•"66 Steam Engineering 

of which is that it is a full stroke turbine ; that is^ the steam 
flows through it in one continnous belt^ or veil in a screw 
line^ the general direction being parallel with the shaft. 
But nnlike the Parsons type^ the steam in the Hamilton- 
Holzwarth turbine is made to do its work only by impulse, 
and not by impulse and reaction combined. The smaller 
sizes are built in a single casing or cylinder, but for units 
of 750 K. W. and larger there are two parts, viz., high 
and low pressure, thus resmbling in some respects a com- 
pound reciprocating engine. 

The Hamilton-Holzwarth steam turbine is based upon 
and has been developed from the designs of Prof. Bateau, 
of Paris, and is being manufactured in this country by 
the Hooven-Owens-Eentschler Co., of Hamilton, Ohio. It 
is horizontal, and placed upon a rigid bed plate of the box 
pattern. All steam, oil and water pipes are within and 
beneath this bed plate, as are also the steam inlet valve and 
the regulating and by-pass valves. 

There are no balancing pistons in this machine, the 
axial thrust of the shaft being taken up by a thrust ball- 
bearing. The interior of the cylinder is divided into a 
series of stages by stationary discs which are set in grooves 
in the cylinder, and are bored in the center to allow the 
shaft, or rather the hubs of the running wheels that are 
keyed to the shaft, to revolve in this bore. 

Clearance, — The clearance allowed is as small as prac- 
ticable, as it is in this clearance between the revolving hub 
and the circumference of the bore of the stationary disc 
that the leakage losses occur. It should be noted that be- 
tween each two stationary discs there is located a running 
wheel, and that the clearance between the running vanes 
and the stationary vanes is made as slight as is consistent 



w 



Hamilton-Holzwarth Steam Turbine 667 



with safe practice; otherwise leakage would occur here 
also, and besides this there would be a distortion of the 
steam jet and entrainment of the surrounding atmosphere, 
resulting in a rapid decline in economy if the clearance 
between the stationary and moving elements was not re- 
duced to as small a fraction as possible. 

As before stated, the stationary discs are firmly secured 
to the interior walls of the casing. At intervals on the 
outside periphery of these discs are located the stationary, 
or guide vanes. These are made of drop forged steel. They 
are set in a groove on the outside edge of the disc and 
fastened with rivets. Both disc and vanes are then ground, 
giving the vanes the profil-e that they should have for the 
most efficient expansion of the steam. After this is done 
a steel ring is shrunk on the outside periphery of the vanes 
and the steam channels in the disc. These discs are then 
placed in the grooves in the casing at regular intervals, 
and in the spaces between them are the running wheels. 

The casing is divided into an upper and lower half. The 
running wheels are built with a cast steel hub having a 
steel disc riveted on to each side, thus forming a circum- 
ferential ring space into which the running vanes are 
riveted. A thin steel band or rim is tied on the outer edge 
of the vanes, thus forming an outer wall to the steam 
channels and confining the steam within the vanes. . These 
vanes are also milled on both edges, on the influx, and 
efflux side of the wheel, thus forming them to the shape 
corresponding to the theoretical diagram. 

In all steam turbines one of the main requisites for a 
quiet-running machine is that the revolving element or 
rotor shall be perfectly balanced. The rotary body of the 
Hamilton-Holzwarth turbine consists of a plurality of run- 



668 Steam Engineering 

ning wheels, each one of which is balanced by itself before 
being placed upon the shaft. All the bearings are lubri- 
cated in a thorough manner by oil forced up into the bot- 
tom bushing or shell under slight pressure. Flexible coup- 
lings are used between the high and low-pressure shafts, 
and for connecting the turbine shaft to the generator shaft 
or other shaft to be driven. By means of the thrust ball- 
bearing on the exhaust end of the turbine the shaft may 
be adjusted in an axial direction in such a manner as to 
accurately preserve the desired position of the running 
wheels. 

Fig. 285 shows a general view of the Hamilton-Holz- 
warth turbine, and the action of the steam within the ma- 
chine may be described as follows : After leaving the 
steam separator that is located beneath the bed plate, the 
steam passes through the inlet or throttle valve, the stem 
of which extends up through the floor near the high- 
pressure casing and is protected by a floor stand and 
equipped with a hand wheel, shown in Fig. 285. The 
steam now passes through the regulating valve. From this 
valve it is led through a curved pipe to the front head of 
the high pressure casing or cylinder. In this head is a 
ring channel into which the steam enters, and from which 
it flows through the flrst set of stationary vanes. In these 
vanes the first stage of expansion occurs. 

Construction of the Stationary Blade. — A stationary 
blade is constructed in the following manner: A circular 
cast-iron disc a. Fig. 286, has a bore b corresponding to 
the diameter of the shaft, with the necessary clearance. 
On the outer circumference of this disc there is cut a 
groove c. -The stationary guides, consisting of a vane of 
proper curvature and the adjoining piece, are of drop- 



Hamilton-Hohwarth Steam Turbine 



669 



forged steel;, milled on all sides of the adjoining piece which 
-fits into the circular groove c. These vanes are arranged 
all around tlje circumference so that one adjoining piece 
touches another and they are held in place and fastened 
^securely, by rivets e, to the disk. The outer circumference 
;of these vanes is turned off to the right size, and then a 
steel ring f is shrunk over them. This shrunk ring pro- 
jects into the grooves of the housing. 




Fig. 286 

The Running Wheel. — While in the stationary blade the 
weight is not of great importance, in the running wheel it 
is very essential to reduce the weight as much as possible. 
It will be readily understood that the lighter the running 
wheels are, the less the bearings will have to support, and 
therefore the shorter they may be constructed, and the 
better they will work. Furthermore, by keeping down the 
weight of the running wheel the shaft diameter is kept 
within small limits. This determines the bore of the sta- 
tionary blade, and with that the circular space between the 
bore of the stationary blade and the shaft can be kept 



670 



Steam Engineering 



within small limits; therefore in the construction of this 
running wheel every dead and unnecessary weight is ■ 
avoided. 

The running wheel is made up as follows : A steel hub 
or spider a^ Fig. 287, has a bore b fitting closely to the 
shaft diameter. On both side of the hub are riveted steel 
discs c. The groove on the outer circumference of the 
steel disc is turned out and forms a receptacle for the 
running vanes. The running vane itself consists of the 




Fig. 287 

properly curved blade, with an adjoining piece made in one 
section of drop-forged steel. The adjoining piece is fin- 
ished and fits closely into the grooves of the steel disc. The 
running vanes are held in place and rigidly connected to 
the steel discs by rivets d, so that the centrifugal force of 
each vane is taken up by a rivet and transmitted through 
the rivet to the steel disc. The outer edge f of the vane is 
turned off and thus provided with an annular groove form- 
ing a receptacle for the steel band g, which is tied all 
around the wheel. It is held in place and secured to the 



Hamilton-Holzwarth Steam Turbine 671 

^ vanes by riveting over the projecting ends of the vanes. 
^ The ends of the band are brazed together. 

.Eeference to Fig. 288^ which is a vertical section of this 
'turbine^ will serve to make more clear the action of the 
'steam within the machine. The turbine casing a, is made 
of cast iron of cylindrical shape, and split in the horizontal 
axis, into the upper half, a, and the lower half, b. In the 
horizontal points the two halves are bolted together steam 
tight. The lower half, b, is cast together with the pedestal, 
e, which is the support for the low pressure bearing, d, and 
the groove, e, for the stuffing box, f . The outlet opening, 
g, is arranged in the lower half, b. This lower half is sup- 
ported on pads of the bed plate, h, with two feet extending 
on the sides, and fastened thereto. The front head, i, is 
bolted steam tight to the flange, k, on the front side of 
the casing. In front of the -head, i, is located the regu- 
lating mechanism pedestal, 1, which combines the high 
pressure bearing with the housing for regulating mechan- 
ism, n, and housing, o, for the governor, p. A live steam 
pipe, g^y is connected to an inlet valve, r, and this to a main 
regulating valve, s, to the inlet flange of the front head, 1. 
The passage of the steam into this front or high pressure 
,head has already been referred to. In the grooves cut in 
the housing are the stationary blades, t, and in the space 
between the two following stationary blades is the running 
wheel, u. All running wheels fit on the shaft, v, and are 
'keyed to the shaft. The shaft, v, is supported in the high 
ipressure bearing, m, on one end, and in the low pressure 
bearing, d, on the other end. The low pressure bearing 
has an arrangement which allows the adjustment of the 
shaft, V, lengthwise in the direction of the turbine. On 
the outer end of the shaft is the coupling, w, keyed to the 



e72 



Steam Engineering 




Fig. 288 

hamilton-holzwarth steam turbine 

Sectional Elevation 



Hamilton-Hohwarth Steam Turbine 



673 



shaft. This coupling allows connection to be made to 
the generator^ pnmp^ or blower^ which is to be driven by 
the turbine. 

The flow of the steam from^the inlet valve^ r^ to the 
exhaust outlet^ g^ and the manner of the working of the 
steam in the turbine is as follows : The steam passing 
through the main regulating valve^ s^ enters the circular 
channel of the front head^ i, and from here it flows through 
a circular slot to the first stationary blade^ t. Opposite this 
circular slot is arranged a multitude of vanes^ x^ Fig. 2^9, 





Fig. 289 



which give the steam the right expansion in the right 
direction. With this velocity attained in the stationary 
blades^ the steam impinges upon the vanes^ u, of the first 
running wheel, and the bore of the housing can be kept 
within larger limits, because the steam flowing through 
the vanes is prevented from flowing rapidly outward by 
means of a band secured around the outer circumference 
of the running wheel. 

The running vanes conform in section somewhat to the 
Parsons type, but the action of the steam upon them, and 



674 Steam Engineering 

also within the stationary vanes is different. The expan- 
sion of the steam, and consequent development of velocity 
takes place entirely within the stationary vanes, which also 
change the direction of flow of the steam^ and distribute 
it in the proper manner to the vanes of the running wheels^ 
which, according to the claims of the makers, the steam 
enters and leaves at the same pressure, thus allowing the 
wheel to revolve in a uniform pressure. 

Jn the low-pressure casing, which is larger in diameter 
than the high-pressure, the steam is distributed in the 
same manner as it is in the high-pressure casing. There 
is, however, in the front head of the low-pressure casing 
an additional nozzle through which live steam may be ad- 
mitted in case of overload. The design of this nozzle is 
such that the live steam entering and passing through it, 
and controlled by the governor exerts no back pressure on 
the steam coming from the receiver, but, on the contrary, 
its action is similar to the action of an injector, that is, it 
tends to suck the low-pressure steam through the first set 
of stationary vanes of the low-pressure turbine. 

The first stationary disc of the low-pressure turbine has 
guide vanes all around its circumference, so that the steam 
enters the turbine in a full cylindrical belt, interrupted only 
by the guide vanes. To provide for the increasing volume 
as the steam expands in its course through the turbine, the 
areas of the passages through the distributers and running 
vanes must be progressively enlarged. The gradual in- 
crease in the dimensions of the stationary vanes permits 
the steam to expand within them, thus tending to maintain 
its velocity, while at the same time the vanes guide the 
steam under such a small angle that the force with which 
it impinges the vanes of the next running wheel is as 



Hamilton-HolzwartJi Steam Turbine 675 

effective as possible. The curvature of the vanes is such 
that the steam while passing through them will increase its 
velocity in a ratio corresponding to its action. 

The purpose of the stationary discs is, as has been stated, 
to distribute the steam to the running wheel. They also 
take the back pressure of the steam as it impinges the 
vanes of the running wheels, thus in a sense acting as 
balancing pistons. 

The governor is of the spring and weight type, adapted 
to high speed, and is designed especially for turbine govern- 
ing. It is directly driven by the turbine shaft, revolving 
with the same angular velocity. Its action is as follows: 
Two discs keyed to the shaft drive, by means of rollers, 
two weights sliding along a cross bar placed at right angles 
through the shaft and compressing two springs against 
two nuts on the cross bar. Every movement of the weights, 
caused by increasing or decreasing the angular velocity of 
the turbine shaft, is translated by means of levers to a 
sleeve which actuates the regulating mechanism. These 
levers are balanced so that no back pressure is exerted upon 
the weights. The whole governor is closed in by the discs, 
one on each side, and a steel ring secured by concentric 
recesses to the discs. In order to decrease the friction 
within the governor and regulating mechanism, thrust 
ball-bearings and frictionless roller-bearings are used. 

As previously stated, the regulating valve is located be- 
neath the bed plate. One side of it is connected by a curved 
pipe with the front head of the high-pressure cylinder, and 
the other side is connected with the inlet valve. The regu- 
lating valve is of the double-seated poppet valve type. 
Valves and valve seats are made of tough cast steel, to 
avoid corrosion as much as possible, and the valve body is 
made of cast iron. 



676 Steam Engineering 

Immediately below the regulating valve and forming a 
part of it in one steam chamber is located the by-pass regu- 
lating valve. Thus the use of a second stuffing box for 
the stem of this valve is avoided. The function of this 
valve is to control the volume of the live steam supply that 
flows directly to the by-pass nozzles in the front head of 
the low-pressure casing. This valve is also a double-seated 
poppet valve. 

The main regulating valve is not actuated directly by 
the governor^ but by means' of the regulating mechanism. 
The construction and operation of this regulating mechan- 
ism is as follows: The stem of the regulating valve is 
driven by means of bevel gears by a shaft that is supported 
in frictionless roller-bearings. 

On this shaft there is a friction wheel that the governor 
can slide across the face of a continuously revolving fric- 
tion disc by means of its sleeve and bell crank lever. This 
revolving disc is keyed to a solid shaft which is driven by 
a coupling from a hollow shaft. This hollow shaft is driven 
by the turbine shaft through the medium of a worm gear. 
The solid shaft^, with the continuously revolving friction 
disC;, can be slightly shifted by the governor sleeve so that 
the two friction discs come into contact when the sleeve 
moves^ that is^ when the angular velocity changes. If this 
change is relatively great^ the sleeve will draw the periodi- 
cally revolving friction disc far from the center of the 
always revolving one^ and this disc will quickly drive the 
stem of the regulating valve and the flow of steam will thus 
be regulated. As soon as the angular velocity falls below 
a certain percentage of the normal speed, the driving fric- 
tion disc is drawn back by the governor^ the regulating 
valve remains open and the whole regulating mechanism 
rests or stops^ although the shaft is still running 



Hamilton-Hohwarth Steam Turbine 677 

Should the angnlar velocity of the shaft reach a point 
2.5 per cent higher than normal^ the governor will shut 
down the turbine. If an accident should happen to the 
governor^ due to imperfect material or breaking or weaken- 
ing of the springs^ the result would be a shut-down of the 
turbine. 

In order to change the speed of the turbine while run- 
ning, which might be necessary in order to run the machine 
parallel with another prime mover, a spring balance is 
provided, attached to the bell crank lever of the regulating 
mechanism. The hand wheel of this spring balance is 
outside of the pedestal for regulating mechanism and near 
the floor-stand and hand wheel. With this spring balance 
the speed of the turbine may be changed 5 per cent either 
way from normal. 

All the bearings of the turbine are thoroughly lubricated 
with oil forced under pressure by the oil pump driven by 
means of worm gearing by the turbine itself. After flowing 
through the bearings the oil is passed through a filter, and 
from thence to the oil tank located within the bed plate, 
from whence it is taken by the oil pump. All revolving 
parts are enclosed, and the principal part of the regulating 
mechanism operates in a bath of oil. 

The Stuffing-Box. — An effective means of packing a 
swiftly revolving shaft is a long sleeve surrounding the 
shaft with a very small radial clearance. The reason for 
this will be found in the throttling action of the steam par- 
ticles revolving with the shaft. These steam particles have 
a tendency to fly outwardly and so prevent the steam from 
passing axially through the small clearance between the 
shaft and the sleeve. The reader will readily understand 
that it would not be practical to use such a long sleeve in 



678 



Steam Engineering 



the construction of a steam turbine, as this arrangement 
would considerably increase the length of the free shaft. 
For the reason that the deflection of the shaft depends 
upon the third power of the free length of the shafts it is 
absolutely necessary to restrict this free length as much as 
possible. 




Fig. 290 

In the Hamilton-Holzwarth turbine^ use is made of the 
telescopic idea; that is the entire length of the sleeve is 
split into several parts^ and these single parts are shifted 
together. In Fig. 290 the ring A screwed upon the shaft 
projects axially into a groove of the ring B, and revolves 
within it. The ring B does not move at all, but is held in 
place, and pressed tightly against the turbine casing by 
means of the ring C which presses against the bushing of 



Hamilton-Hohwarth Steam Turbine 679 

the bearing. By screwing the ring C on the ring B, both 
rings are forced axially in opposite directions. Prom the 
casing S the steam seeking to escape^, flows axially to T. 
From there it flows back to U^ and then forward to V^ 
being very much throttled in the process. The ring B has 
an annular groove which must be packed with soft packing. 
Any accumulating water is collected in the chamber W^ in 
the bushing of the bearings from whence it is properly 
drained. The ring E serves only the purpose of tightening 
the threads between rings C and B. 



The Rateau Steam Turbine 

The Eateaii turbine is purely an impulse turbine^ using 
wheels of thin plates pressed into a slightly conical form. 
These are mounted on a common shafts and separated from 
each other by division walls. The first wheels have partial 
peripheral admission^ so that the peripheral velocity may be 
high from the very beginning without using too short 
blades. The guide blades are set into division walls^ and 
the rotating blades are bent from a single piece of bronze^ 
or steel plate^ and are riveted to the double turned rim of 
the wheel-disc. The shaft bearings were originally built 
as part of the cover of the turbine^ but now are made inde- 
pendent. At the low pressure end the shaft is made steam 
tight by means of a simple stuffing box^ into which suffi- 
cient water is allowed to flow to secure steam tightness. 
As the same pressure exists on both sides of each rotating 
wheel, the axial thrust has only the small value due to the 
pressure on the area of the end of the front journal. 

Fig. 291 shows a sectional view of the machine, in which 
it is to be noted that the wheel discs are riveted to their 
hubs. 

Fig. 292 shows a view of the turbine with generator, and 
oil equipment. The construction of the wheels, and division 
walls can easily be seen in Figs. 293, 294 and 295. The 
construction according to the latter figure, with division 
walls made in sections is preferred, because after taking 
away the casing cover, all the interior parts are easily 
accessible. 

681 



682 



Steam Engineering 




Fig. 291 
The most recent Eateau turbine is of the action type, 
that is to say, expansion of the steam is fully carried out in 



Rateau Steam Turbine 



683 




Fig. 292 

the distributor for each group consisting of a distributor 
and one moving wheel. The steam therefore acts by its 



684 



Steam Engineering 



velocity and not by its pressure. These turbines are more- 
over multicellular^ that is to say^ they consist of a certain 
number of elements^ each element comprising one dis- 
tributor and one moving wheel. 

This turbine has been developed by the firm of Sautter- 




FiG. 293 



Hartle^ of Paris, France, from designs by Prof. A. Eateau, 
who is also the inventor of the Eateau steam regenerator, 
through which the exhaust from non-condensing recipro- 
cating engines may be passed to a low-pressure turbine, 
thus resulting in the development of power from steam 
which otherwise would be wasted. A very complete and 



Bateau Steam Turbine 



685 



successful installation of this cliaracter has been in opera- 
tion for some time at the extensive steel works of the Inter- 
national Harvester Company at Chicago^ 111.^ and judging 
from the results of an exhaustive series of tests conducted 
by Mr. P. G. Gaesch^ and published in the June^, 1907, 
issue of "Power/^ the system possesses considerable merit. 
The following description of the installation at the Har- 
vester Company's plants is supplied by courtesy of the 
Western Electric Co., of Chicago. 




Fig. 294 



The Steam Regenerator, or accumulator, consists of a 
cylindrical wrought-steel shell % of an inch in thickness, 
11 feet 6 inches in diameter, and 30 feet long, having a 
central horizontal diaphragm which divides the regenerator 
into two similar compartments. In each compartment 
there are six elliptical tubes or steam-distributing conduits, 
A, Pig. 296, which extend from end to end in pairs, and 
are so placed as to leave spaces, B, between them. (The 



686 



Steam Engineering 



sectional view is from another installation and only shows 
four tnbes.) Baffle plates^, C^ are arranged above the space 
between each pair of tubes. The spaces surrounding the 
conduits^ and^ under certain conditions^ even the conduits 
themselves^ are filled with water to the extent that the top 
of the latter is usually submerged three or four inches. 
The sides of the conduits are perforated with a great many 
%-inch holes to allow of the lateral escape of steam through 




Fig. 295 



the water^ with^ occasionally^ a further escape from the 
bottom openings. A large baffle plate in the upper steam 
<5pace serves for a perfect separation of entrained moisture 
from the steam. The steam enters by the pipe shown at the 
left hand of the side elevation^ passes to the interior of the 
elliptical tubes^ and escapes into the spaces through the 
perforations. The circulation of the water takes place in 
the direction of the arrows; the baffle plates placed above 
each pair of tubes prevent the water from being thrown 



Bateau Steam Turbine 687 

Aiico the steam space. This flow of steam gives an extreme 
degree of steam saturation to the water; and the slight 
back pressure which at first might be expected, owing to the 
head of water above the rows of perforations^, is thereby 
reduced to insignificant proportions. 

When the supply of steam from main engine ceases^ the 
water liberates part of the heat it has absorbed^ and an even 
flow of low-pressure steam is given off^ while the steady 
demand of the turbine reduces the pressure in the accumu- 
lator^ causing the steam still retained in the tubes to escape^ 
maintaining the circulation of the water^ and facilitating 
the liberation of the steam. Experience has shown that the 
whole of the contained water participates in the regenera- 
tive action. The steam is taken from the top of the ac- 
cumulator to the turbine^ and the pressure can be regu- 
lated by the relief valve shown. The water level is main- 
tained constant by a ball float contained in a small tank 
arranged at the back of the regenerator. Generally there is 
a slight overflow at all times^ representing among other 
things the ^^make up^^ f rom the exhaust steam supply. The 
regenerator at this plant has a capacity of 55 tons of water^ 
sufficient by actual test to deliver all the steam for a 50 
per cent overload on the turbine for a period of 430 
seconds. At full load this would correspond to a period 
of 390 seconds. The regenerator or accumulator is fitted 
with the following accessories: Firsts an adjustible relief 
valve^ which regulates the limits of pressure in the accumu- 
lator^ and allows the steam to escape when the turbine is 
stopped^ or working on a light load ; it also prevents back 
pressure in the cylinders of the reciprocating engine. 

This valve may be connected to the condenser so that in 
case the turbine is shut down for a period^ the main engines 
may have the benefit of the vacuum. 



688 



Steam Engineering 




Fig. 296 

plan and elevation of low-pressure turbine installation, 

with transverse and longitudinal sections of 

regenerator 



Second^ a non-return water valve^ necessary with water 
accumulators^ to prevent any possibility of reflux of water 
toward the main engines during periods of stoppage. 



Bateau Steam Turbine 689 

Thirds automatic level regulators^ and gauge glasses^ and 
automatic drains. 

Fourth^ piping beginning at the inlet of the receiving 
drum^ including the steam header and mains from the 
regenerator to the turbine^ the exhaust piping from the 
turbine^ and condenser^ and the piping between the con- 
denser and air pump. 

Fifth, a vertical receiving drum_ 9 feet in diameter^ and 
22 feet long^ with baffle plates^ and separating chambers, 
the function of which is to allow the ready escape of steam 
from the main engines without increase of back pressure 
on the system. The expansions allowed in this drum con- 
duce to a more even flow of steam in the steam regenerator. 

Sixths a 30-inch barometric condenser of the Alberger 
type^ complete with air cooler^ exhaust entrainer^ expan- 
sion joint, and an air pump 8x6x12 inches. 

The exhaust steam from a 42x60 Mcintosh & Hemphill, 
rolling mill engine, passes through the regenerator and into 
a Eateau low-pressure turbine, to the shaft of which is 
connected two direct current generators, each of 250 K. W. 
capacity, at 250 volts, and designed so that they may be 
operated in parallel. The bearings are of the ring oiled 
reservoir type, with water jackets. The plant is designed 
with a view of adding another similar unit, but the evidence 
of the tests shows that a 750 K. W. unit can be operated 
with the steam that is available, without allowance for the 
steam (about 6,000 lbs. per hour) that is available from 
auxilliary machinery. 

Part of these auxiliaries already exhaust into an open 
feed water heater, but the steam regenerator, constituting 
a perfect feed heating device, can more appropriately re- 
ceive all the steam from the auxiliaries, with the advantage 
of some addition to the capacity of the turbine equipment. 



690 



Steam Engineering 



Fig. 297 shows a view of the regenerator and attached 
equipment. 

The leading objects of the tests made by Mr. G-aesch were, 
first to determine the steam consumption of the turbine 




Fig. 297 
rateau regenerator, and attached condenser 

per unit of power, and second, to measure the actual 
amount of steam available for the use of the turbine as 
delivered from the main engine. 



Bateau Steam Turbine 691 

Space prohibits a detailed description of the method of 
conducting thei tests^ and the results derived therefrom. 

The average brake horse power developed by the turbine 
according to the report of one of the tests was 544 with a 
steam consumption per B. H. P. per hour of 37 lbs. The 
average steam pressure at the turbine was 16.6 lbs. absolute. 
The average I. H. P. of the main engine during the same 
test was 820^ with a steam consumption of 61.2 lbs. per 
I. H. P. per hour. The total weight of steam available 
per hour from regenerator to turbine was 56.100 lbs. 

The main engine^ the dimensions of which have already 
been given^ was a reversing rolling mill engine. The stuff- 
ing box used in the Eateau turbine is clearly illustrated in 
Figs. 240 to 243. 



The Reidler-Stumpf Steam Turbine 

This turbine is manufactured in Germany and its essen- 
tial characteristics are the peculiarly formed^ parallel re- 
turn buckets derived from the Pelton water wheel, also the 
rectangular nozzles that allow a homogeneous jet of steam 
to be directed against the wheel. Fig. 298 shows a view 




Fig. 298 

of one of the wheels, and Fig. 299 shows sections of a 
bucket, and nozzle. 

The buckets are worked out of a solid forged wheel with 
a milling cutter, consequently they are very strong, and 
durable. 

693 



694 



Steam Engineering 



The steam jet enters the bucket C from the nozzle B, and 
is deflected through ah angle of 180 degrees, the direction 





Fig. 299 



of its exit being parallel to that of its entrance, as shown 
by the arrows (Pig. 299). 



Reidler-Stumpf Steam Turbine 695 

This type of wheel has but a one-sided discharge — Pig. 
300 shows another type of this turbine^ in which the sta- 





FiG. 300 



tionary buckets D, of the reverse guide are opposed to the 
rotating buckets C of the wheel in such a manner as to 
form a continuous closed cylinder in which the steam in 



696 



Steam Engineering 



its course through the wheel continually whirls or spirals 
around and around. With this type of turbine the steam 
enters the bucket wheel from the nozzle as shown in Fig. 
299, but instead of escaping after it has passed once 
through the bucket, it is caught by the guide or stationary 
bucket and returned to the wheel, this process being re- 
peated again and again until practically all of the energy 
in the steam has been abstracted. 




Fig. 301 
Fig. 301 shows a portion of the rim of this style of 
wheel with its symmetrical double buckets. The steam jet 
is split into two symmetrical parts by the sharp middle par- 
tition. The direction of flow of the two steam streams 
is now reversed, and they are returned to the middle plane 
of the wheel by the reverse blades, and again brought to the 
wheel as a united jet. Nearly the entire periphery has 
primary, or secondary admission, and as a result of this 
the fan work of the idle blades is reduced to a minimum. 



Disposal of the Exhaust Steam of 
Steam Turbines 

As in the case of the reciprocating engine^ the highest 
efficiency in the operation of the steam turbine is obtained 
by allowing the exhaust steam to pass into a condenser^ 
and experience has demonstrated that it is possible to main- 
tain a higher vacuum in the condenser of a turbine than in 
that of a reciprocating engine. This is due^ no doubt^ to 
the fact that in the turbine the steam is expanded down 
to a 'much lower pressure than is possible with the recipro- 
cating engine. 

The condensing apparatus used in connection with steam 
turbines may consist of any one of the modern improved 
systems^ and as no cylinder oil is used within the cylinder 
of the turbine^ the water of condensation may be returned 
to the boilers as feed water. If the condensing water is 
foul or contains matter that would be injurious to the 
boilers^ a surface condenser should be used. If the water 
of condensation is not to be used in the boilers, the jet 
system may be employed. Another type of condenser that 
is being successfully used with steam turbines is the Bulk- 
ley injector condenser. 

Among the steam turbines that were on exhibition at the 
St. Louis exposition in 1904 the Westinghouse-Parsons and 
the General Electric Curtis turbines were each equipped 
with Worthington surface condensers^, fitted with improved 
auxiliary apparatus consisting of dry vacuum pumps^ either 
horizontal of the well-known Worthington type^ or rotative 

697 



698 Steam Engineering 

inotor-driven^ a hot well pump^ and a pump for disposing 
of the condensed steam from the exhaust system. The two 
latter pumps were of the Worthington centrifugal type. 
The Hamilton-Holzwarth turbine was equipped with a 
Smith- Vaile surface condenser^ fitted with a duplex double- 
acting air pump^ a compound condensing circulating pump, 
and a rotative dry vacuum pump^ motor-driven. The 
vacuum maintained was high^, 28 to 28.5 in. 

As an instance of the great gain in economy effected by 
the use of the condenser in connection with the steam tur- 
bine^ a 750 K. W. Westinghouse-Parsons turbine, using 
steam of 150 lbs. pressure not superheated and exhausting 
into a vacuum of 28 in.^ -showed a steam consumption of 
13.77 lbs. per B. H. P. per hour^ while the same machine 
operating non-condensing consumed 28.26 lbs. of steam per 
B. H. P. hour. Practically the same percentage in economy 
effected by condensing the exhaust applies to the other 
types of steam turbines. 

With reference to the relative cost of operating the sev- 
eral auxiliaries necessary to a complete condensing outfit, 
the highest authorities on the subject place the power con- 
sumption of these auxiliaries at from 2 to 7 per cent of the 
total turbine output of power. A portion of this is re- 
gained by the use of an open heater for the feed water^ 
into which the exhaust steam from the auxiliaries may 
pass^ thus heating the feed water and returning a part of 
the heat to the boilers. 

A prime requisite to the maintenance of high vacuum^ 
with the resultant economy in the operation of the con- 
densing apparatus^ is that all entrained air must be ex- 
cluded from the condenser. There are various ways in 
which it is possible for air to find its way into the con- 



to 



Disposal of Exhaust Steam 699 

densing system. For instance, there may be an improperly 
packed gland, or there may be slight leaks in the piping, or 
the air may be introduced with the condensing water. This 
air should be removed before it reaches the condenser, and 
it may be accomplished by means of the '^^dry^^ air pump. 

This dry air pump is different from the ordinary air 
pump that is used in connection with most condensing 
systems. The dry air pump handles no water, the cylinder 
being lubricated with oil in the same manner as the steam 
cylinder. The clearances also are made as small as possi- 
ble. These pumps are built either in one or two stages. 

A barometric or a jet condenser may be used, or a surface 
condenser. The latter type lessens the danger of entrained 
air, besides rendering it possible to return the condensed 
steam, which is pure distilled water, to the boilers along 
with the feed water, a thing very much to be desired in 
localities where the water used for feeding the boilers is 
impregnated with carbonate of lime, or other scale-form- 
ing ingredients. 

In comparing the efficiency of the reciprocating engine 
and the steam turbine it is not to be inferred that recipro- 
cating engines would not give better results at high vacuum 
than they do at the usual rate of 25 to 26 in., but to reach 
and maintain the higher vacuum of 28 to 28.5 in. with the 
reciprocating engine would necessitate much larger sizes 
of the low-pressure cylinder, as also the valves and exhaust 
pipes, in order to handle the greatly increased volume of 
steam at the low pressure demanded by high vacuum. 

The steam turbine expands its working steam to within 
1 in. of the vacuum existing in the condenser, that is, if 
there is a vacuum of 28 in. in the condenser there will be 
27 in. of vacuum in the exhaust end of the turbine cylinder. 



700 Steam Engineering 

On the other hand^ there is usually a difference of 4 or 5 
in (2 to 2.5 lbs.) between the mean back pressure in the 
cylinder of a reciprocating condensing engine^ and the 
absolute back pressure in the condenser. 

It therefore appears that the gain in economy per inch 
increase of vacuum above 25 in. is much larger with the 
turbine than it is with the reciprocating engine. Mr. J. E. 
Bibbins estimates this gain to be as follows : between 25 and 
28 in. there is a gain of 3i/4 to 4 per cent per inch of in- 
crease^ and at 28 in. 5 per cent. These results have been 
obtained by means of exhaustive tests conducted by Mr. 
Bibbins. Other high authorities on the steam turbine all 
agree as to the great advantages to be derived by incurring 
the extra expense of erecting a condensing plant that is 
capable of maintaining the high vacuum necessary to high 
eflBciency. 

Another method by which the steam consumption of the 
turbine may be materially decreased^ and a great gain in 
economy effected is by superheating the steam. The amount 
of superheat usually specified is 100°;, and the apparatus 
employed for producing it may be easily mounted in the 
path of the waste gases. The steam may thus be super- 
heated without extra cost in fuel^ and an increase of 8 to 
10 per cent in economy effected. The independent super- 
heater requires extra fuel and labor, and the gain in this 
case is doubtful, but there can be no question as to the wis- 
dom of utilizing the waste flue gases for superheating the 
steam. 

As previously stated, the steam turbine is peculiarly 
adapted for the use of highly superheated steam, and high 
vacuum, and in these two particulars it excels the recipro- 
cating engine. At the present time many large plants are 



Disposal of Exhaust 701 

equipped with turbine engines that are giving the best of 
results^, and the outlook for the future employment of this 
type of power producer is certainly very promising. 

Surface Condensers. — The demand for efficient service in 
the production of power by both the reciprocating engine^ 
and the steam turbine has resulted in bringing to bear upon 
the design of the surface condenser^ some of the thought, 
study and experiment which have heretofore been expended 
upon the other factors of the power plant. Up to within 
the past few years the surface condenser consisted princi- 
pally of an indiscriminate collection of tubes within a metal 
box, with a flood of water following what happened to be the 
path of least resistance, with tubes subjected upon the steam 
side to a shower of water of condensation, keeping the steam 
from contact, and with pockets and quiet corners for steam 
and air and water, with an air-pump large enough for what- 
ever happened, and little attention paid to the getting of 
the air into it, the surface condenser has satisfied the mod- 
erate demands of the past, and awaited the demands created 
by the turbine, and the strenuous central station man for 
scientific treatment along rational lines. 

In a condenser taking care of 200,000 pounds of steam 
per hour, over 55 pounds of water are made upon the tubes 
per second. If this has to drip down over the bank below 
the point at which it is formed, it can readily be seen that 
the lower tubes are going to be busy cooling of! feed-water 
instead of condensing steam, and that the greater rate of 
condensation will occur upon the upper tubes. By arrang- 
ing the tubes in banks, the condensation from each of which 
is quickly drawn to the side and disposed of, by leading 
the steam to a positive and rapid fiow among these tubes 
in a direction counter to the flow of the water, so that the 



702 Steam Engineering 

final contact of the condensed steam and air is with the 
coolest water^, and by subdividing the flow so that the circu- 
lating water travels positively and rapidly past every square 
foot of the cooling surface^ the condenser is made to con- 
dense eighten or twenty instead of six pounds of steam per 
hour per square foot of surface. The significance of this, 
not only in first cost and space occupied, but m mainte- 
nance charges where, as in some of the large stations upon 
the Atlantic seaboard, tubes have to be renewed once in 
about three years, is easy to appreciate, and it is not the tube 
which is condensing lots of steam, but rather that which is 
loafing in an air pocket or an eddy, that is the most likely 
to corrode. 

ITotwithstanding the liability to corrosion of the tubes 
of surface condensers, many of the large engine plants, and 
practically all steam turbine plants have been equipped 
with surface condensers. This is due largely to the saving 
effected by returning the pure water of condensation to 
the boilers. But unless the condenser tubes are closely 
watched for signs of corrosion, there is danger of having 
in the course of time a mixture of cylinder oil and con- 
denser leakage along with the water of condensation, which 
would be a very undesirable boiler feed. This applies to 
reciprocating engine plants. On the other hand a surface 
condenser in connection with a steam turbine is a better 
investment. The turbine water of condensation contains 
no lubricating oil and condenser leakage is the only source 
of trouble to be feared. To maintain this condenser leak- 
age at the lowest practicable minimum is extremely im- 
portant, as this will seriously affect (if the hot-well water 
is used for boiler feed) the percentage of corrosive and 
scale-forming elements fed into the boilers. Even under 



Disposal of Exhaust 703 

normal surface-condenser operation there is a small leakage, 
through the packing at the ends of the tubes, and to this 
is added leakage due to corrosion.. 

The danger of corrosion attacking the tubes of surface 
condensers is much greater in localities upon, or near the 
sea coast where the condensing water is largely impreg- 
nated with salt. 

QUESTIONS AND ANSWERS. 

446. Explain the chief points of difference between 
the action of the reciprocating steam engine, and the steam 
turbine. 

Ans. The piston of the reciprocating engine is driven 
back and forth by the static expansive force of the steam; 
while in the steam turbine, not only is this static expansive 
force made to do work, but the velocity of the steam in ex- 
panding from a high, to a low pressure is also utilized in 
turning the rotor of the turbine. 

447. What other important factors enter into the opera- 
tion of a steam turbine? 

Ans, The principles of reaction and impulse. 

448. Name several of the more important advantages 
that the turbine has over the reciprocating engine. 

Ans. First, highly superheated steam of a high initial 
pressure may be used in the turbine. Second, a larger 
proportion of the heat in the steam may be converted into 
work with the turbine. Third, there is much less friction 
with the turbine. 

449. What is the most economical method of disposing 
of the exhaust steam from a turbine? 

Ans. By allowing it to pass into a condenser. 



704 Steam Engineering 

450. Will the turbine expand the steam to as low a 
pressure as the reciprocating engine will? 

Ans. Yes^ and even lower. 

451. What type of condensing apparatus is necessary 
with the steam turbine. 

Ans, The same kind that is used on reciprocating en- 
gines. 

452. How low will a well regulated turbine allow the 
steam to expand ? 

Ans. To within one inch of the vacuum existing in 
the condenser. 

453. What is the theoretical velocity of steam under 
100 lbs. pressure if allowed to discharge into a vacuum of 
28 inches? 

Ans, 3860 feet per second. 

454. How many ft. lbs. of energy would one cubic ft. 
of steam thus exert? 

Ans, 59,900 ft. lbs. 

455. What is the ratio of bucket speed to jet speed for 
impulse wheels. 

Ans, Bucket speed equals one-half of jet speed. 

456. What should be the ratio between bucket speed 
and jet speed, for reaction wheels. 

Ans, 1 to 1. That is, the two speeds should be equal. 

457. What should be the form or curvature of the 
blades, or buckets? 

Ans. They should be of such form as will permit expan- 
sion of the steam with the least amount of friction, or eddy 
currents. 

458. How are the stuffing boxes of steam turbines usu- 
ally kept cooled? 

Ans, By means of water applied, in various ways. 



Questions and Ansivcr] 705 

459. How is the speed of steam turbines usually regu- 
lated? 

Arts. By simple throttling. 

460. What are the ideal conditions under which a tur- 
bine should work? 

Arts. A full initial pressure^ and all cross sections of 
steam passages to be suitable to the power required. 

461. Of what type is the Westinghouse-Parsons turbine ? 
Ans. It is both an impulse and reaction turbine. 

462. How are the clearances between the blades pre- 
served in this turbine? 

Arts. By means of balancing pistons on the shaft. 

463. What is the usual velocity of the steam in the 
Westinghouse-Parsons turbine ? 

Ans, 600 ft. per second. 

464. How does the efficiency of steam turbines compare 
with that of reciprocating engines? 

Ans, It is generally higher. 

465. How is the heat energy in the steam imparted to 
the wheels of the Curtis turbine ? 

Ans, Both by impulse and reaction. 

466. Describe the method of admission in the Curtis 
turbine. 

Ans, The steam is admitted through expanding nozzles 
in which nearly all of the expansive force of the steam is 
transformed into the force of velocity. The steam is caused 
to pass through one^ two^ or more stages of moving ele- 
ments^ each stage having its own set of expanding nozzles, 
each succeeding set of nozzles being greater in number and 
of larger area than the preceding set. 

467. What is the ratio of expansion in these nozzles? 



706 Steam Engineering 

Ans, The ratio of expansion within these nozzles de- 
pends upon the "nnmber of stages^ as^ for instance, in a two- 
stage machine, the steam enters the initial set of nozzles at 
boiler pressure, say 180 lbs. It leaves these nozzles and 
enters the first set of moving blades at a pressure of about 
15 lbs. 

468. In a four-stage machine, with 180 lbs initial pres- 
sure, what would be the pressures at the different stages ? 

Ans. First stage, 50 lbs. ; second stage, 5 lbs. ; third 
stage, partial vacuum, and fourth stage, condenser vacuum. 

469. How are the revolving parts of the Curtis turbine 
supported ? 

Ans. Upon a vertical shaft, which in turn is supported 
by, and runs upon a step bearing at the bottom. 

470. How is this step bearing lubricated? 

Ans, Oil is forced under pressure by a steam or elec- 
trically driven pump, the oil passing up from beneath. 

471. How is the speed of the Curtis turbine regulated? 
Ans. By varying the number of nozzles in flow. 

472. How are the clearances adjusted in the Curtis 
turbine ? 

Ans. By means of the large step screw at the bottom. 

473. How is the shaft packed to prevent steam leakage? 
Ans. With carbon blocks made into rings fitting the 

shaft. 

474. What type of turbine is the De Laval? 
• Ans. '■■ It is purely an impulse wheel. 

475. What is the speed of the wheel? 

Ans. From 10,000 to 30,000 revolutions per minute. 

476. How is the heat energy in the steam utilized in 
the De Laval turbine? 

Ans. In the production of velocity. 



Questions and Answers 707 

477. What is the velocity of the steam as it issues from 
the expanding nozzles and impinges against the buckets? 

Ans, About 4^000 ft. per second. 

478. What is the nsnal peripheral speed of the wheel? 
Ans. 1^200 to 1^300 feet per second. 

479. Of what type is the Allis-Chalmers steam turbine? 
Ans. It is essentially of the Parsons type. 

480. How are the clearances between the revolving and 
stationary blades preserved? 

Ans. By a thrust bearing. 

481. What kind of bearings has the Allis-Chalmers 
turbine ? 

Ans. Self-adjusting ball and socket bearings. 

482. What is the first move in preparing to start a 
steam turbine? 

Ans. Open the throttle slightly and allow a small vol- 
ume of steam to flow through in order to warm the tur- 
bine. 

483. What should be done next? 
Ans. Start the auxiliary oil pump. 

484. What are the principal precautions to be observed 
when starting a steam turbine? 

Ans. To see that the turbine is properly warmed, also 
to be certain that the oil is circulating freely through the 
bearings. 

485. What type of turbine is the Hamilton-Holzwarth 
steam turbine ? 

Ans. It is an impulse turbine. 

486. Describe in brief its construction? 

Ans. There are no balancing pistons in this machine, 
the axial thrust of the shaft being taken up by a thrust 
ball-bearing. The interior of the cylinder is divided into 



708 Steam Engineering 

a series of stages by stationary discs which are set in 
grooves in the cylinder and are bored in the center to allow 
the shafts or rather the hubs of the running wheels that are 
keyed to the shaft, to revolve in this bore. 

487. In what respect does this turbine resemble a com- 
pound reciprocating engine? 

Arts. The steam is first admitted to the high pressure 
casing, and from there it passes into the low pressure cas- 
ing, which is larger in diameter. 

488. Describe the action of the steam upon the blades? 
Ans. The expansion of the steam takes place entirely 

within the stationary blades, which also change the direc- 
tion of its flow, distributing it to the running vanes. 

489. What additional function do the stationary vanes 
perform ? 

Ans. They take the back pressure, thus acting as balanc- 
ing pistons. 

490. What type of governor has this turbine? 
Ans. The spring and weight type. 

491. How are the bearings lubricated? 

Ans. The oil is forced into the bearings under pressure 
by an oil pump. 

492. Of what type is the Eateau steam turbine? 

Ans. It is an impulse turbine having wheels of thin 
plates, slightly conical. 

493. How is the rotor balanced? 

A71S. The same pressure exists on both sides of each 
rotating wheel. 

494. Does the steam act by velocity or pressure ? 
Ans. By velocity in this case. 

495. What are the essential features of the Eeidler- 
Stumpf steam turbine ? 



Questions and Answers 709 

Ans. The peculiar form of bucket^ and the parallel 
return of the steam. 

496. What is meant by parallel return of the steam? 
Ans. The steam enters the buckets through nozzles, 

and is deflected through an angle of 180 degrees, thus leav- 
ing the rotating buckets in a direction parallel to that of 
its entrance. 

497. Describe the action of the steam within the Eeid- 
ler-Stumpf turbine. 

Ans. Instead of escaping after having once passed 
through the buckets^ it is caught by the guides or stationary 
buckets and returned to the wheel; this process being re- 
peated again^ and again until all of the energy in the steam 
has been made to do work. 

498. How many types of this turbine are there? 

Ans. Two, viz. : The single flow, and the double flow. 

499. How is the highest efficiency obtained in the oper- 
ation of the steam turbine ? 

Ans. By allowing the exhaust steam to pass into a 
condenser. 

600. Is it possible to maintain as high vacuum with 
the turbine as with a reciprocating engine? 

Ans. Experience demonstrates that a higher vacuum 
may be maintained in the condenser of a turbine than is 
possible with reciprocating engines. 

501. What kind of condensing apparatus may be used 
with steam turbines? 

Ans. Any one of the modern improved types. 

502. What is required in order to maintain a high 
vacuum in any type of condenser? 

Ans. That all entrained air be excluded. 

503. How may this be accomplished? 



710 



Steam Engineering 



Ans. By means of a "dry air pump. 

504. In what manner does the dry air pump differ fror 
an ordinary air pump? 

Ans. The dry air pump handles no water, and the clea^ 
ances are made as small as possible.. 

505. To what extent does the steam turbine expand 
working steam? 

Ans, To within one inch of the vacuum existing withij 
the condenser. 

506. Is the steam turbine adapted to the use of supe| 
heated steam? 

Ans. It is. Highly superheated steam may be used, ar 
a high vacuum maintained. 

507. Is the water of condensation from turbines desi| 
able for boiler feed ? 

Ans. It is, for the reason that it contains no lubricatir 
oil, and is a comparatively pure water. 



-^^™^B^M^^^ ^ ^^ ^^^ 



Fio. 302 

ALLIS-CHALMEBS GAS ENGINES AT ILLINOIS STEEL COMPANY'S PLANT, OABT, IND. 



The Gas Engine 



The gas engine differs structurally from the steam engine 
in two particulars, it is much more ponderous than a steam 
engine of equal output and has usually a much heavier 
crank-shaft. The difference in total weight must not be 
laid to the higher mean pressures exerted in the cylinder, 
for, in engines of a certain power, the mean pressure in 
the gas-engine cylinder will be higher than that in the 
steam-engine cylinder, so that for a given power per stroke, 
the gas engine may have the smaller cylinder. But the 
four-stroke -cycle gas engine has only one working stroke 
in four. For a given power, therefore, its cylinder area 
must be four times the area of the steam-engine cylinder, 
per pound of mean effective pressure. Since this latter 
will be as 3 to 2, approximately, the actual cylinder area 
will be as 2.66 to 1, or the diameter ratio will be 1.63 to 1. 

Approximately the gas engine appears fully 50 per cent 
the larger when its piston speed is the same as that of the 
steam engine. This is a very strong inducement to the 
designer to produce an engine which shall do work in both 
ends of the cylinder. Such a design, however, necessitates 
a piston-rod stuffing-box, gland and cooling devices. It 
involves double the number of explosions per minute in 
the cylinder and it renders possible a reduction of the 
cylinder ratio, as compared with a steam engine, to 1.33 
to 1. Regarding single acting, or double acting gas engines, 
the difference in stress on the crank shaft must be taken 
• into account. A single-acting engine produces a torsion in 
the shaft which iw reversed on the next stroke when the 

711 



712 Steam Engineering 

shaft is pushing back the piston. Eeversing stresses are 
about 50 per cent more destructive than stresses in one 
direction only. The crank-shaft strength ratio is thus not 
simply 4:1^ as between a four-stroke and a one-stroke 
method of workings but it is as 6:1^ or diametrally as 
1.8:1;, the strength varying as the cube of the diameter. 
This is why gas-engine crank shafts are so very large and 
this point must be of great importance on the score of cost. 
Indeed the four-stroke engine embodies a large amount of 
material which does very little work during a large pro- 
portion of its working hours. 

The gas engine is a prime mover which derives its power 
or energy from the heat generated by the combustion within 
its cylinder^ of a mixture of gas and air in the proper pro- 
portion to form an explosive. The combustion of this 
charge of gas and air is occasioned under a close or heavy 
compression^ a result of the inward movement of the piston 
after the charge is admitted and all valves closed. The 
result of igniting this mixture imder the heavy compres- 
sion is what is commonly called an explosion^ which is 
nothing more than a quick burning or rapid combustion 
of the mixture. This sudden explosion causes a high degree 
of heat within the cylinder behind the piston, and, the re- 
sultant high initial pressure against the piston drives it 
forward^ and^ through the medium of connecting rod and 
cranky motion is imparted to the main engine shaft. The 
original gas engines^ and a majority of the smaller sizes 
of today^ operate upon the Beau de Eochas cycle or four 
stroke cycle^ sometimes termed the Otto cycle^ meaning that 
an engine completes a cycle in four acts, defined as follows : 
(1) Induction — During an outstroke of the piston, air and 
gas in suitable proportions are drawn into the cylinder. (2) 



The Gas Engine 713 

Compression — The following instroke compresses the com- 
bustible mixture into the clearance space. (3) Explosion 
— ^Ignition of the compressed charge causes a rapid rise of 
pressure and subsequent expansion of products. (4) Ex- 
pulsion^The expanded gases are expelled by the returning 
piston. In this type of gas engine^ two revolutions of the 
crank shaft are necessary in order to complete one cycle. 

Many small engines and some of those of largest power 
are designed upon the 2-stroke cycle^ which is as follows: 
(1) Compression of the charge. (2) Ignition^ explosion 
and expansion^ and at the end of the stroke the exhaust 
products are expelled and the cylinder filled by a mixture 
of gas and air under pressure. In the two cycle engine, 
two compression chambers are necessary^ due to the fact 
that in this type of gas engine consisting of two cylinders, 
either side by side^ or tandem^ the charge of gas and air 
is being received in one cylinder^ while the previous charge 
in the other cylinder is being compressed^ preparatory to 
explosion. A two-cycle engine thus explodes a charge, and 
receives an impulse at each revolution. It is important to 
admit only pure air and gas into engine cylinders. Dust 
and grit^ or tarry matters cause rapid wear of interior sur- 
faces. Care is also necessary to insure the induction of 
cold charges^, in order that maximum density of gas and air 
may be obtained. 

The usefulness of the gas engine as a prime mover is 
greatly enhanced by the fact that suitable power gas may 
now be produced from almost any form of commercial fuel ; 
the cheapness or relative fuel value of the combustible hav- 
ing very little bearing on the value for power purposes of 
the gas produced. ^ For the efficient generation of steam 
the choice of coals is confined within narrow limits ; for gas 



714 Steam Engineering 

production relatively wide limits exist. Thus gas engines 
are operating with practically the same thermal efficiency 
on fuel gases ranging from 1^500 B. T. U. per cubic foot, 
to 90 B. T. TJ. per cubic foot. The former is a rich dis- 
tillate from oil refining, the latter a waste product from 
blast furnaces. The one contains practically no combusti- 
ble, the other as high as 8 per cent. 

Table 37 gives the origin, and some of the properties of 
the usual commercial gases; Table 38 of the usual con- 
stituent gases. 

The power derived from the combustion of these gases 
is, however, far more uniform than at first appears from 
their relative calorific value. For perfect combustion a defi- 
nite amount of air must be mixed with the gas, depend- 
ing upon the amount of combustibles to be neutralized by 
the oxygen in the air. Tor instance Pittsburg natural gas 
requires about 10 to 12 cu. ft. of air per cubic foot of gas, 
while for producer gas about equal volumes of gas and air 
are required. The calorific value of the mixture entering 
the gas engine cylinder thus forms the basis of all calcula- 
tions rather than the heat of the gas itself, and in this 
respect relatively little difference exists between the heat 
value of suitable mixtures, whether the gas be rich or poor. 
For this reason the gas engine is enabled to work efficiently 
with most gases, however lean, provided of course that they 
are properly cleaned or purified from sulphur — ^no dust — 
no tar, etc. 

Combustion. — In gas engine work it is important to 
obtain a speed of combustion neither too rapid nor too 
sluggish. Much then depends upon the relative constitu- 
ents of the gas. Hydrogen burns with the greatest rapidity 
— seven times, faster than methane, and if present in large 



The Gas Engine 715 

quantities, forms an undesirable element with high com- 
pressions, on accou5it of its tendency to premature ignition 
from the heat of compression. On the other hand, the 
comparatively sluggish combustion of methane and other 
heavy hydro-carbons, and the presence of large quantities 
of inert gases such as CO2 and N tends to retard the com- 
bustion of hydrogen, so that a permanent gas, although 
containing a high percentage of hydrogen, if modified by 
a high percentage of more sluggish gases, will prove to be 
a suitable power gas. If, on the other hand, sufficient 
sluggish constituents are not present, compression in the 
engine must be largely reduced. Thus blue water gas (un- 
carburetted) is unsuited to gas engine work on this ac- 
count. Enriched with oil gas ( carburetted ) , water gas be- 
comes somewhat more adaptable; likewise crude oil water 



Coke oven gas may become unsuitable if drawn off for 
too long a period during the coking process?. In most 
forms of modern by-product coke ovens the richer gases are 
drawn off during the first 40 or 50 per cent of the coking 
period (10 hrs. in 24 hr. coke, 16 hrs. in 30 hr. coke) ; 
those gases given off during the latter part being used for 
heating the ovens. During the latter period tne percent- 
ages of methane and hydrogen are rapidly reversed so that 
hydrogen may run as high as 60 or 70 per cent of the total 
volume of gas, which makes it quite unfit for power work. 
The gas delivery must, therefore, be carefully controlled, 
if utilized for power purposes. 

Blast furnace gas, which is simply the product of more 
or less incomplete combustion of carbon in a coke furnace, 
contains less than one-third combustible matter, but forms 
an excedingly satisfactory fuel gas. It is comparatively 



Table 37 
commercial power gases— general properties. 



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The Qas Engine 



111 



Table 38 
constituents of power gases. 



Gas 



Name 



Chemical 
Symbol 



Heating 

Value 



B.T.U. 
Cu. Ft. 

Net 



Rela- 
tive 



Characteristics — Where 
Found 



Hydrogen 



Oxygen 



Nitrogen 



Carbon Monoxide 
or Carbonic Oxide 



Carbon Dioxide 



P Methane or Marsh 
Gas 



H 



N 



CO 



CO2 



CH^ 



' Acetylene 

5 Ethylene OT Ole- 

2 fiant Gas 

Ethane 

Benzene or Benzol 



Carbon 



Sulphur 



CgHg 
C^H, 

CaHe 



278 



326 



913 



1.17 



3.29 



Element formed from decom- 
position of steam (H2O) 
o r hydro - carbon c o m- 
pounds. Burns very rap- 
idly with high flame tem- 
perature. 



Element, not considered a 
combustible as it displaces 
an equal amount of (O) in 
•air for combustion. 



Element. Inert gas entering 
with air (N-79%, 0-21%). 
Retards speed of combus- 
tion. 



Valuable constituent. , Prod- 
uct of incomplete combus- 
tion (oxidation) of C in 
presence of excess carbon. 



Inert gas. Product of com- 
plete combustion of C. 
Occurs in all producer and 
blast gases. Retards speed 
of combustion. 



Most valuable constituent 
evolved by natural or ar- 
tificial decomposition of 
vegetable matter, coal or , 
crude oils. 



1427 51.4 
1490 53.6 



1615 
3955 



58.1 
131.5 



"^ Higher hydro-carbons, usu- 
ally as "illuminants" — 
occur in small quantities 
V in the richer gases, liber- 
I ated during destructive 
I distillation of coal or oil 
— ^Acetylene used alone 
J for lighting. 



C oxidizes to 
plete) and 
plete). CO 
CO2. 



CO (incom- 
CO2 (com- 
oxidizes to 



S oxidizes to SO2 forming 
H2SO4 (sulphuric acid) 
with water. 



718 Steam Engineering 

slow burnings thus permitting compressions as high as 
160-200 lbs. per sq. in. and can be cleansed of dust without 
great difficulty; no tar is, of course, encountered. Owing 
to the fact that nearly 40 per cent less heat is contained 
in a cu. ft. of blast furnace gas mixture than with natural 
gas, larger cylinders are provided on blast furnace gas 
engines for developing the same horse power. The slight 
increase in friction is, however, largely .overcome by in- 
creased thermal efficiency due to higher compression, and 
gas engines designed for this gas give practically the same 
efficiency as those operating on richer gases. 

4 

Induction, — The charge of gas and air in definite propor- 
tions is drawn into the cylinder by the suction of the engine 
piston, and the velocity of entry is in direct proportion to 
the piston speed. The air valve is usually opened before 
the gas valve, but inasmuch as there is no suction created 
until the opening of the air valve, some makers set the 
valves so that the gas valve is approaching its maximum 
lift by the time that the air valve has commenced to open, 
thus ensuring a well mixed charge. Usually, however, the 
settings are arranged so that the first portion of the in- 
duced charge is of air only, then air and gas, and finally 
air with the small quantity of gas swept in by the still 
moving current of air from the passages connecting i:he gas 
and air valve seats. The cams operating the valves are 
carefully designed to permit maximum lift with swift, but 
gradual opening and closing, to accord with the induced 
velocity set up by the linear speed of the piston at each 
point of the stroke. The air valve, governing the entry of 
the entire charge, is opened well in advance of the inner 
dead center of the engine, and is kept from closing until 
after the outer dead center, so that full effect of the mo- 



Tie Oas Engine 719 

mentum imparted to the entering gases at the highest rate 
of piston speed can be utilized without restriction, it being 
possible by such means to obtain a better filled cylinder. 

Compression. — Modern practice in gas engine design 
aims at securing the economical advantages coincident with 
high compression pressures, but the limit of allowable max- 
imum compression pressure depends upon the relative pro- 
portion of hydro-carbon gases, and hydrogen contained in 
the mixture or charge admitted to the cylinder. Hydro- 
gen will ignite at a much lower temperature than the other 
constituents, and owing to the additional heat during com- 
pression, it becomes necessary to so design the relative 
volumes of piston displacement, and clearance, that self 
ignition is practically impossible. With blast furnace gas 
containing only about two per cent of hydrogen, compres- 
sion pressures of 200 lbs. per sq. in. and* over may be 
safely used, and with producer gas, 150 to 200 lbs. are com- 
mon and safe pressures, but with illuminating gases the 
maximum is placed at 120 lbs. per sq. in. unless special 
precautions are taken to insure efficient cooling and clean- 
ing of the cylinders. This is effected by the injection of 
water or cold air through the clearance spaces and valve 
ports during the charging stroke, or by pressure during 
compression. 

Ignition. — The increase of compression pressures, and 
the use of poor gases for power purposes has brought elec- 
trical ignition devices into common use. Hot tubes of 
porcelain or hecnum are still used for engines designed to 
suit illuminating gas, but the impossibility of quickly ad- 
justing the instant of explosion when running, the rapid 
deterioration of timing valves, and cost of renewals have 
emphasized the superior advantages of electrical firing. 



720 Steam Engineering 

While with petrol engines the current from a primary or 
secondary battery is utilized with intensifying coil^ and 
jump sparking plug, the usual method adopted for gas 
engines is that of a positive break by mechanical separation 
of two electrodes through which current is passing from a 
magneto machine. In a magneto the lines of force flowing 
between opposite poles of a permanent magnet of great 
strength are alternately deflected from, and passed through 
an interposed armature by means of a shield or deflector 
operated by suita'ble mechanism from the half speed shaft. 
Upon maximum rapidity of the armature cutting the mag- 
netic lines of force a strong current is induced in the wind- 
ings and passes through a circuit formed by an insulated 
wire connected to a fixed, well-insulated electrode through 
the second and movable electrode in electrical contact with 
the engine frame and through this to the armature. It is 
of course very necessary to time the mechanism making the 
^^break^^ so that it synchronizes with the period of the most 
powerful induced current in the armature. Most of the 
difficulties encountered with magnetos have been owing 
to the slipping of the actuating mechanism from the coned 
seating on the armature spindle, but once the correct set- 
ting has been noted and marked, attendants Jiave found 
that very little other attention is necessary. 

Primary Batteries. — Those used are of two kinds, dry 
and wet batteries. Before the dry cell became so common, 
the cell that was used mostly for bells, and other open cir- 
cuit work, (by open circuit work is meant intermittent work, 
like a bell that rings occasionally, or ignition purposes; a 
closed circuit is one where the current flows continuously) 
was the wet sal ammoniac cell. The elements in this cell 
are commonly carbon and zinc; the earlier types had the 



The Gas Engine 721 

carbon contained in a porous cnp and surrounded bv broken 
carbon and the depolarizer^ but the later and more im- 
proved forms have the depolarizer compound mixed with 
the carbon^ and the whole formed into a cylinder^ while the 
zinc element is in the form of a pencil or rod about three- 
eighths of an inch in diameter and passes through a por- 
celain sleeve in the center of the carbon so that it is insu- 
lated from it. This form of zinc exposes very little sur- 
face to the solution^ and the internal resistance of the cell 
is high. Some makers have endeavored to overcome this 
by making a large sheet zinc^ which either encloses the 
carbon^ or is enclosed by it. This increases the amperes that 
can be drawn from the cell, but unfortunately, as there is 
no porous cup to help resist it, local action soon takes place 
and the cell soon runs down, even if it is not worked, while 
the small pencil zincs will stand for years; but their ampere 
output is low, from 3 to 6 at a voltage of 1.6 so that as a 
rule they are not as good as the dry cell for ignition pur- 
poses, unless connected in series parallel, when they will 
give good service. 

The Copper Oxide Battery is another type that is fre- 
quently used. This battery has elements composed of cop- 
per oxide compressed into a flat firm plate, and a zinc plate, 
both of which are suspended in a solution of caustic potash ; 
the voltage is very low, a little less than 1 volt per cell, but 
the amperage is very high. In fact, the batteries are sold 
on an ampere rating very similar to that of storage bat- 
teries. The ampere hours capacity of the cell determining 
its price (an ampere hour, is one ampere flowing for one 
hour, or its equivalent). These cells are usually arranged 
so that all parts fail at nearly the same time, that is, the 
solution is exhausted at the same time that the elements 



722 Steam Engineering 

are used up^ so at the end of each run all that is left is 
the jar and element holders. It shoiild be borne in mind 
when installing cells of this character^ that on account of 
their low voltage it is necessary to install one cell for each 
volt wanted. 

TJie Storage Battery is perhaps the best battery for 
spark producing purposes, as its voltage is high, starting at 
2 volts, and working strongly till towards the last, when it 
drops to 1.8 and should be recharged while its amperage is 
very high ; in fact, drawing current from a storage cell has 
been likened to taking water from a pail, one can get any 
quantity that it contains, from a drop at a time to the whole 
amount by tipping the pail over. In the same way current 
can be taken from a storage cell by regulating the resistance 
so that any amount can be drawn oil from .001 of an 
ampere, to several hundred amperes. 

A Storage Cell consists of several grids or skeleton 
frames of lead which are filled part of them with red lead 
for the positive plates, and the rest with litharge for the 
negative plates; under the action of the electric current, 
these turn into plain lead for the negative, and peroxide of 
lead for the positive. These are immersed in a mixture of 
sulphuric acid and water, about 6 parts of water to 1 of 
acid, and then subjected to the action of an electric cur- 
rent, and while they do not (as their name might indicate) 
^^store electricity^^ a chemical action takes place which 
renders them capable of giving off a large proportion of 
the current which they receive. 

A Dry Battery is not, as its name might indicate, dry ; it 
is, rather a moist battery, for as soon as it becomes ^^dry^^ 
its usefulness is ended. This is one reason why it is neces- 
sary to be certain that the batteries are new and fresh when 
buying them. 



The Gas Engine 723 

As commonly made^ a dry battery consists of a round 
zinc case^ which forms one of the elements^ and which con- 
tains a piece of carbon in the center that forms the other 
element. This carbon element is made in various shapes 
according to the manufacturer's ideas^ as each maker is 
striving to get as large a surface as possible in order to 
reduce the internal resistance of the cell and get a large 
output in amperes. The carbon is usually surrounded by 
some powdered carbon containing what is called the ^^de- 
polarizer'' (though this depplarizer may be incorporated in 
the exciting paste). This depolarizer has a great influence 
on the life of the cell for the reason that, under the action 
of the exciting fluid when the cell is working, bubbles of 
hydrogen form on the carbon and to quite an extent insu- 
late it, thus preventing the action of the excitant on it, 
so much so that it seriously weakens the action or output 
of the cell. The depolarizer to a great extent counteracts 
this by absorbing the bubbles and thus sustains the cell, 
keeping the output more nearly uniform. When a cell is 
"run down/' a rest allows this depolarizer to continue its 
action, and after a time the cell will be found in much better 
condition, though as both the exciting fluid and the de- 
polarizer are weakened, it will never be as good as before. 

The exciting fluid is a solution of sal ammoniac with 
other ingredients added. The precise formulas are kept 
secret by the manufacturers, but plaster of paris, mixed 
with oxide of zinc and other chemicals, which keep the 
plaster in an open and porous condition so that tlie excit- 
ing fluid and gases can easily pass through it, are used. 
This mixture is firmly packed in the space between the 
carbon and the zinc after a piece of blotting paper has been 
rolled up and placed next to the zinc to act as a porous 



724 ' Steam Engineering 

cup to prevent actual contact between the mixture and 
the zinc. 

The usual test for a dry cell is with an ampere meter^ 
and they are rated as to what they will show ; for instance 
one showing less than ten amperes is considered as poor, 
while one showing twenty-five amperes is considered excel- 
lent. This style of testing and rating, while it is the only 
convenient and quick way known at the present time, is 
not very reliable owing to the uncertainty as to the exact 
condition of the cell. According to ohms law, current in 
amperes equals electromotive force in volts divided by 

^ E 

resistance in ohms; expressed by the formula C = — . Now 

the internal resistance of the cell may be high, and the 
result is that when drawn upon for current this resistance 
will restrict the volume of flow to a low reading on the 
ammeter, or if the internal resistance of the cell is low a 
larger volume of current will flow, and the reading of the 
ammeter will be higher, while the voltage remains the same. 

Of course the low reading may just as well come from 
the cell not being in good condition and having very little 
in it. While on the other hand the low internal resistance 
and high reading cell is exposed to the dangers of local 
action, that is, the current works inside of the cell itself, 
wearing it out while standing in much the same way that a 
leak might start in a pail of water if the sides and bottom 
were extremely thin. 

Another element of uncertainty lies in the internal 
resistance of the ampere meters used for testing. If the 
resistances of its working coils are low, it will show high 
reading, if they are high the readings will be low, for the 
reason that the small voltage of the cell cannot push the 



The Gas Engine 725 

heavy cnrrent through against the high resistance of the 
meter; some meters are supplied with a conducting cord 
to reach across where it is difficult to get at the cells. A 
decided difference in the reading will be noticed when us- 
ing this cord for the same reason spoken of above, as the 
resistance of the cord, while it is small, cuts down the 
current very appreciably. While the high resistance me- 
ters are not favorites with the battery dealers, for the rea- 
son that they do not show amperage enough, they are the 
best for practical use as they do not draw so heavily on the 
battery, and as soon as one gets accustomed to how low 
cells can be worked, according to their particular meter 
reading, it matters very little what that reading is, provid- 
ed that it does not change. 

One trouble with the common cheap meters is, that they 
depend for their accuracy upon the difference in pull be- 
tween a permanent magnet and an electro magnet which 
is energized by the cell to be tested, , As long as tlie strength 
of the permanent magnet remains the same, the reading 
remains the same, but as the permanent magnets are us- 
ually made from cast iron, the magnetism does not remain 
the same, but it is continually getting weaker. As the 
electro magnet remains practically the same, this allows it 
to pull the needle further and further as the permanent 
magnet weakens more and more so that the readings are 
continually getting higher and higher; for this reason it 
is well to have the meter tested occasionally in series with 
some large standard make. 

From the foregoing it can be easily seen that all connec- 
tions should be kept clean and tight, for dirt adds greatly 
to the resistance that the battery has to overcome. A dirty 
connection is a hard trouble to find at times when the wir- 



726 Steam Engineering 

ing runs through obscure places as it usually does around 
ordinary gas engines. A loose connection will also cause lots 
of trouble and be difficult to find for the reason that it 
will work at times, and not at other timeS;, gi^'ing otlq the 
impression that the trouble may be in the carbureter, or 
^plug. 

Magnet Ignition. — There are three types of magneto 
ignition. The most recent type is the inductor type of 
magneto, which has no moving wires, commutators or 
brushes and which generates a sine wave of alternating 
current. 

The second type is a dynamo type of magneto, which has 
a commutator and brushes, and a little drum wound ar- 
mature, and which has a permanent magnetic field. This 
type of magneto is merely a dynamo with permanent 
magnets instead of electric magnets for its field. 

The third type is an alternating current magneto which 
is equipped with its own circuit breaker and distributor, 
commonly called a high tension magneto. This type of 
magneto is also often made with a circuit breaker and 
distributor, and a primary winding on it, which operates 
on a coil, external to the magneto. It is a low tension 
magneto, but is also frequently called a high tension mag- 
neto, on account of its producing a jump spark. 

Spark Coils. — Soft platinum points should not be 
used but an alloy of such percentage of iridium and plat- 
inum as will permit a very hard and dense point, and one 
which will not weld itself together as soon as it warms up. 
It must be borne in mind that pure platinum is a very soft 
and spongy metal, and will weld together at temperatures 
extremely low for welding heat. 

Irido platinum contact points require a very much higher 
temperature before they will weld or seize together. 



TJie Oas Engine 727 

In the construction of spark coils the very best of in- 
sulating material should be employed, and after the wind- 
ings are made, they should be pumped out in a hot vacuum, 
thus exhausting all of the air and moisture and they should 
then be impregnated while tinder vacuum with a dielec- 
tric of heat and moisture resisting qualities, which would 
seal up the windings, making them impervious to mois- 
ture, and preventing all electrical discharges and leakage 
between its turns and layers. 

This method of treating spark coils is quite recent, and 
is by no means as yet universal among the various spark 
coil builders. If spark coils were all built properly, with 
the proper kind of windings, and the proper kind of 
vibrators used, and the coils used in connections with the 
proper kind of timers, that is, timers which do not have an 
unnecessarily long period of contact, it would be found that 
the battery consumption could be reduced very materially. 

Proper timing of ignition devices has a direct result 
upon the economical working of the engine. If the mech- 
anism is set too early on the compression stroke, combustion 
of the charge occurs at, or before the inner dead center of 
the engine, resulting in violent shocks, excessive strain 
upon the piston, connecting rod, and bearings and in- 
volving great waste of power. If too late, the piston has 
commenced to accelerate under the influence of momentum 
stored up in the flywheel, so that .the explosive force follows 
the piston without attaining its maximum thrusting effort, 
and with some loss of compression pressure, due to the re- 
expansion of the charge before ignition is effected. 

The speed of flame propagation varies with the per- 
centage of hydrogen contained in combustible mixtures, 
and it is convenient for means to be provided to adjust the 



728 Steam Engineering 

instant of ignition to suit varying qualities of gas. For 
this reason many makers fit a device permitting an attend- 
ant to set the ^^break^^ at the most suitable instant, and 
there is no doubt that with such facilities a careful man 
can thus obtain good results even with very variable mix- 
tures such as often occur with poor gases generated by pro- 
ducers. Some leading manufacturers^ however, realize 
that, by carelessness or neglect, the provision of such means 
of adjustment is liable to misuse, and they prefer to ar- 
range two firing points only — one very late for starting up 
at slow speeds, and another for normal speeds, the varia- 
tions in inflammability of charges being deemed of less 
importance than the variations of the average skill and 
intelligence of attendants. 

The Explosive ilfta:^i^re.*— ^^Theoretically, ignition must 
be effected early enough and be so efficient that the whole 
of the power charge is ignited when the piston reaches the 
inner dead center position. Thus the condition of max- 
imum heat development will occur with the minimum 
cooling surface, and in a space which is specially designed 
to withstand high temperatures and pressures. Purity, 
calorific value, tem_perature and compression of the mix- 
ture, as well as the position and efficiency of the sparking 
apparatus, the form of combustion chamber and other con- 
ditions, will cause inflammation to spread faster, or slower, 
which phenomenon becomes quite clearly visible on the 
indicator card, provided the latter be taken on a drum 
with continuous travel. 

In several types of large modern gas engines the point 
of' mixing the gas and air is rather superficially treated, 



* Franz Ehrich Junge. ii 

m 



The Oas Engine 729 

while Keichenbach^ who certainly deserves consideration 
as an authority on the subject^ puts very much emphasis 
on this feature in all his designs from the earliest down 
to the very latest. It is interesting to examine what has 
actually been done to clarify this question^ and which view 
the serious student of the gas problem is justified in 
holding. 

Gas and air properly mixed in chemical proportions, so 
that just sufficient oxygen is present in the combination to 
ensure perfect combustion, will give the highest temperature 
of explosion which it is possible to obtain. Above and be- 
low this ideal condition there is a wide range of inflamma- 
bility wherein more or less oxygen in the form of air may 
be mixed with the gas, than is necessary for its chemical 
combustion, so that a mixture of such composition will yet 
ignite but will burn at a slower rate of flame propagation 
and, consequently, will not develop the maximum tem- 
perature corresponding to its calorific value. If with a cer- 
tain gas there be mixed about 4.7 times the amount of air 
that is necessary to establish the condition of chemical 
balance, the ihixture will be that which is theoretically 
best suited for adoption in gas-engine practice. Theory 
and practice often differ, and so it is found advantageous 
to employ in actual practice far more air in the internal 
combustion process than is theoretically required. The 
reasons are threefold: To reduce temperatures all round, 
to prevent premature explosions which might be provoked 
by the high heat of compression, and to supply to the gas, 
even when poorly mixed with the air, always sufficient 
oxygen for combustion, and consequently to reduce the loss 
' of unburnt gases leaving the exhaust to a minimum. 

If one examines by thermodynamic calculation the com- 
bustion efficiency of lean mixtures under whatever cyclic 



730 Steam Engineering 

conditions they may be transformed into work^ it will be 
fonnd that maximum economy is attained by compressing 
the weakest mixture to the highest possible degree^ bnt here 
again one is confronted by an upper limit which is rigidly 
drawn by the lack of inflammability of snch mixtures. 
Desire for thermal excellence of the working process forces 
us to approach this upper limit as much as possible^ but the 
decreasing calorific value of the power charge per unit of 
contents^ and the decreasing capacity of the engine keeps 
the actual practice far below this extreme ideal. In 
average practice it is customary^ at normal loads and with 
lean gases^ to work with a surplus of air of from 30 to 40 
per cent over what is theoretically required; with gases 
of high heat value^ even more air is provided^ so that the 
dynamic medium in the engine cylinder possesses a calor- 
ific value of from 44 to 62 B. t. u. per cubic foot.'' 

Explosion and Expansion. The mean pressure upon the 
area of the piston throughout the stroke is^ of course^ of 
great importance and directly affects the power given out 
from the engine. High initial explosion pressures per se do 
not create the most powerful efforts behind the piston^ 
neither are low terminal expansion pressures indicative of 
maximum economy. 

Exhaust. Before the expansion^ or power stroke is fully 
completed the exhaust valve commences to open — usually 
when the piston has still to travel one-tenth of its stroke. 

On small high speed engines the exhaust valve should 
open 15 to 40° before center on the power stroke depend- 
ing on the size and the speed of the engine. The last part 
of the power stroke is not noticeably effective in delivering 
power to the crank shaft and the exhaust valve is opened 
early to get rid of the heat after it has done its work. In 



Gas Engine Valve Setting 



731 



an engine with 6-incli stroke the piston travels only {^ 
inch in the last 40° of the power stroke as shown in Figs. 
303 and 304. The exhaust valve should never close before 
dead center on the scavenging stroke. 




For slow moving engines with large^ easy valve ports 
and passages, the exhaust opening may be fixed at 15 to 20° 
before center instead of 40°, and the inlet opening and 
closing points may be fixed at center to 10° after center. 



732 



Steam Engineering 



For very high speed engines the inlet closing should be 
delayed to 30 or 40° past center instead of 20^ as shown. 
A point to keep in mind is that it is impossible to change 
the time a valve opens without changing the closing time 
correspondingly earlier or later^, unless a new cam of dif- 
ferent design is used. This is indicated by A and B, Pig. 
303. If;, for example, it is desired to open the valve later 
without changing the closing point at B, the cam must be 
made so the beginning of the lift at point A will be carried 
around further toward B. 



£x7i(wst valve closes 




InUtTmlve o j pensj 



^ExTioust valve 



Fig. 304 



If an engine is known to be properly timed and is to be 
taken apart it will save much trouble later, to see that the 
gears are marked as shown at C, Fig. 303, before taking 
the machine to pieces. The gears can then be readily 
reassembled and the timing will be just as before. The 
terminal expansion pressures are about 25 to 30 lbs. I 
above atmosphere, and the velocity with which the burnt | 
product leaves the cylinder due to such pressure imparts | 
considerable momentum to the column of escaping gases, j 



Gas Engine Valve Setting 733 

thus helping to effect their thorough evacuation. With 
long exhaust pipes not unduly restricted, the energy of the 
moving column of gases is taken advantage of. 

Valve Timing. — Timing the valves of a gas engine means 
practially the same thing as "setting^^ the valves of a 
steam engine. It means to so set the gears, cams, and con- 
tributory adjustments that admission and exhaust valves 
will be opened and closed at a point a certain number of 
degrees from dead center in the travel of the crank, and 
with relation. to the piston stroke. The first thing, there- 
fore, is to know positively just when the crank is on the 
dead centers. The piston is, of course, at the extreme ends 
of its sroke when the crank is at dead center. Owing, how- 
ever, to the fact that the crank moves a number of degrees 
on each side of the center without perceptible movment of 
the piston, it is impossible to tell accurately when dead 
center is reached by watching the position of the piston. 
Guess work will not do. 

The following instructions apply more particularly to 
the smaller sized, high speed engines. Large sized engines 
will be taken up later on. 

Pig. 305 illustrates a simple, accurate method of finding 
the dead centers. First provide a stationary pointer on 
the engine as at C. It will be better if this pointer can be 
arranged close to the face of the flywheel. As the flywheel 
is keyed securely to the crank shaft its movement corre- 
sponds to the movement of the crank. Now turn the crank 
to one side of center as shown by the full lines in the- 
drawing; insert a rod. A, through a hole in the head letting; 
it rest firmly against the piston ; make a mark on the face 
of the flywheel at D as indicated by the stationary pointer,. 
IC; also make a mark, B, on the rod, A. Now turn the: 



734 



Steam Engineering 



crank to the other side of center as shown by the dotted 
lines ; when the mark^ B, on rod A^ is at the same position 
as before with relation to its guide, and to the piston the 
crank will be at exactly the same distance from center as 
before ; now make the mark, E, on the face of the flywheel 




Fig. 305 



as indicated by the pointer C. As marks D and E are at 
equal distances on each side of center, it follows that in 
bisecting the distance from D to E, as shown, and bringing 
the central mark, P, to the fixed pointer, C, we will bring 
the crank to the exact dead center for that end of the stroke. 
The opposite center is found in the same way. After the 



Gas Engine Valve Setting 735 

dead center marks are made on the flywheel the stationary 
pointer, which is left permanently in position, will show 
at any time when the crank is on dead center. 

Fig. 305, shows valves in the head one of which has been 
removed to insert the rod, A, for finding the exact dead 
centers. The valve stem guide makes a good guide for the 
rod. A, of similar size. Where the valves are not in the 
head, any other opening, as for spark plug or igniter may 
be utilized by making a special block to fit the opening and 
drilling in it a guide hole for the rod A. 

■ By measuring the distance in inches before or after the 
dead center mark on the flywheel to the point at which the 
valves open and close, the number of degrees can be quickly 
determined. For example, suppose we find the exhaust 
valve opening 10 inches (as measured in the face of the fly- 
wheel) before the crank reaches center on the power stroke 
of the piston. If the flywheel is 25 inches in diameter we 
have 25" X 3.1416=78.54: circumference of the wheel; 
(360° always represents the circumference of a wheel of 
any size) then we have 360°-^-78.54:=4.58° for every inch 
on the face of the 25 inch flywheel. If as stated the ex- 
haust valve is opening 10 inches before center we have 
4.58° X 10=45.8° before dead center at the end of the 
power stroke. The closing point of the exhaust valve and 
the movement of the inlet valve (if it is operated with a 
cam and gear) can be checked up in the same way. 

Owing to the fact referred to that the crank moves a 
number of degrees at the ends of its stroke without 
perceptible movement of the piston, there is a range of 15 
or 20° in valve setting within which it is difficult to detect 
material difference under equal conditions of port passages 
and engine speed. In fact it is the valve lift, size and 



736 Steam Engineering 

length of inlet and exhaust passages^ and the engine speed, 
or corresponding speed of the gas flow that decide the best 
valve setting for any particular engine. If the engine runs 
slowly^ and the inlet valve and passage are of ample size, 
the intake valve may open and close at dead center with ex- 
cellent results. If the incoming charge comes into the cylin- 
der at high speed, as is usually the case with high speed 
engines, a late closing of the inlet valve is necessary, because 
of the greater vacuum following the piston, and the inertia 
or moving force of the incoming charge. A late opening 
of the intake valve (from 10 to 20° past center) is recom- 
mended to secure better action of the carbureter. 

Relative Efficiency of Power Gases. Apart from the 
calorific values of one cubic foot of the various powergases 
when burnt in sufficient air to support complete combus- 
tion, it is necessary to differentiate them in terms of calor- 
ific value per cubic foot of gas and air mixture when only 
just sufficient air is present. For gas engines, however^ 
it is necessary to dilute the gas still further in order to 
control ignition as, varying with the percentage of hy- 
drogen present, theoretical mixtures are impossible, owing 
to risks of pre-ignition and violent shocks caused by the 
rapidity of the propagation of flame. Experience has 
determined that while hydrogen is of the greatest value in 
obtaining good results, yet it is important that its volume 
should be only about 7 per cent in gas engine mixtures. 

Gas Engine Indicator. — The principles governing the 
action of the gas engine indicator are precisely similar 
to those of the steam engine indicator which has 
already been described in the section on steam engines. 
The only difference between the two instruments lies in 
the details of construction, the gas engine indicator being 



Gas Engine Indicator 



737 



more strongly made in order to withstand the sudden shock, 
and higher pressure of that engine^ as compared with the 
steam engine. Firms manufacturing indicators make a 
combined steam and gas engine indicator^ the piston used 
for indicating gas engines being one half the area of the 
piston used for steam engines^ and as the same springs may 
be used with either piston^ the scale is doubled when the 




Fig. 306 



smaller piston is used. Fig. 306 shows a Crosby combined 
gas, and steam engine indicator with the small piston in 
place for gas engine work. The pencil arm is of extra 
strength to withstand the shock due to the explosive press- 
ure exerted upon the piston. The drum is of small dia- 
meter and extremely light to reduce the effect of inertia to 
a minimum. 



738 



Steam Engineering 



The tension of the drnm spring may be readily changed 
in accordance with the speed of the engine upon which the 
indicator is to be nsed. The initial vertical position of the 
pencil point with respect to the drum may be raised or 




Fig. 306a 

lowered on the paper according to the size of the diagram 
to be taken. 

Fig. 306'^ shows the new Crosby indicator designed for 
taking continuous diagrams. The drum is designed to use « 



Gas Engine Indicator 



739 



a roll of paper 2 inches wide and 12 feet long, upon which 
is made in the operation of the indicator a series of dia- 
grams. In the center of and concentric with the drum is 
a cylinder upon which the paper is wound as it is used. 
When the roll is exhausted, the cylinder can be withdrawn 
through an opening in the top of the drum and the paper 
easily detached. Above the cylinder is a knurled head 




Fig. 306b 



loosely attached to the drum spindle which can be adjusted 
to take continuous diagrams, varying in number from 6 to 
100 per feet of paper. 

Fig. 306b shows the Crosby reducing wheel with Detent — 
This detent when applied to the reducing wheel does not 
affect the connection between it and the engine; and does 
not allow the cord leading from the indicator drum to the 



740 



Steam Engineering 




UkIi 


Hiiii 


fe&wf M':iS-»aS;w; JW^ V 



Fig. 307 

tabor indicator with outside spring 

Combined Steam and Gas Engine Type 



Gas Engine Indicator 



741 



reducing wheel to slacken. When the clutch is thrown in, 
the indicator drum is revolved to the end of the stroke and 
held there by the drumcord, while the mechanism of the 
detent controls the cord leading from the reducing wheel 
to the cross-head of the engine. 

When the clutch is released, and the motion of the engine 
is again communicated to the drum, the latter takes up the 



Fig. 308 

motion without shock from the point where it stopped, 
because it starts from a state of rest at the end of the stroke. 
This is important, for if a drum is stopped and held by a 
detent in mid-stroke, where the piston is running at its 
highest speed, at the release of the detent, the drum will 
necessarily start again at such highest speed with* a shock. 
Moreover, as such a detent must engage at the highest 
speed, it often fails to operate and always wears rapidly. 



742 



Steam Engineering 



Fig. 307 is the Tabor combined steam and gas engine 
indicator^ and is supplied with two sizes of pistons as in the 
case of the indicator just mentioned. The spring is placed 
outside of the indicator cylinder in order that the hot gases 
from the engine will not affect the temper of the spring, 
and thereby change the scale. 

Fig 308 shows the piston, piston rod, cap and spring, 
removed from the indicator for cleaning. 

Fig 309 shows the parallel motion, or straight line mo- 
tion of the Tabor indicator. The curved cam slot provides 




Fig. 309 



for a perfectly true vertical motion of the pencil, and fur- 
ther provides rigidity and tends to reduce vibration. 

This indicator is made with the regular lA-inch area 
piston and cylinder for steam, and is furnished with a 
secondary and longer piston of ^-inch area which operates 
in the upper portion of the cock tube, to give the necessary 
increase in range to the spring, for extremely high pres- 
sures. This style indicator can be made with either size 
standard drum. 

All indicators of this type, employing a pressure piston 
and spring, require careful calibration where extreme 
accuracy is essential. On account of the inertia of the 



Oas Engine Indicator 



743 



piston and pencil mechanism, and that of the oscillating 
drum, engines of very high speed cannot be indicated by 
the forms of indicator just described. They have been 
found to be reasonably accurate at speeds as high as 500 
revolutions per minute, although at this speed they can be 
used successfully only by experienced hands. 

Indicators for High Speed. — To overcome this objection 
and to be able to indicate engines of speeds as high as 2,000 
revolutions per minute or more, indicators employing a 
beam of light thrown upon a sensitive photographic plate 



ACETYLENE 

BURNEfi 
i -TUBE 




TOP or TRIPOD STAND 



Fig. 310 



are now used. In this case a small mirror is caused to 
move in two planes at right angles to each other, one move- 
ment being produced by the motion of the piston, the other 
by the pressure, which is transmitted through a thin steel 
diaphragm. The angular motion of the mirror is so small, 
and the parts so light that the effect of inertia become:^ 
practically negligible. 

Fig. 310 shows the general appearance, and Fig. 311 two 
sections of one type of the indicator referred to. This in- 
strument is called the Hospitalier-Carpenter Manograph 
and is manufactured in Paris. 



744 



Steam Engineering 



Some makers manufacture special heavy indicators with 
^-inch pistons to suit the pressures involved in gas engine 
indication. Springs from 80 pounds to 200 pounds scale 
are very efficient in recording expansion^ combustion and 
compression lines^, as these effects are all high pressure. 
If the low pressure lines, such as the suction and exhaust, 
do not show up to advantage when taken with high scale 
springs, low scale springs of from 10 lbs. to 30.lb5.,may be 
used for obtaining those lines. 



ftep£TiTioM necftANisif 




CNO VIEW SECTION 



TOP VIEW SECTION 

Fig. 311 
high speed engine indicator 

Diagrams from Gas Engines, — The process of obtaining 
indicator diagrams from gas engines being similar to steam 
engine practice, it is not necessary to repeat a description 
of it. Attention will therefore be devoted to several 
reproductions of typical diagrams from gas engine. Fig. 
312 shows a characteristic diagram from a four cycle engine. 
On the forward stroke of the engine the piston draws into 
the cylinder a charge of explosive mixture, the pencil of the 
indicator tracing the line A-B. It will be seen that this 
line drops slightly below the atmospheric line A-P. This 



Gas Engine Indicator 



745 



slight drop is due to the partial vacuum produced within 
the cylinder during the ^^suction stroke^^ of the engine. 
From point B^ the piston returns to its original position 
compressing the mixture in the clearance space, the indi- 
cator tracing the line B-C, which is known as the compres- 
sion curve. At this point ignition takes place with a sud- 
den increase in pressure, the indicator tracing the line 
C-D, which is nearly vertical. On the next or third stroke, 
the gases are expanded to point E, at which time the exhaust 



w- 




Fig. 312 



valve opens, the indicator having traced the line D-E, which 
is known as the expansion curve. At E there is a drop in 
pressure as the gases issue from the exhaust port and from 
E to A the gases are swept from the cylinder which causes 
a line to be drawn by the indicator slightly above the atmos- 
pheric line A-F, as shown. This completes the cycle. The 
vertical distance from the atmospheric line to point C is 
proportioned to the compression pressure above atmosphere ; 
the distance to point D is proportional to the explosion or 
maximum pressure, and the distance to point E is pro- 
portional to the release pressure. 



746 



Steam Engineering 



Figure 313 shows a card from a two-port two-cycle gas 
engine. It will be noticed that the suction and exhaust 
lines are absent, the suction stroke being completed in an 
enclosed crank case^ or a separate cylinder or pump. The 
exhaust takes place at A and requires about one-tenth of 



f€*aTioV 




AZ^as 



Fig. 313 



the stroke. The exhaust and inlet ports are covered^ and 
uncovered by the piston and are definitely fixed points. 

Figure 314 shows a very good diagram^ where combus- 
tion is very nearly complete/ the mixture of air and gas 
being practically correct. The ignition line points slightly 




Fig. 314 

to the right at the top^ and is nearly perpendicular. The 
exhaust is shown to open at the right time about ninety 
degrees of the stroke. The suction and exhaust lines run 
very near the atmospheric line, thereby denoting correctly 
proportioned inlet, and exhaust valves and passages for 
same. 



Gas Engine Indicator 



747 



Figure 315 shows a condition existing when the suction 
to the cylinder is in some way choked, the suction line of 
the card or diagram being away below the atmospheric line. 
This condition may be caused by the valve being too small, 
improper setting of the valve, too small an area of the suc- 




4aafafi 



Fig. 315 



tion pipe, which may be caused in some cases by too many 
bends or short elbows. 

In figure 316, the exhaust line is shown at too great a 
height above the atmospheric line, thus showing that the 
discharge of exhaust gases is choked. In theory, there 




Fig. 316 

should be no back pressure, during the exhaust stroke, but 
in actual practice a pressure is recorded, varying in differ- 
ent makes of engines. 

Back pressure as shown in the diagram figure 316 may 
result from the following conditions: The exhaust valve 



748 Steam Engineering 

being too small in area^ setting of valve incorrect^ too long 
an exhaust pipey too many bends or too small a diameter 
of same. 

If the compression curve B C, Fig. 312^ shows a lack of 
sufficient compression pressure and all other conditions 
are perfect^ this is probably due to leaky piston rings, 
valves^ or joints. 

Figure 317 shows a low spring card and gives the differ- 
ent lines. The suction line is shown starting at C^ the 
point where the exhaust line strikes the atmospheric line, 
and extending to the point A where the, compression line 
commences. 




The mean effective pressure of gas engme diagrams is 
found by precisely the same method as that pursued with 
diagrams from steam engines. 

Indicated Horse Power. — This is a computation based 
upon the mean effective pressure developed at each ex- 
plosion and is usually calculated from the same formula 
xised in connection with steam engines: 1. H. P.=: 

PLAN 

where P=mean effective pi'essure ; L=lenffth 

33,000 

of stroke (ft.); A=area of cylinder; N=number of ex- 
plosions per minute. This formula does not . discriminate 
between mechanical friction and losses in ^"^fluid'^ friction. 



Gas. 'Engine Indicator 749 

To get acurate results it is necessary to obtain the mean 
effective pressure after measuring the indicator diagrams 
recorded during both ^'^power^^ and ^^cut-out'^ cycles as also 
^^compression^^ and ^^suction^^ cards. 

It requires a considerable knowledge of gas engine prac- 
tice to make use of the above f o]<mula. What is needed 
is one that is more arbitrary and fits the majority of cases 
and^ moreover^ requires the use of only a few facts^ such 
as the diameter of cylinder^ length of stroke and revolu- 
tions per minute. Such a formula will be of great, value 
in estimating the probable power a gas engine should de- 
velop if well designed and properly built. 

Such a formula is given as follows : 

VXr. p m. 
I. H. P.= 

10,000 

which means that the indicated horse power is equal to 
the volume of the cylinder in cubic inches multiplied by 
the number of revolutions per minute and divided by 
10,000. The constant used varies frqin 9,000 t9 14,000, 
depending upon certain types of engines; 10,000 is an 
average figure to use for four cycle engines. The brake 
horse power will be from 65 to 85 per cent of the result 
obtained ; 80 per cent may be taken as an average : 
For example, a 6V2"x9" engine at 300 r. p. m. 'gave by 
test 7.2 horse power. 

The area of the piston is 33.2 square inches and the 
volume of the cylinder is 298.8 cubic inches; multiplying 
by 300 and dividing by 10,000 gives 9.0 indicated horse 
power, or for a mechanical efficiency of 80 per cent 7.2 
brake horse power. 

Economy of Gas Engines. — As fuel is ordinarily used, 
at present, for light, heat and power, the losses are so 



750 Steam Engineering 

great that^ of the total calorific value of the coal, less than 
5 per cent on an average is converted into useful work, 
while the largest and best power stations utilize only about 
10 per cent. 

With gas-engine-driven units^ however^ fuel economy is 
the distinguishing characteristic^ resulting in a delivery 
at the engine shaft of not less than 16 to 20 per cent of 
the energy contained in the fuel. 

Notably is this true of lignite coal, immense quantities 
of which are to be found in various parts of the country. 
The calorific value of such coal averages only about 8,000 
B. T. U. per pound as fired; but, when utilized in a gas 
producer and gas engine, it is possible to develop a brake 
horse power on less than 2 pounds of lignite. 

Owing to the difficulty of securing, with this fuel, proper 
combustion under a steam boiler, the gas producer offers 
practically the only means of using it on a commercial 
basis. 

The same is true of slack coal, bone coal, etc. 

A recent bulletin of the United States Geological sur- 
vey calls attenion to the possibilities of the producer gas 
plant, as above indicated, and states that lignite beds 
underlying from 20,000,000 to 30,000,000 acres of public 
land, heretofore supposed to be practically useless, are 
now shown to have a large value for power development. 
This is of particular importance to the West, making pos- 
sible a great industrial development there. 

Producers now made will also successfully gasify nearly 
all grades of bituminous coal, as well as anthracite, or coke. 

Additional Advantages of Gas Engines. — The standby 
losses during a period of idleness are practically negligible. 



Producer Gas 751 

and are included in the fuel estimate per brake horse power 
as given above, leakage losses are reduced and the smoke 
nuisance is abolished. 

In localities where the water supply is scarce, or of poor 
quality, a gas power plant offers additional advantages, 
and, by the use of cooling towers, the water consumption 
can be reduced to a very small quantity. 

PRODUCER GAS. 

Producer gas, whether from anthracite or bituminous 
coal, lignite, wood, charcoal, or coke, is remarkably uni- 
form in quality, and a very desirable gas if properly cleansed 
from dust, tar and sulphur. As practically all the combus- 
tible matter of coke and charcoal is fixed carbon, these 
fuels are most readily gasified, and on this account are 
favorite fuels for small gas plants of the suction producer 
type. Anthracite coal contains a small quantity of vola- 
tile matter, but is also a very desirable fuel, the gas requir- 
ing but little cleaning. Bituminous coal, lignite and wood, 
although giving a desirable power gas, at the same time 
yield considerable amounts of hydro-carbon vapors con- 
densible in the form of tar and pitch, the removal of 
which from the gas is attended with some' difficulty. 

Complete producer gas plant equipments may be had of 
several types, suited either to bituminous or non-bituminous 
fuels, and with, or without apparatus for the reclamation 
of by-products, such as ammonia, tar and other hydro- 
carbons. The majority of tliese systems are simple in con- 
struction and operation, and yield a net efficiency consid- 
erably in excess of the steam boiler plant. 

In localities where natural gas is not available, the pro- 
ducer gas plant affords a comparatively simple, and inex- 



752 



Steam Engineering 



pensive means of generating a suitable fnel gas. It is less 
complicated in its workings than the average steam plant, 
and its efficiency is higher, as will be seen by reference to 



Torcent oflBeat in Coat 




JPoroont cf Hoat in Coat 



Fig. 318 
comparative efficiency of gas and steam plant 

Fig. 318, which compares the net work obtainable from j 
coal in modern well-equipped steam and gas plants of 
moderate size. The producer transmits 75 per cent of the 



Producer Gas 753 

fuel energy^ the boiler 70 per cent; the gas engine delivers 
at the shaft 25 per cent of the energy supplied, the steam 
engine 13 per cent; as a whole the gas plant realizes over 
17 per cent of the fuel energy, the steam plant about 8 per ' 
cent. On this basis the gas plant could afEord to use fuel 
costing twice as much as steam fuel; as a matter of fact 
it can utilize fuel much cheaper and of such low grade as 
to be quite unsuited for efficient boiler working. 

The gas producer takes the coal, ignites it, and by sup- 
plying a limited amount of air, and a proportionate amount 
of water keeps the fire at a dull red glow, just the right 
temperature to produce a good uniform quality of gas and 
prevent formation of clinkers. As the load on the engine 
is varied a greater or lesser quantity- of gas is required but 
it is' important that the quality or heat po^er remain the 
same. 

At present three distinct types of gas producer are offered 
to the power user. They are the suction producer, the 
steam-pressure producer, and the induced down-draft 
producer. 

The Suction Producer. — ^In this type the fuel is fed into 
the generator from a hopper at the top. Ashes and clinkers 
are removed from the bottom, and air is usually admitted 
below the gratc^ first passing through economizers, where 
it is heated and passed over a body of hot water to absorb 
the necessary moisture. In some makes of producer the 
air is admitted direct from the engine room, and a small, 
regulated amount of water is fed into a space prepared 
around the grate, where it is evaporated and is carried as 
steam along with the air up into the fuel bed. 

In this type of producer, coke or anthracite coal can 
only be used and not even these fuels in the very small 



754 Steam Engineering 

sizes. It is not easy to note the condition of the fire, as the 
generator cannot be opened at the top without admitting 
air and causing a poor mixture of gas ; the only thing to do 
in this emergency is to feed in more coal to stop the chim- 
ney holes in the fire-bed, or quickly insert a" poker bar and 
thoroughly tamp the fuel. The latter is the better way, 
even though it has to be done blindly. 

In operating this type of producer, trials and tribula- 
tions may be many and varied, depending largely upon how 
the producer is made and the basis of its horse power rat- 
ing. A suction gas producer rated at more than 12^/^ 
pounds of coal per square foot of grate area, or area of fuel- 
bed cross-section, is very apt to be too small, and a pro- 
ducer so small for the power it has to develop that it must 
be driven to furnish sufficient gas will immediately develop 
clinker troubles, variable gas troubles or excess CO2. If 
an attempt is made to correct clinker troubles with an over- 
supply of steam, an excess of hydrogen will result, with its 
attendant engine difficulties of back-firing, or prenlature 
explosions. 

Even with a producer of the proper size, the regulation 
of the volume of steam or water to the volume of air must 
be closely watched. Too frequent raking of the fire will 
waste good fuel, and induce draft holes through the fuel 
bed. Too much poking from the top will pack the fire, 
and necessitate an increased vacuum. Too fine a fuel will 
produce the same troubles, and any coal that fuses easily 
will not do for this type of producer. Anthracite running 
high in slate mixture tends to run high in sulphur, and 
high sulphur with slate makes bad clinkers at any time, 
and if the fire is forced at all will soon necessitate a shut- 
down to clean out. The producer should be of ample size 



The Gas Producer 



755 





mm0-¥-:-^^rrim:mm 


«■ 




■ ^ 11 


■■■;■: 'm 


.': P?^. 


^^^IHShMw.*....^^^! 












■ ''" y^^^^^' ' ' 






' ' ■ '''U 


:|,^^.p..,,;^i^^ 


\ 


■;.. f'^^'^^^Kr. \ 


■ 1 






ftf' "^^^B^ ■ ^ 






\Z->::Wm 


¥^ ^-. fg;- ^^% :s ,> '.^ 




Ij ^::^^fc:| 




' ■ "M 


U-^''i' 1 


■■ f: ^I'^c 




'w'^^^mi 




■/vp 


i;.- M -X. 


-.,i'^^ i ■' 




M- :m^^MM.- 




r^;p 


Xy/ji 


mmiB- ■r"u-:i 




H V ■ "^s^^^^pKI 




■ ■ ■"' W 


■;^;ii:'^ 


9^^^^^^$'^^! 


1;.; :, 


■1 






. ff^iJ 


m- ■ ^........^^mi 


t' 


-T'T"-" ■ • --■"■«?^^S^^S^3*^ 




:;::r:': ■■ \.-:v^tH|^^^^^^^^y 


1: 


t^ '■■' ''^*'^^^^^^P5^% 




' 1 


'S3©! "'''"^^^ 


MM^^-- ' f 


^^te* 


i K&^^^^^^S''-' 






«?f*P 


■K:.'. i 


^1 


ps^'i^^^^M-' 






Ir. ,.- . :!- ./yifS 


"^^^' - ^S^^^^^^^^^^m 


^^■# 


R ^^-'--s^^^^^^^Rwfsf 




■ "^ 


: V ,||: 


mJ^Km 




Ik -'.■ 






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B'-i 


Pill 


11 


■ :!y 




^^pr.jjf 


f^w*'-- 


^^^^r^"^/|^.. 


>«^# 


-^^""^{i^^^^^^ 


B ' ■■-^^^^':vyc _^^M««^ 


a §,.!' ^R 


&'' 


P# 


m^^^^i^:''?-: .- v/-J| 




^r; .-^1 " 


f ' f 


^k^iJpi.;, 


H^PI^R^l-; ' ,',' '■ ;^|^ 


^^^^^^|K^ii«>i ": ■ ^B 


p!%. ■ .:"■'' 


^^■■ 


'"til 


Ifera^^ii^:^ 


^afeii 




J . -;:; 


^^^fl 






Fig. 319 








MONAHA 


N SUCTION PRODUCER 






— 10 pounds of coal per 


square foot of internal area- 


-and 


rated on 


114 pounds of 


coal ] 


3er hor 


?e power 


hour. 





756 



Steam Engineering 



It is not; good practice to use a suction gas-producer 
plant -of over 150 horse power when the engine has to 
draw the gas from the producer by the vacuum in the 
cylinder. Sizes larger than this should be equipped with 
exhaust fans which will relieve the engine of this work^ the 




Fig. 320 
sectional view of monahan producer 

exhausters being driven by motors, or other auxiliary 
power. 

The Monahan Suction Producer. — This producer, a full 
view of which is shown in Fig. 319, is of the suction type, 
and consists of the usual generator, scrubber, and equalizing 
tank. The vaporizer for supplying steam to the fuel bed 



TTie Gas Producer 



757 



is an Tipper extension of the generator^ but is located so 
that the hot gases from the fuel bed do not impinge square- 
ly on the bottom of the vaporizer. This is clearly shown in 
the sectional view^, Fig. 320^ in which the revolving grate^ 
and air heater are also shown. The scrubber is of the wet, 
coke-filled type^ and the equalizing tank is a simple drum 




got Ate 

Inlet 



_8.teaia 
~ Inlet 



Fig. 321 
steam regulator 



and 



within an equalizing chamber formed in its cover, 
separated from the drum by a rubber diaphragm. 

A small vent in the cover allows air to pass in or out 
slowly, forming a sort of brake on the fluctuations of pres- 
sure within the drum. The regulator controlling the ad- 
mission of steam to the fuel bed is shown in section in 
Fig. 321. The outlet at the bottom is connected to the 
ash pit of the generator. The upper intake admits air 



758 



Steam Engineering 



only, and the intake near the middle admits steam. When 
running light the suction is insufficient to pull down the 
valve, and air alone passes through the fire. As the load 




Fig. 322 
smith automatic suction gas producer 

increases, the increasing suction gradually pulls down the 
valve (which is a piston valve) until the steam ports are 
uncovered to an extent depending upon the load. This 



The Gas Producer 759 

arrangement prevents the chilling of the fire with steam at 
very light loads^ and graduates the supply for heavier 
loads. 

Smith Suction Producer. — Fig. 322 shows a view of the 
Smith Automatic Suction gas producer^ built by the Smith 
Gas Power Co.^ Lexington^, Ohio — Fig. 323 is a sectional 
view of the regulator^ which is also shown in perspective 
in Fig. 324 mounted upon the superheater with which this 
producer is equipped. The hot exhaust from the gas engine 
is piped into this superheater which heats the incoming air 
for the producer and turns the proportionate amount of 



lVa/er/>^^ 




Fig. 323 

water required into steam. The regulator consists of a 
curved iron tube E through which the air is drawn into the 
superheater^ then on and through the fire bed in the pro- 
ducer. Vane V, Fig. 323^ is located in the curved tube 
and is connected to water cylinder G which is mounted on 
knife edge bearings so it will rotate freely. The vane V 
and the connecting arm H are accurately balanced by the 
adjustable weight K. Weight L serves to counteract the 
pressure of the air which passes with more or less force 
(according to the needs of the engine) through curved 
tube E. The water cylinder G is supplied with a needle 



760 Steam Engineering 

valve feed at N and an overflow next to its axis. The feed 
water from needle valve N runs directly into the air 
passage E. 

It will be readily seen that when more air is passing 
through the curved tube E the vane V will be drawn down 
rotating water cylinder G. As the water keeps its level 
there will be more head water above the needle valve feed 




Fig. 324 
N", causing an increase in the water feed in proportion to 
the increase of air. When the load on the engine runs 
light, and less air is drawn through tube E, there is less 
pressure on vane V, and the weight L rotates water cylinder 
G in the opposite direction, decreasing the head of water 
on needle valve N. The proportion of water and air under 
all the varying conditions is thus automatically held uni- 



The Gas Producer 761 

form. As the flow of the column of air passing through the 
curved tube E, and past vane ¥ is practically constant there 
are no sudden fluctuations of the vane and water cylinder 
but a smooth gradual adjustment to meet the any changing 
conditions. 

This machine is arranged to operate either up draft 
or down draft as may be required, and can be utilized on 
anthracite, semi-anthracite, coke, charcoal, lignite, wood or 
bituminous coal, as conditions may require. The machine 
is a straight suction producer and is complete in all par- 
ticulars as shown in Fig. 322. The gas pipe, at the upper 
left hand corner passes directly to the engine. 

The Steam-Pressure Producer. — This type has an upward 
draft, the air being drawn in around a steam jet through a 
Korting nozzle of the Bunsen type. Anthracite and coke 
are the only kinds of fuel available, unless tar extractors, 
and other expensive mechanical auxiliaries are provided to 
clean the gas. When the producer is equipped with such 
cleaning apparatus, bituminous coals or fuels containing 
volatile hydrocarbons may be used, but as these are con- 
densed and washed out of the gas, the thermal efficiency of 
the producer is reduced to the extent of the loss of the heat 
units contained in the extracted hydrocarbons, which are 
the richest part of the fuel. 

With a pressure producer it is necessary to have gas- 
storage capacity, so that gas-holders must be provided 
regardless of the kind of fuel used, and these must hold 
ienough gas to run the engine while the fire is being poked, 
and the ashes removed. Coal is fed through a tightly clos- 
ing hopper on top of the generator, and ashes are removed 
from the bottom when the generator is not in operation. It 
lis almost impossible to poke, or bar the fire while the pro- 



762 Steam Engineering 

ducer is runnings as any outlet for this purpose will be 
flooded with burning gas escaping under whatever pressure 
the steam jet is maintaining at the time. 

Induced Down-Draft Producer. — In the down-draft pro- 
ducer the gas is drawn down through the fire by an ex- 
hauster or fan, and forced by the exhauster through the 
main to the point of use. There is probably more horse- 
power of these producers in use than in all of the others 
put together^ but they are mostly of large size and the 
plants only number about one-fourth of the total. 

Essentially these are bituminous-coal producers. They 
are operated with an open top, where the fire is seen by 
the operator, and any blow-holes or passages in the fire jit 
are easily closed by the use of the poker or taiAping bar, 
and fresh fuel is fed as necessary. The volatile hydro- 
carbons of the fuel, being distilled at the top of the fuel 
bed, mix with the in-drawn air and steam, and pass down 
through the bed of incandescent carbon, where they com- 
bine with the other gases and leave at the bottom of the 
producer, as a fixed non-condensable gas. , This combina- 
tion of gases then passes directly into the bottom of a 
vertical tubular boiler and out at the top, thence into the 
bottom of the wet scrubber, where the outlet is under water 
to form a seal and prevent the gas from returning to the 
producer. From the top of the wet scrubber the gas passes 
to the exhauster, and is forced through the dry scrubber to 
the gas-holder. 

The boiler, which is a part of the producer installation, 
supplies a large part of the steam necessary for the pro- 
ducer, and also the amount necessary to run the engine 
driving the exhauster. This steam is made from the heat 
given up by the gas in its passage through the boiler, and 



The Gas Producer 763 

all heat that is not absorbed by the water is delivered up 
to the wet scrubber. Once a week these producers have to 
'be entirely cooled down to be cleaned^ and as the steam 
pressure in the boiler is down at this timC;, an auxiliary 
boiler has to be provided to start up again. Sonie time 
during the week^ especially toward the last days^ the fuel 
'beds become so clogged with the accumulation of ashes and 
clinkers^ that water-gas runs have to be made every few 
moments; the load on the engine driving the exhauster 
increases, and both these conditions so increase the demand 
for steam that the auxiliary boiler has to be brought into 
use. 

For continuous 24-hour service with this type of producer 
it is necessary to have a spare unit^ in order that it can 
take the place of the one that has been in service for a week. 
A single spare unit in an installation of a large number of 
units does not add a very large percentage to the original 
investment^ but a spare unit to a single outfit nearly doubles 
the cost. The following timely suggestions regarding gas 
engine practice are presented by the Gas Power Section of 
the A. S. M. E. : 

''Engine Efficiency, Should be expressed in terms of 
effective heat value^ until a combined gas-vapor cycle comes 
into use. For the present, let us not confound a definite 
engine efficiency by introducing the indefinite factor of 
latent heat of water vapor. Engine efficiencies should be 
igiven for full, to half load at least. 

''Producer Capacity, The producer should be rated upon 
I its ability to gasify coal. It would be more accurate to 
rate on B. t. u. of standard gas, but this is impracticable. 
1 Should the builder desire to rate on a special coal, he might 
i insert a clause limiting some of the constituents. In speci- 



764 Steam Engineering 

fying sizes, a maximum as well as a minimum screen should 
be mentioned. A mixture of many sizes packs the producer 
as badly as a very small fuel. As a usual thing the flexi- 
bility of the producer will more than meet the overload 
possibilities of the engine. 

''Producer Efficiency. Can only be specified in terms 
of B. t. u. output, involving volumetric measurement, which 
it is usually impossible to determine except by calibration 
of the engine. As we are dependent upon the engine as a 
gas meter, we must be consistent, and determine the effi- 
ciency of the producer in like terms, that is, the ratio 
between heat output in standard gas, and heat input in 
fuel for the fire. 

''Producer Regulation. An important point is the prop- 
erty of the producer as regards the regulation of heat value 
of the gas, and its pressure as delivered to the engine. Qual- 
ity regulation is covered by the engine-capacity clause 
Vith gas of not less than so many B. t. u. heat value per 
cubic foot.^ 

"Hydrogen Content. This may be expressed as a per- 
centage by volume of the gas, a percentage by volume of 
combustible in the gas, a percentage of the heat value *of 
the gas per mixture, or a percentage by volume of the mix- 
ture. The last appears to be the most explanatory. The 
first conveys no impression of the commercial value of the 
gas. The second is better in this respect. The third pre- 
sents widely varying values.^^ 

ALLIS-CHALMERS GAS ENGINE. 

Figure 325 presents a view of a four cycle, double acting 
tandem gas engine as built by Allis-Chalmers Companay, of 
Milwaukee, Wis. This engine is using natural gas. Fig. 



Allis-CJialmers Gas Engine 765 

326 shows a four cycle double acting twin-tandem gas' 
engine by the same company. 

The distinctive features of the gas engines built by AUis- 
Chalmers Co.^ or those which appeal most strongly to engi- 
neers who have seen them in service^ are the extreme sim- 
plicity of design^ the solidity of construction^ and the quiet 
operation. Maximum overloads are handled as easily^ and 




Fig. 325 

allis-chalmers four-cycle, double-acting, tandem gas engine 

direct-connected to an allis-chalmers continuous 

current generator — natural gas used 



with the same freedom from vibration that characterize 
their operation under normal conditions; the engines turn 
their centers as quietly as a slow-running Corliss machine 
and with apparent indifference to the rapid changes in load 
which they are often called upon to sustain. 



._ 



766 Steam Engineering 

"While the engines are^ as a whole^, exceptionally rigid and 
heavy^ the weight is concentrated in the frame, cylinders, 
and tie pieces in the direct line of stresses to which an 
engine of this type is subjected. In the frame is illustrated 
the principal difference between European and American 
design. This frame is designed for a side crank, in place 
of the double throw crank which represents the standard 
practice abroad. The stresses transmitted to the frame in a 
side crank engine are very great, but, even in the largest 
sized gas engines, they are no greater than AUis-Chalmers 
Company has for many years successfully provided for in 
steam engine practice. 

The jaw, which is subjected to peculiarly severe stress, 
is made in a form to insure maximum strength of the cast- 
ing, and is further strengthened by two steel tie bolts car- 
ried above the shaft, which are made of sufficient size to 
carry their proportion of the load without appreciable 
elongation. This construction eliminates entirely any bend- 
ing stresses in the frame at this point. 

The engine frames for the 2,500 K. W. units weigh 
approximately 90 tons each, and one-half of each frame is 
buried in the foundation, in order to raise the floor line 
to a point which will make the slides on the valve gear 
readily accessible. 

The pistons and rods are water-cooled, water being in- 
troduced at the center and flowing forward to a discharge 
in the frame for the front piston, and backward to a dis- 
charge in the tail guide for the rear piston, each piston 
having its separate supply. For dismantling or for cleans- 
ing, the rod is made in two parts joined at the central slide, 
the rear half going out at the back of the engine and the 
other half going through the frame, which is made open 
at the top for convenience. 




Fig. 326 

allis-chalmers, four-cycle, double-acting twin-tandem gas 
engines, each of 2,000 h. p. capacity 
Driving Allis-Chalmers Alternating Current Generators in tlie 
Power House of ttie Milwaukee-Northern Railway, Port Wash- 
ington, Wis 



768 Steam Engineering 

The Valve Gear. — On twin tandems the valve gear is 
located between the engines, concentrating it in such a way 
as to make it very convenient for the operating engineer. 

This gear is of Allis-Chalmers Co/s stratification type, 
and the engine operates with constant compression, thus 
tending to insure smooth running under the highly varia- 
ble loads to which it is subjected. The inlet gear is ex- 
tremely simple, consisting of a main inlet valve of the 
single beat poppet type, eccentric operated, thus insuring 
long life and quiet running. The mixture of the air and 
gas is thoroughly effected before entering the cylinder by 
means of a patented annular mixing chamber located under 
the main inlet bonnet; the design and operation of this 
device is such that, at the instant of closing of the main 
inlet valve, there is practically no explosive mixture left 
outside the cylinder. The gas valve is of the double beat 
poppet type, controlled by a variable lift rolling lever 
operated by a single link connection to the main inlet, the 
lift of the valve and consequently the amount of gas ad- 
mitted, and the time of admission being regulated by the 
governors. The exhaust gear is of the single beat poppet 
valve type, eccentric operated, and is in this respect a 
duplicate of the main inlet gear. A feature of this engine 
is the location of the exhaust bonnet with its valve at the 
bottom of the cylinder, where all the dirt is removed by the 
action of the exhaust gases, and the provision of a substan- 
tial jack to lower the entire exhaust mechanism out of 
place to allow inspection and regrinding of the valve, which 
also serves to swing the valve chamber, with the valve and 
its operating mechanism complete, out to one side where it 
can be reached by the crane hoist. The removal of one pin. 
either in the inlet, or exhaust mechanism, is all that is 



AUis-Chalmers Gas Engine 769 

necessary to allow the removal of either the inlet or exhaust 
bonnetS;, with their valves and entire operating apparatus^ 
without disturbing any adjustment whatever. 

The igniters are electrically controlled^ and so arranged 
that the time of ignition may be regulated by a single hand 
wheel. Direct current at 80 volts is used in the ignitioi. 
system. Duplicate independent igniters are provided at 
each end of the cylinder to insure prompt firing of low 
heat value gases^ and also to avoid the danger of shut down 
due to short circuit. 

The air starting device consists of a small poppet inlet 
air valve at each end of each cylinder^ operated by the 
layshaft. Air is admitted to each cylinder in turn at what 
would be the working stroke. As the high compression 
carried prevents the engine from stopping on the dead 
center^ this arrangement insures the prompt starting of 
even a tandem engine without the use of a tarring gear. 
These engines being twin tandem will^ of course^ start from 
any position. 

Lubrication. — All wearing surfaces^ including the main 
bearings^ slides^ crank and cross-head pins^ are arranged for 
a continuous oiling system and the cylinders are lubricated 
by carefully timed admission of the cylinder oil^ sight-feed 
oil pumps being used. 

The engines shown in Fig. 326 are of the following 
dimensions: Each engine has four cylinders 32 inches in 
diameter by 42 inches stroke^ and operates at 107 revolu- 
tions per minute. Each unit is rated at 1,000 K. W. but 
both engines and generators were designed for large over- 
load capacities. 

The engines shown in Fig. 302 are said to have the larg- 
est cylinder diameter of any gas engine yet built in the 



,„ 



770 



Steam Engineering 



Uxiited States^ the dimentions being 44 inches diameter by 
54 inches stroke. 



•in;: . 



WESTINGHOUSE GAS ENGIN'E. 



Figs. 327 and 328 show respectively front and rear views 
of the AVestinghonse gas engine of the vertical type. These 




Fig. o'U 

WESTINGHOUSE THREE-CYLINDER VERTICAL GAS ENGINE 

Front View — Direct Connected Type 

builders also manufacture a horizontal heavy, duty double 
acting type of gas engine of large capacity. 

Fig. 329 is a vertical section through one of the West- 
inghouse cylinders^ showing the gas and air distribution, 
water jacket, and also shows the valve gear. The inlet and 
exhaust valves are located at opposite ends of the vertical 
cylinder diameter, as shown in Fig. 329. Both valves, at 



al^ 



W estinghouse Gas Engine 



111 



each end of a cylinder, are operated by a single eccentric 
through wipers and rocker-arms; this construction is also 
shown in Fig. 329. The exhaust valve is of the mushroom 
type, hollow, with a tube extending up the stem into the 
center of the head for discharging the cooling water; the 
water is introduced through the annular passage between 




Fig. 328 

westinghouse three-cylinder vertical gas engine 

Rear View — Belted Type 

the outlet tube and the wall of the valve-stem. The valve 
page sets into a circular housing projecting downward from 
the cylinder. 

The main inlet valve is of the simple disk type, and is 
opened and released by the eccentric and wiper levers 
[always at the same points of the piston travel. There is 
mounted on the valve-stem, however, a cylindrical valve 



772 



Steam Engineering 



sO^ Beach Bodt 




Jig. 329 
valve gear, westinghouse gas engine 



Westinghouse Gas Engine 773 

which controls the quantity of air and gas admitted^ this 
being under the control of the governor. It is not shown 
in Fig. 329^ but the connection for the governor rod is 
shown. The cylindrical valve fits closely in the bore of the 
valve cage^ and has ports in its wall which correspond to 
the ports leading into the cage from' the air and gas pass- 
ages. When the admission valve is on its seat^ the ports 
in the cylindrical valve are above those in the cage wall^ 
and the latter are therefore closed^ preventing gas from 
backing up into the air passage. When the inlet valve is 
depressed by the valve-gear^ the cylindrical valve goes with 
it^ and its ports then come into horizontal alignment with 
the air and gas ports in the wall. The governor controls 
the quantity of air and gas admitted by rotating the cylin- 
drical valve on the disk- valve stem; in the full-load posi- 
tion the ports are all in exact alignment when the valve is 
depressed^ and at lesser loads the valve is twisted around by 
the governor so as to shut off part of the port opening. The 
four cylindrical valves of one side of the engine are all con- 
nected together by reach-rods^ so that the governor adjusts 
all four valves simultaneously and alike. The two sets of 
regulating gear are connected by double reach-rods^ so that 
there is no lost motion between the two sides. The pistons 
are centered in the cylinders by adjustments at the three 
crossheads. Each piston is equipped with four sectional 
packing rings; the sections of each ring are joined by brass 
keepers and set out by flat steel springs. The piston-rods 
are hollow^ of course^ to admit and discharge cooling water 
to and from the pistons^, and they are turned without any 
camber. 

Governor. — In the Westinghouse gas engine, regulation 
is obtained through two elements, governor and mixing 
valve. The flyball governor or regulator is geared direct 



774 ^ Steam Engineering 

to the main engine shaft. From the rise and fall of the 
governor sleeve^ with corresponding changes in speedy the 
essential motion is derived for operating the mixing valve 
through a simple and direct linkage. With this mechanism 
the governor is able to record without the least delay the 
slightest change m speed of the engine, due to change in 
load. 

A slight range in speed is desirable for parallel operated 
units. This is provided for by two springs on the mixing 
valves, which can be adjusted while the engine is running, 
so as to alter the position of the governor. 

Mixing Valve. — This important detail part accomplishes 
in a single mechanism two fundamental functions — one, the 
proper proportioning of air and gas, and the other, the con- 
trol of the quantity of mixture delivered to the cylinders. 
A vertical free moving cylindrical valve with suitable ports 
is surrounded by two independent sleeves, correspondingly 
.ported, capable of rotation by handles through a small arc 
as indicated by two graduated dials. By rotating these 
sleeves, when the engine is running on a certain kind of 
gas, it is easy to ^^feeP^ for the best mixture. The mixing 
valve then accomplishes the desired regulation as controlled 
by the governor. In producer gas plants, foreign matter 
such as dust and tar makes it difficult to keep this type of 
valve in working order, so that a poppet type is used in- 
stead, operating on the same principle. 

In the Westinghouse engines the ^'^make and break'' or 
^^hammer break'' type igniter is employed, this type having 
been found by experience to be the least susceptible to irreg- 
ular working, and to give the longest life. Essentially the 
^^make and break" system, comprises a source of electrical 
current and a spark plug, inserted through the walls of the 



Westinghouse Gas Engine 



775 



combustion chamber. This interrupts the current at the 
proper moment^ causing an electrical discharge across the 
opening in the circuity the heat from which starts combus- 
tion of the compressed gas mixture. 

An igniter plug is shown in Pig. 330. To obtain the 
necessary interruption^ one of the poles of the igniter is 
stationary, the other movable, and actuated from the out- 




FiG. 330 

IGNITER 

side by a trip. This igniter mechanism interrupts the cur- 
rent flow only at the beginning of each power stroke. The 
opposing contact points are protected by tips of platinum, 
or other heat resisting metal. 

Starting. — While small gas motors may readily be started 
by hand with a turn of the fly wheel, such a method is quite 
impracticable in large engines. An automatic system has 



776 Steam Engineering 

been incorporated in the Westinghouse engine by which 
compressed air under 100-250 pounds pressure (according 
to the size of tlie engine)^ is admitted at the proper moment 
to one of tlie cylinders whicli tlien operates^ for tlie instant^ 
as an air motor. During the succeeding rotation of the 
engine^ the other power c}dinders are carried through their 
respective cycles^ and normal combustion begins in one or 
the other upon the second or third revolution. Compressed 
air is then shut ofl^ the air valves automatically return to 
their seats, and normal combustion in the remaining cylin- 
der begins. 

SNOV^ GAS ENGINES. 

The Snow twin unit has cylinders 16 inches in diameter 
by 30 inches stroke. The cranks are set at 90 degrees apart^ 
thus giving four impulses to the shaft per revolution. The 
combustion chamber is on the side^, with the inlet valves in 
the top, and the exhaust valve in the bottom of each com- 
bustion chamber. 

The engine speed is regulated by cut-off valves which^ 
under control of the governor, shut off both the gas and 
air supply sooner or later in the suction strokes, according 
to the speed changes. The arrangement of inlet valves for 
one end of a cylinder is shown by Fig. 331. The air and 
gas pass to the mixing chamber M through separate ports, 
shown closed by the valve discs A and G, respectively. From 
the mixing chamber the mixture is admitted to the cylinder 
by the main inlet valve I at the beginning of the suction 
stroke ; at the point in the stroke determined by the gover- 
nor, the cut-off valve A G is released and allowed to close 
under the influence of its spring. The baffling ^disc B is 
adjustable so as to obtain the desired proportion of gas to 



Snow Gas Engine 



111 




Fig. 331 

sectional elevation of inlet and cut-off valves and gear. 

snow gas engine 

air, the adjustment being made by means of the knurled 
head IST, which is locked in the proper position by the set- 
screw s. The shank of the baffling disc serves also as a 



778 



Steam Engineering 



guide for the lower end of the stem of the cut-off valve. 
The valve discs A and G are connected by a short barrel D, 
the whole being a single casting. The gas valve G is pro- 
vided with a tapered seat^ and the valve-stem is adjusted 
in the block at its upper end until both discs seat simul- 
taneously. ' 




Fig. 332 
end elevation of inlet and ciut-off mechanism. snow gas 

ENGINE 

The main inlet valve I is opened and closed always at 
the beginnings and termination of the suction stroke, by the 
inlet rocker-arm (Fig. 332 ), and its stem is linked to a 
short rocker-arm E, Fig. 331, to the other end of which is 
pivoted a block arranged to slide vertically in a guide. To 
this block is hung the pivoted latch L, shown in Fig. 332, 
the end of which normally engages a dog on the block 



Snow Gas Engine 779 

which is screwed on the upper end of the stem of the cut-off 
valve. When the main inlet valve is opened, the latch L 
lifts the discs A and G of the cut-off valve. At the proper 
point of the suction stroke^ the cam C, Fig. 332^ engages a 
lug and draws the drag-link over, thereby pulling out the 
latch L and allowing the cut-off valve to drop. The drag- 
link is pivotally attached to a lug on the latch L, and its 
other end is curved around the cut-off shaft S, the upper 
leg of the bend resting on the journal box and holding the 
link in place as it slides back and forth. Before the suc- 
ceeding suction stroke begins, the cam C has turned to the 
^low^^ side and the latch Ij is thrown into engagement with 
the valve-stem dog by a small helical spring. When the 
cut-off valve drops, it is cushioned by the inverted cup E, 
Fig. 331, acting as a dash-pot, the plug F constituting the 
plunger. The cut-off cam-shaft S rotates continuously at 
one-half the crank-shaft speed, and its angular position 
with respect to that of the crank-shaft is adjusted by the 
governor through the wellrknown ^^floating'^ bevel gear. 

DU BOIS TANDEM GAS ENGINE. ' 

The Du Bois Iron Works, Du Bois, Penn., has devel- 
oped and is now building a line of single-acting tandem 
gas engines which embody several interesting features. 
Fig. 333 is a view of one of these engines, from which it 
will be evident that the design conforms to the standard 
European practice of locating the inlet valves in the top, 
the exhaust valves in the bottom, and the valve-gear shaft 
alongside of the cylinders. Another characteristic Euro- 
pean feature is the use of center-crank construction. Be- 
yond these few points, however, the design cannot be said 
to follow strictly any classified practice. 



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Fig. 333 

du bois tandem gas engine 



Du Bo is Gas Engine 



781 



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782 Steam Engineering 

The longitudinal section^ Fig. 334^ gives an excellent 
idea of the internal construction of the engine^ and shows 
clearly the unusual method employed for packing the 
piston-rod hole in the rear end of the front cylinder. 
Instead of providing a stationary packing cage, and having 
the rod slide through rings contained therein, the packing 
rings are put on the rod, like those on the piston, and they 
slide back and forth with the rod in a sleeve formed in the 
head of the front cylinder and a rearward extension of it. 
It might seem at first glance that this arrangement would 
entail an unduly long engine structure, but the fact is that 
even if stationary packing rings were mounted in a housing 
in the cylinder head, the engine could not be shortened up 
without sacrificing accessibility to the rear piston, and ease 
of dismounting the front cylinder head. Fig. 335 is a view 
of the piston rod with its packing rings and the flanged 
sleeve to which the rear piston is bolted. 

The pistons are of the trunk type, and are built with con- 
vex heads, in order to obtain the requisite strength with a 
moderate weight of metal. 

The construction of the water jackets, cylinder heads, 
connecting rod and crank case is so clearly shown by Fig. 
334 as to require no verbal description. The crank shaft, 
crank cheeks, and pin are all cast in one piece of steel ; the 
balancing weights are bolted on. 

Valves, Valve Gear and Governor, — ^^Simple, flat poppet 
valves of forged steel, with beveled seats, are used through- 
out the engine, and the need for cooling the exhaust valves 
in larger sizes ^is obviated by the use of auxiliary exhaust 
ports uncovered by the pistons at the end of the forward: 
stroke. These ports consist of a series of round holes 
through a rib connecting the water-jacket wall and the 



Du Bois Gas Engine 



783 




Fig. 336 
cross section through cylinder and valve chambers, du bois 

gas engine 



cylinder barrel, and they are drilled, instead of being cored, 
in order to obtain absolute accuracy in dimension and loca- 



784 



Steam Engineering 



tion. The inlet and exhanst valves of each cylinder are 
opened by a cani^, two push rods and four rocker arms^ as 
indicated in Fig. 336. Eollers are provided^ of course, to ; 
take the thrust of the cam and to deliver the motion of the 
rocker arms to the valve stems. 



5=K^^^e=?= 




Fig. 337 

cross section through cylinder, mixing-valve chamber and 

governor, du bois gas engine 

One mixing valve serves both cylinders, as indicated in 
Fig. 334, where the mixing valve is shown immediately 
above the rear end of the piston-rod packing sleeve. Fig. 
337 shows more of the details. The valve stem carries two 



Du Bois Gas Engine ; 785 

pistons^ the upper one controlling the air supply by vary- 
ing the space between its npper edge and the top of the 
cage^ and the lower one varying the gas supply by means 
of ports in its wall and corresponding ports in the wall of • 
its cage. The proportion of gas to air is adjusted manually 
by means of the butterfly valves in the supply passages, 
except in such cases as require variation of the mixture 
proportions, simultaneously with variation in the quantity 
of mixture admitted. For such conditions, the lever which 
raises and lowers the mixing valve is also linked to the 
butterfly valves, the linkage being adjusted so that the mix- 
ture is made richer as the load decreases (and the com- 
pression is reduced), and poorer as the load increases. This 
automatic mixture control is not necessary except when run- 
ning on very lean gases. The mechanism is adjusted usu- 
ally to give the best mixture proportions at full rated load, 
but a wide range of adjustment is practicable. 

The governor is of the flyball type, but differs essentially 
from the common construction, as Fig. 337 clearly shows. 
The spindle is driven through spiral gears from the cam 
shaft, and the balls and sliding member are inclosed in a 
stationary housing, as shown in Fig. 337. The governor 
gears are located between the forward cam and the main 
shaft; consequently, the angular velocity of the governor 
is not disturbed or made irregular by the tensional yield- 
ing of the cam shaft to the stresses imposed by the cams 
and valve mechanism. The cam shaft is driven from the 
crank shaft through spiral gears running in an oil bath. 

Ignition. — Igniters of the mechanical make-and-break 
class are used. The reciprocating mechanism which trips 
each igniter is driven by an eccentric on the cam shaft, as 
shown by Fig. 338. The individual igniter is timed by 



786 



Steam Engineering 




Fig. 338 
du bois igniter mechanism 



means of the vertical handle near the cylinder; this raises 
or lowers the horizontal finger with the bent end which 
trips the igniter, and thereby alters the point of ignition. 



Du Bois Gas Engine 1?>1 

The reach rod leading from the igniter mechanism to the 
left extends to the other igniter^ and adjustment of this rod 
to the right or left retards or advances the timing of both 
igniters simnltaneonsly. The levers to which the ends of 
this rod are pivoted are fastened to the ends of sleeves 
which are eccentric to the rocker studs^, and the igniter 
rockers are mounted on these sleeves; turning the sleeves 
on the studs alters the relation between the rockers and the 
igniter triggers and thereby changes the timing. A handle 
at the middle of the reach rod serves for manipulating it, 
and a clamp holds it wherever it is set. 

The engine is arranged so as to be oiled by a central 
gravity-feed system. Since the piston trunks are more 
than full-stroke lengthy they always cover the oil holes 
in the cylinder walls ; timed lubrication is therefore 
unnecessary. 

The engine is equipped with a valve in the head of the 
rear cylinder for starting with compressed air^ and the 
valve disc is located at the inner face of the cylinder head, 
so that when it is closed no pocket is formed in the com- 
bustion-chamber wall. This construction is shown in Fig. 
334. The indicator openings are provided with similar 
valves, as shown in Pig. 336. This drawing also shows 
the unusual feature of a water- jacketed exhaust pipe with 
which every Du Bois engine is equipped. Another unusual 
feature, although not original on this engine, is the injec- 
tion of cooling water into the exhaust pipe ; this cools the 
exhaust gases so suddenly that a muffler is not required. 
The water jacket around the exhaust pipe is chiefly for the 
purpose of obviating the exposure of dangerously hot sur- 
faces where attendants are likely to come in contact with 
them, although the water jacket also cools the exhaust gases 
considerably. 



788 



Steam Engineering 



The compression pressure is about 140 pounds absolute 
for natural gas^ and 180 pounds for producer gas, and the 
engine can be changed from the one to the other compres- 
sion in a few minutes. 



THE TOWER GAS ENGINE. 



Fig. 339 shows a view of the Tower heavy duty gas 
engine built by the Tower Engineering Company, Buffalo, 




Fig. 331) 

200 H. p. TOWEK GAS ENGINE 



N". Y. This engine is designed for using producer gas, 
and has some very pronounced features embodying the best 
practice and the most recent development in gas engine 
design. 



Tower Gas Engine 789 

The engine is of the three cylinder, vertical, single acting 
type operating on the four stroke-cycle principle. It is 
rated at 200 h. p. upon producer gas of approximately 135 
b. t. n. per cubic foot measured under standard conditions 
of 62° Fahr. temperature and 30 in. mercury pressure. 
The cylinders are each 161^2 i^i- diameter and the stroke 
is 18 inches. The area of the piston is 213.8 sq. in., the 
piston displacement is 3850 cu. in. The piston speed under 
normal operation of 257 r. p. m. is 771 feet per minute. 
The mean effective pressure in each cylinder as calculated 
from the above data is 53 pounds per sq. in. of piston area. 

The height of the engine is 121/2 feet, the length 14 1/6 
feet, the width 8^/2 feet, the floor space occupied is 120 sq. 
ft. 

The weight of the complete engine with its fittings is 
61,000 pounds which gives a weight of metal of 305 pounds 
per horse power. Each of the two fly wheels is seven feet 
in diameter and weighs 10,000 pounds. The peripheral 
speed of the wheels is 5,600 feet per minute which is far 
too low to give any cause for fly wheel explosions. Provi- 
sion is made for belting off one fly wheel if necessary, 
and for barring the engine over, during times of inspection 
from the other, by means of holes drilled in the face of the 
fly wheel. 

The crank shaft is of forged open hearth steel with high 
ultimate, and elastic limits, combined with reasonable ductil- 
ity to suit the conditions of service. The matter of crank 
shafts for vertical three cylinder engines has received con- 
siderable study of late, in view of the fact that there have 
been several breakages of late, in engines of supposedly 
good design. The pressures exerted on the crank at the 
time of the explosion are very great and, due to the rotation 



790 Steam Engineering 

of the crank shaft, the stresses are reversed from tension 
to compression so that if any defects or initial stresses are 
in the material, there is great liability to ruptnre dne to 
^^fatigne^^ or crystallization of the metal. The use of the 
best material, of good proportions, and large bearing sur- 
faces, easy to adjust and keep in correct alignment is the 
solution of the crank shaft problem. The two end crank 
shaft bearings are each 20 in. long and the two center 
bearings are each 14 in. long, with wedge take-up adjust- 
ments. The diameter of the crank shaft is 8 in., that of 
the crank pin bearings is SVo iii^ with a length of 7% in. 
The piston pin has a diameter of Si/o in., and the length 
of the bearing surface is 8 in. The oil reservoir supplies 
a sight feed indicating distributer in full view of the 
engineer. There are separate oil feeds piped from this dis- 
tributer to each of the bearings, and the engineer can easily 
adjust the flow to each bearing, and with a glance of his 
eye observe whether oil is going to every bearing or not. 
The feeding device starts and stops with the engine, the oil 
is collected in the pit of the crank case, passes through the 
filter, and is pumped to the reservoir with little waste. 

The cylinder heads contain the *nlet and exhaust valves of 
the poppet type; the latter is water cooled. The valves 
themselves are placed in cages which may be readily re- 
moved from the cylinder heads. The construction is such 
that neither valve can fall into the cylinder — a very wise 
precaution, as engines have been badly damaged by having 
an inlet valve drop into a cylinder. 

The valves are operated by eccentrics which are encased, 
and dip into a bath of oil. The entire eccentric shaft can 
be exposed for inspection by lifting the cover of the case. 

The governor case, as shown to the right under the end of 
the eccentric case in the illustration, encloses two flv-balls 



Tower Gas Engine 791 

immersed in oil^ rnnning at engine speed. The cover to 
the case can be removed for eas]^ inspection. Means are 
provided for changing the speed of the engine^ while rnn- 
ning^ by turning a knnrled adjusting nut. Connections are 
made to the governor valve by two reach rods; one to con- 
trol the gas^ and one to control the air supply. 

The governor valve^ for controlling the quality of the 
mixture^ and the compression of the engine^ is multiported 
and operates on ball bearings to insure minimum friction 
and sensitiveness. An indicator is provided to show, at all 
times^ the position of gas and air ports at all conditions of 
load. The adjustment provided on the reach rods and 
governor^ allows of the variation of air and gas separately^ 
or the adjustment of both simultaneously^ while engine is 
operating. 

The special feature of ignition is important. Two spark 
plugs are used in a plate, and by throwing a lever either 
plug may be thrown into service. 

A defective plug may thus be removed without losing a 
power stroke. An adjustable timing device, allows the tim- 
ing of each cylinder separately, or advancing and retarding 
the spark in all the cylinders at the same time. 

No batteries are used. The cylinder, cylinder head, 
exhaust valve and exhaust manifold are water cooled. 
Water is piped to each cylinder independently, and connec- 
tion is made externally from cylinder, to cylinder head. 
The water from the cylinder head is discharged into an 
open funnel so that the engineer can see at a glance that 
each cylinder is getting its proper share of cooling water. 
IThis is an important matter to consider as practice has 
ishown that cylinders heat differently, and trouble due to 
one hot cylinder may seriously injure the engine. 



792 Steam Engineering 

The starting of the engine is effected by compressed air. 
The auxiliary apparatus consists of two air storage tanks, 
a two cylinder air compressor, and a 4 horse power gasoline 
engine. 

THE KEEVES GAS ENGINE. 

Figures 340 and 341 show views of the Eeeves gas engine 
built by the Eeeves Engineering Co., Mt. Vernon Ohio. 




Fig. 340 
reeves thkee-cylinder gas engine 

This engine is designed to be operated on natural or pro- 
ducer gas, and can also be operated on gasoline if necessary. 

As will be noted by the illustrations these engines are of 
the vertical, multiple cylinder single acting type. 

The crank shafts and connecting rods on this engine are 
forged without welds from open hearth steel. Crank pin 



Reeves Gas Engine 



793 



bearings are of marine type^ and cast from phosphor bronze ; 
the adjustment of wear on these bearings being made by a 
special system of liners^ each one consisting of a number 
of sheets of brass, each being 0.003 of an inch in thick- 
ness and a number made into a unit constitute a liner. In 




Fig. 341 
sectional view of the reeves gas engine 



making an adjustment the removal of one sheet on each 
side gives equal adjustment all over the bearing. The pin 
is made from tool steel, hardened and ground to exact size. 
Pistons are of special hard gray iron, and are unusually 
long affording a liberal wearing surface. By referring to 



ii. 



794 Steam Engineering 

Pig. 341 the extreme length of the piston will be apparent. 
It will also be noted that the packing ring system consists 
of five narrow rings^ four at top for holding compression 
and one ring at the bottom which acts as an oil retainer, 
making lasting compression possible. 

The cylinder head has no offset firing chambers and the 
surface exposed to heat is thereby reduced to a minimum, 
wdiich together with the high compression gives low fuel 
consumption. To protect the gasket between the cylinder 
and the cylinder head from the firing of the charge^ the 
cylinder head is fitted with a male flange which projects 
and makes a close fit in to a corresponding counterbore in 
the cylinder. The valve stem guides on both intake and 
exhaust are made from, close grained cast iron bushings in- 
serted in the cylinder head. 

The cylinder head is thoroughly water jacketed^ and has 
a system for injecting cooling water directly around the 
exhaust valve seat. 

Cylinders are cast from semi-steely the flange for bolting 
same to housing being set three inches from end of cylinder. 
The extension below this flange is a slip flt to correspond 
to bore in housing; this centralizes the cylinder on the bed 
and also adds to the rigidity. They are iDolted (at the bot- 
tom) direct to the housings^ which consruction allows for 
contraction and expansion without throwing cylinder out 
of true. 

The governor is the throttling type^ the engine taking 
impulses regularly^ each impulse being graduated by gover- 
nor according to load the engine is carrying. The engine 
is fitted with a patent proportional throttle valve^, which 
gives a constant proportion of air and fuel under all loads. 

Either jump sparky or make and break ignition is fitted, 
according to the charcter of work or fuel on which engine 



Reeves Gas Engine 795 

is to be operated. For natural gas^ or gasoline the jump 
spark is undoubtedly the best^ but for producer gas a 
mechanically operated system of make and break spark is 
used. 

The timer is arranged so that the firing point can be 
changed while the engine is in motion. 

The spark plag is located directly underneath the inlet 
valve. 

Splash lubrication has been abandoned^ and its place is 
taken by an individual oiler on each bearing. All drip oil 
is collected in the base of the engine and drawn off through 
a drain pipe in the back. All lubrication devices are ac- 
cessible on outside for oiling while the engine is in oper- 
ation. Each cylinder has two sight feed lubricators, located 
on opposite sides of cylinder, 

THE GASOLINE ENGHSTE. 

The principles governing the action of the gasoline engine 
are essentially the same as those of the gas engine. In 
fact the term, ^^gas engine^^ applies equally well to gasoline 
and oil engines, and there is very little difference in their 
action. An engine using gas may be easily changed to use 
gasoline, or a gasoline engine may, by a few simple changes, 
be fitted to use natural, or artificial gas. The principal dif- 
ference between the gas engine proper, and those engines 
such as gasoline, oil, etc., that use a liquid fuel is, that with 
the latter the gas is generated within the engine itself while 
in operation, whereas with the former the gas is supplied 
from outside sources. In early gas engine practice a gas- 
oline or oil vapor gas was made by passing air in close prox- 
imity to a large surface of the liquid fuel. The air was 
thus saturated with the vapor of the gasoline or oil, and be- 



796 



Steam Engineering 



came a vapor gas similar to artificial or natural gas. This 
vapor gas was piped to the engine and mixed with air in 
proper proportion to secure the quickest and best com- 
bustion. This principle of mixing is used now with natu- 
ral, artificial and producer gas. The next development in 
the use of liquid fuel was the mixer or carbureter by which 
a minute quantity of the gasoline or oil is measured and 
supplied with each charge of air entering the engine cylin- 




FiG. 342 



der. With the stationary^ single cylinder^ industrial en- 
gines in common use the device for measuring the liquid 
fuel is called a mixer^ and is usually made a part of the 
engine. A gasoline or fuel pump and constant level over- 
flow cup is provided so that the gasoline tank may be located 
outside of the building in compliance with insurance reg- 
ulations about the storage of gasoline. For multiple cylin- 






The Gasoline Engine 797 



der^ and lighter engines the measuring device is called 
a carbureter, and is generally an accessory to the engine. 

Fig. 342 shows the principle of the constant level overflow 
Mixer System commonly employed in the single cylinder 
stationary engine. A is the constant level overflow cup 
showing how the gasoline or liquid fuel rises in the spray 
nozzle, F, to the same level maintained in the cup. B is 
the pipe from the gasoline pump, and C is the overflow pipe 
that leads the surplus gasoline back to the tank which, as 
stated, may be outside the building if so required. D is 
the gasoline regulator^ E the air regulator, F the spray 
nozzle and G the short passage to the inlet valve of the 
engine. At a given speed the engine draws in a certain 
amount of air by the regulator, E. The air rushing past 
spray nozzle, F, draws a small quantity of gasoline, meas- 
ured by regulator, D, from the spray nozzle, and carries it 
into the cylinder of the engine. The natural heat in th^ 
air supply, assisted by the heat of the cylinder, turns the gas- 
oline spray into a gas that burns like a flash or "explodes'' 
when compressed and ignited by the engine, provided of 
course that the right proportion of air and gasoline has 
been obtained. This is easily known by adjusting the fuel 
and air regulators, and observing the action of the engine, 
especially under load. The greatest amount of air with the 
least amount of gasoline for the strongest pull at a given 
speed will be the correct position for the regulators. For 
easy starting the air regulator should be closed a little, then 
opened again when the engine gets up speed. 

Fig. 343 is an illustration of a 1908 accessory carbureter, 
such as is commonly used on multiple cylinder and light 
motors, although it is applicable to any type of engine. A 
float, M, controlling a valve, 0, takes tlie place of pump and 



798 



Steam Engineering 



overflow system shown in Fig. 342, maintaining a constant 
level of the fuel in the spray nozzle, L. The float chamber 
is placed around the spray nozzle so that in traction or 
marine work, involving various angles and positions of the 
machine, there will be no variation of the fuel level in the 
spray nozzle. The fuel tank is usually placed above the 




Fig. 343 

carbureter, and connected by pipe P to float valve 0. The 
liquid fuel is thus fed to the float chamber by gravity. By 
using a light air pressure in the tank it may be placed 
helow the carbureter but this is not often done. The mixer 
as shown in Fig. 342 is designed for a given engine speed. 
If the engine speed is changed the air and gasoline regu- 
lators must also be changed to get the best results. The 



IE 

r2 



The Gasoline Engine 



799 



carbureter is generally designed to automatically adjust 
itself to a considerable range of engine speed. Thus in 
Fig. 343 the air for starting^ and slow speed enters at I. 
As the engine speed increases the compensating valve, G, 
opens, more air is admitted and the syphon force exerted 
on the spray nozzle, L, is kept in fairly accurate proportion 
to the requirements of the engine. 




Fig. 344 

K is a butterfly throttle valve for governing either auto- 
matically, or positively the amount of mixture admitted to 
the engine, and thus controlling the speed and power. Some 
makers connect the needle valve. A, to the throttle lever, E, 
in such a way that on full open throttle the needle valve is 
given additional opening. Other designs like the one illus- 
trated in Fig. 343 depend entirely on the compensating 
valve for the proportion of liquid fuel and air, covering the 
range of speed and power required of the engine. Aside 



800 Steam Engineering 

from the differences in regulation and control, tlie essential 
principles of the overflow^ and float feed systems are prac- 
tically the same. 

Fig. 344: illustrates the principle of the generator or mix- 
ing valve^ a very common method of measuring the liquid 
fuel for making each charge of gas for a gas engine. The 
liquid fuel (generally from a tank higher than the valve) 
is supplied to the fuel regulator^ D. When the intake 
stroke of the engine draws air through the valve a small 
quantity of gasoline or fuel oil, measured by regulator, D, 
is drawn from the drilled opening to the valve seat, G. 
When not in action the valve is held to its seat by a light 
tension spring, thus preventing the continued flow of the 
liquid fuel. This type of mixer or measuring device is 
especially well suited to two port two cycle engines, but has 
been successfully employed by large numbers of four cycle 
engines as well. E is a regulator for the stroke of the valve. 
F is a butterfly valve for controlling the amount of mixture 
admitted and the speed and power of the engine. 

Where insurance regulations or other considerations 
make it desirable to dispense with a considerable gravity 
head of fuel, the pump and overflow systems may be at- 
tached as shown in the drawing, Fig. 344. A is the over- 
flow cup showing the small quantity of head fuel supply. 
B is the pipe from the gasoline pump, and C the pipe lead- 
ing the overflow back to the tank. 

Owing to the pulsations of the valve on some types of 
engines a small amount of vapor is blown back from the 
valve with each stroke. A piece of pipe, 8 or 10 inches 
long, to be attached as indicated by H will effect quite a 
saving of gasoline or fuel oil. 

These illustrations show the principles of the various 
devices now in general use, for making gas out of gasoline. 



The Gasoline Engine 801 

kerosene or other liquid fuel. It must be kept in mind that 
they are chiefly measuring devices, and depend on the heat 
of the incoming air and the heat of the cylinder for the 
vaporization or gasification of the liquid measured for each 
charge. The lighter and more volatile the liquid fuel the 
better the vaporization. This is the reason gasoline is so 
generally used. The complete vaporization of the heavier 
oils and spirits such as kerosene and alcohol requires special 
attention for equally successful results. Even gasoline in 
cold weather needs hot air for the first few charges in 
starting. Some makers of engines provide a generating 
cup to hold a small amount of gasoline for heating the 
intake pipe for easy starting in cold weather. 

The higher the speed of the engine the less time there 
is for the thorough gasification of the measured liquid for 
each charge. The heat of the cylinder has less effect. The 
use of multiple cylinders has brought greatly increased 
practical speeds. These f acts^ together with the very desir- 
able purpose of serving each cylinder of an engine with 
an equal quantity of an equally carbureted mixture^ seems 
likely to bring further improvements in gas generating 
devices for liquid fuel. The present practice is to put the 
measuring mixer, carbureter or generator valve, as the 
case may be, as close to the cylinder intake valves as possi- 
ble, and depend principally on the heat of the cylinders for 
completing the gasification. A complete gasification of the 
charge before it reaches the cylinders would certainly add 
to the fuel economy, smoothness and reliability of action 
in high speed multiple cylinder engines, if it can be accom- 
plished in a practical way, and without possible ignition of 
the mixture in the carbureter and intake manifold. 



802 Steam Engineering 

LUBRICATION OF GAS ENGINES 

Engines which are air cooled require more lubrication in 
the cylinders^ as well as a heavier oil because the tempera- 
ture of the metal is invariably higher^ than where the water 
cooled system is in use. 

An oil suitable for this purpose must have three charac- 
teristic points^ i. e., a good body, low in carbon^ and lastly 
it must have a very high fire test. That is, the temperature 
at which the vapor coming from the oil would ignite should 
not be lower than 500 to 600 degrees. 

Any lubricant leaving a large amount of carbon or resi- 
due should be carefully avoided. 

For the crank and crankshaft bearings^ the same grade 
of lubricant as is used for the cylinder gives the best re- 
sults^ and the amount should be three to four drops per 
minute with the gravity system and a proportionately small 
amount with the force feed system. 

This method of lubrication is now being adopted on a 
large number of gas engines because of its reliability. A 
tank holding a quantity of oil is located at some convenient 
point on the engine. A small force pump is worked from 
the crank, or cam shaft as the case may be^, and forces the 
oil through brass or copper tubes directly to the bearings 
and by means of check valves located at the pump and also 
near the sight feed a pressure of several pounds to the 
equare inch is obtained and each drop of oil is assured of 
reaching the proper place. This S3^stem requires practically 
no attention other than an occasional refilling of the tanks. 

Where grease cups are used the caps or plungers should 
be screwed down at least two turns each hour. If a small 
quantity of graphite^ about one tablespoonful to one pound 
of grease is used, one full turn of the cap or plunger each 



Lubrication of Gas Engines 803 

hour will be sufficient. The graphite and grease should be 
thoroughly mixed before filling the cup. 

The fact that the lubricators are feeding is not a sign 
that the oil is reaching the proper place. Be sure the ducts 
are open and the lubricant goes to the bearing. 

Where the splash S3^stem of lubrication is used the oil 
holder or base should ha carefully cleaned before each fill- 
ing. Wipe the inside of the holder with waste or a piece 
of cloth^ being careful to remove all the particles of grit 
and sediment which will collect on the sides and bottom. 

Cylinder Lubrication. — In cylinder lubrication extreme 
caution should be exercised. Just enough oil should be used 
to thoroughly lubricate the piston and no more. An excess 
will be burned by the high heat^ and will form carbon on 
the rings^ cylinder walls and piston. This carbon will, in 
a short time, become heated causing pre-ignition and in a 
four cycle engine frequent regrinding of the valves will be 
necessary. The piston rings will also stick, causing them 
to wear uneven, and thereby much of the compression will 
be lost, as well as a large amount of the power which should 
be delivered. 

From eight to ten drops of oil per minute should be 
delivered to the cylinder, where common cups or in other 
words where the gravity system is used. With force feed 
this amount may be cut to five or six drops a minute, as 
they are much larger. An excess of oil in the cylinder 
will make itself known by the smoke from the exhaust pipe. 

QUESTIONS AND ANSV^ERS. 

508. In what respect does the gas engine differ from tne 
steam engine structurally? 

Ans. It is a much more ponderous machine than a steam 



804 Steam Engineering 

engine of equal output, and usually requires a much heavier 
crank shaft. 

509. Why should this be? 

A71S. Because the ordinary four-stroke-cycle, gas engine 
has only one working stroke in four, and requires four 
times as much cylinder area for a given amount of work, 
as would a steam engine for the same work. 

510. Define the difference between a single acting four 
stroke cycle and a double acting or two stroke cycle ga- 
engine in their operation. 

Ans. In the four stroke engine two revolutions of the 
crank are required for one cycle. In the double acting or 
two stroke, the cycle is completed in one revolution of the 
crank. 

511. Why are gas engine crank shafts made larger in 
proportion than those of steam engines? 

Ans. In order that they may withstand the increased 
torsional strains. 

512. What causes the pressure behind the piston of tho 
gas engine? 

Ans, The combustion within the cylinder of a charge 
of gas and air properly mixed to form an explosive, and 
admitted at the proper moment. 

513. When is this proper moment? 

Ans. When the piston is at the end of its instroke 
ready to start outward. 

514. Define the stages of a four cycle engine. 

Ans. First, induction; during an out stroke of the 
piston, air and gas are drawn into the cylinder in the 
proper proportions. Second, compression; on the return 
stroke the piston compresses this combustible mixture 
into the clearance space. Third, explosion ; ignition of the 



Questions and Answers 805 

compressed charge causes a rapid rise of pressure and sub- 
sequent expansion of products. Fourth, expulsion ; the 
expanded gases are expelled by the returning piston. 

515. Define the stages of a two cycle gas engine. 

Ans. First, compression of the charge. Second, igni- 
tion, explosion, and expansion, and at the end of the 
stroke the expanded products are expelled, and the cylinder 
filled by another charge of air and gas under pressure. 

516. How many compression chambers are needed for 
the two cycle gas engine? 

Ans. Two; for the reason that this type of gas engine 
requires two cylinders, either side by side, or tandem, and 
the charge of gas and air is being received in one cylinder, 
while the previous charge in the other cylinder is being 
compressed preparatory for explosion. 

517. How is the usefulness of the gas engine as a prime 
mover made apparent? 

Ans. By the fact that a suitable power gas may now be 
produced from almost any kind of commercial fuel. 

518. What are the relative volumes of gas and air re- 
quired for combustion in a gas engine ? 

Ans. This depends upon the kind of gas. Natural gas 
requires 10 to 12 cu. ft. of air per cubic feet of gas, while 
producer gas requires equal volumes of gas and air. 

519. Is blast furnace gas suitable for fuel gas? 

Ans. Yes, because it is slow burning, thus permitting 
high compression. 

520. To what pressures may it be compressed? 
Ans. 160 to 200 lbs. per sq, in. 

521. Is there as much heat in a given volume of blast 
furnace gas as in the same volume of natural gas ? 

Ans. No, there is about 40 per cent less. 



806 Steam Engineering 

522. How is the charge of gas and air drawn into the 
cylinder of a gas engine ? 

Ans. By the suction of the piston. 

523. What precaution should be observed regarding 
the admission of the air and gas? 

Ans. The air should be pure and free from dust, and 
the gas should not contain tarry matters if it can be 
avoided. 

524. How are the induction valves usually set? 

Ans. So that the first portion of the charge is air only, 
then air and gas, and finally air with a small quantity of 
gas. 

525. How is the air valve controlling the entry of the 
entire charge adjusted? 

Ans. It is set to open well in advance of the inner dead 
center of the engine, and is kept from closing until after 
the outer dead center. 

526. Why is this valve so set? 

Ans. In order that the full effect of the momentum 
imparted to entering gases at the highest rate of piston 
speed may be utilized. 

527. Upon what does the allowable compression pres- 
sure depend? 

Ans. Upon the relative proportions of hydro-carbon 
gases, and hydrogen contained in the mixture. 

528. What per cent of hydrogen is considered within 
the limits of safety ? 

Ans. Not over 7 per cent. 

529. What are the usual compression pressures carried 
with blast furnace gas ? 

Ans. 200 lbs. per sq. in. 

530. What pressure may be safely carried when pro- 
ducer gas is used ? 



Questions and Answers 807 

Ans, From 150 to 200 lbs. per sq. in. 

531. If illuminating gas is nsed^ what is the maximnm 
safe pressure? 

Ans. 120 lbs. per sq. in. 

532. How is the cylinder cooled and cleaned? 

Ans, By the injection of water or cold air through 
the clearance spaces^ and valve ports during the charging 
stroke;, or by pressure during compression. 

533. What other methods are available for cooling the 
cylinder and piston rod ? 

Ans. By means of a water jacket that surrounds the 
cylinder. The piston rod may be hollow and water cir- 
culated through it. 

534. How is the charge of gas and air ignited? 

Ans. Formerly by hot tubes of porcelain or hecnum, 
which are still used to some extent, but at the present day 
electrical ignition devices are used principally. 

535. What kind of electrical devices are used for this 
purpose ? 

Ans. Primary batteries, storage batteries, and magneto 
machines, or the current may be taken from the lighting, 
or power circuit. 

536. How many types of primary batteries are in com- 
mon use? 

Ans. Two — Dry and wet batteries. 

537. What are the elements commonly used in the wet 
battery ? 

Ans. Carbon and zinc immersed in a jar or cell con- 
taining a solution of sal ammoniac, or sulphate of copper. 

538. Describe the copper oxide battery. 

Ans. It consists of a plate of copper oxide, and a zinc 
plate, both being immersed in a solution of caustic potash. 



808 Steam Engineering 

539. What is the usnal voltage of these cells? 

Ans, From 1 to 2 volts per cell. 

e540. Describe in brief the construction of the storage 
i^ell? 

Ans. It consists of gridded frames of lead^ part of which 
-^vre filled with red lead for the positive plates, and those for 
the negative plates are filled with litharge, all being im- 
mersed in a solution of 6 parts of water to 1 part of sul- 
phuric acid. 

541. How is a dry battery made? 

Ans, A round zinc case forms one of the elements, and 
a piece of carbon in the center of the case forms the other 
element. 

542. Are there any other ingredients? 

Ans. Yes — A mixture of powdered manganese, carbon, 
and flour is packed around the carbon, while the rest of the 
can is filled with a plaster mixture of oxide of zinc and 
flour, and the whole is soaked in a solution of sal ammo- 
niac and zinc chloride. 

543. In what manner does the electric current ignite 
the charge of gas in the cylinder? 

Ans. By means of the jump spark caused by alternately 
making and breaking the circuit. 

544. What is one of the most important features con- 
nected with ignition? 

Ans, To see that ignition occurs at the proper moment. 

545. At what point in the stroke of the piston should 
ignition occur? 

Ans. This depends upon the quality of the gas used. 
With the maximum allowable percentage of hydrogen, igni- 
tion should not occur until after the piston has passed the 
inner dead center. Otherwise the result will be violent 
shocks, and strains upon the working parts. 



Questions and Ansiuers 809 

546. Do high initial explosions create the most powerful 
efforts behind the piston? 

Ans, They do not. 

547. What are the nsnal terminal pi^essnres for gas 
engines ? 

Ans. 25 to 30 lbs. above atmospheric pressure. 

548. How is the horse power of a gas engine calculated? 

Ans, Usuallj^ from the sam.e formula used in connec- 
tion with the steam engine^ and the computation is based 
upon the mean effective pressure developed at each ex- 
plosion. 

549. What percentage of the total calorific value of 
the coal is usually converted into useful work ^yith the 
steam engine? 

Ans. Prom 5 to 10 per cent. 

550. What percentage of the energy contained in the 
fuel is it possible to utilize with a modern gas-driven unit? 

Ans. From 16 to 20 per cent. 

551. How many type of apparatus are in use for the 
production of gaa for power? 

Ans. Three: the suction producer^ the steam pressure 
producer^ and the induced down draft producer. 

552. What kind of fuel must be used in the suction^ 
and steam pressure producers? 

Ans. Coke, or anthracite coal. 

553. What kind of fuel is the induced down draft pro- 
ducer adapted for? 

Ans. Bituminous coal. 

554. How may gas engine efficiency be expressed? 
Ans. In terms of heat value. 

555. Is there any difference of importance between a 
gas engine, and a gasoline or oil engine? 



810 Steam Engineering 

Ans, None of any importance. A gas engine may be 
easily converted into a gasoline engine, or vice versa. 

556. Wherein lies the principal difference between the 
two kinds of engines? 

Ans. In the gas engine proper the gas is supplied to 
the cylinder by the producer. In the gasoline engine the 
gas is generated within the cylinder^ from a charge of 
gasoline. 

557. How may the action of the gas within the cylinder 
of a gas engine be ascertained ? 

. Ans, By means of diagrams taken with an indicator. 

558. Is there any difference between a steam engine in- 
dicator^ and an indicator adapted for gas engines ? 

Ans, None in principle. The gas engine indicator is 
made somewhat stronger owing to the high pressures used. 



Modern Types of Oil Engines 

Diesel Engine. — This engine is built in both the four-cycle and 
two-cycle styles. Vaporization of the oil takes place within the 
cylinder itself, where the pressure of compression is carried suffi- 
ciently high to cause combustion of the fuel. The oil is injected 
through a valve at the top of the cylinder, which is vertical, and 
as the fuel enters the cylinder after the period of compression, 
about 600 pounds pressure per square inch is required for the 
injection. This pressure is supplied by an independent air com- 
pressor. The air necessary to support combustion is introduced 
through an air inlet valve. 

Figure 1 represents cross-sections of the working cylinder and 
head of a stationary two-stroke motor. The arrangement of slots 
in the cylinder wall, through which the exhaust gases leave the 
working cylinder, as the piston comes near the lower dead point» 




FIG. 1 

Sectional view of Diesel two -stroke cycle engine. 

810a 



810& 



Steam Engineering 



is, of course, a typical feature of two-stroke motors. .This ar- 
rangement is an undoubted advantage over four-stroke motors, 
which discharge their exhaust gases through valves. The admis- 
sion of scavenging and charging air is affected through four 
valves, arranged symmetrically in the cylinder head. 

As seen from the figure, the piston comprises at its upper end 
a cooling compartment, pistons above a given size having to be 
cooled with water or oil. Telescoping tubes through which a 
water jet in free contact with air is projected directly against the 
bottom of the piston serve to admit and carry away cooling water, 
an arrangement which avoids Siuy stuffing boxes. 

It is true that the two-stroke process entails the use of a spe- 
cial scavenging pump to discharge the exhaust gases. Four-stroke 
motors, which are more simple from a constructive point of view, 




FIG. 2 

Section of Diesel two-stroke marine engine. 



Oil Engines 



810c 



are therefore generally preferable for small and medium installa- 
tions. In connection with large units, the addition of an air 
pump, however, is of much less importance, the more so as the 
pump discharging the scavenging air works at very low pres- 
sures and accordingly under extremely favorable conditions. On 
the other hand, the reduction in weight is of paramount import- 
ance for large units, the frames, bases and flywhee|s of large 




FIG. 3 

Scheme of injection air regulation. 
Diesel Engine. 



four-stroke motors being so heavy that their transportation and 
erection entail serious difficulties. 

The two-stroke Diesel motor resembles the four-stroke type as 
far as its outside arrangement is concerned. The cylinders are 
likewise vertical; their jackets are cast of one piece with the 
frame, the working cylinders are encased and the piston is de- 
signed as crosshead. Apart from the compressed air pump, which 



BlOd 



Steam Engineering 



serves to introduce fuel oil into the cylinder and to start the en- 
gine, two-stroke motors comprise a scavenging air pump arranged, 
in accordance with local conditions, in the basement or above the 
floor. The scavenging air valves, like the other valve, are ar- 
ranged in the cylinder head. The exhaust valves are, however, 
replaced by slots in the working cylinder, and the fuel supply is 
regulated automatically in accordance with the load on the en- 
gine. All motors of this type have an attachment for changing 
speed during operation. 

Figure 2 shows a cross-section through a directly reversible 
Sulzer- Diesel marine engine, which has likewise been designed as 
two-stroke. 

In connection with large units the special regulation developed 
by the constructors would seem to deserve more than passing 
notice. These engines are thus in a position to deal with any 
sudden fluctuations in load with least variation in speed and at the 
same time can be readily connected up in parallel with any other 
prime movers of the same or any different type, such as steam 
engines, gas motors and water turbines. The working of the 
regulator will be understood by referring to Figure 3. 

The governor controls, in accordance with its adjustment, all the 
factors on which the output of the engine depends. These factors 
in the case of Diesel motors are the amount of fuel injected, the 
amount and pressure of the injection air required for vaporizing 
and injecting the fuel, as well as the variable admission of the 
vaporizer valve in accordance with the amounts of air and fuel. 
The amount of fuel, as well as the amount of pressure of the 
injection air, are adjusted for directly from the regulator. The 
regulation of the amount of injection air in the present instance 
is affected by adjusting a slide fitted into the suction conduit of 
the first stage of the injection air pump. The adjustment of the 
duration of opening of the fuel valve, on account of the valve re- 
sistance, however, requires much more energy, so that the action 
of the regulator itself would not be sufficient. A pilot valve S 
has therefore been provided, which is operated by the pressure 




FIG. 4 
Hornsby-Akroyd horizontal engine. 



Oil Engines 



810e 



from one of the stages of the injection air pump. In the present 
instance the pressure obtaining- between the first stage 1, and the 
second stage k, of the injection pump is used for this purpose, 
the conduit u serving to transmit this pressure to the pilot valve S. 
Hornsby-Akroyd Oil Engine. — In this engine, a sectional view of 
which is shown in Figure 4, the oil is first introduced in liquid 
form into the vaporizer shown at the back of the cylinder. The 
heat necessary for vaporizing the oil is supplied at starting by 
^ external lamps, but when the engine is in operation the continued 
combustion of the fuel supplies suffi'cient heat for both vaporiza- 




FIG. 5 

Hornsby-Akroyd vertical engine. 



810/ 



Steam Engineering 




13 Oil spraying- nozzle. 

14 Control lever. 

15 Hand hole cover. 

16 Crankpin brasses. 

17 Flywheel. 

18 Governor weight. 

19 Cam. 



FIG. 6 

Names of Parts. 

20 Stud carryino- governor weight. 

21 Crankcase end plate. 

22 Wrist nin bushing. 

23 Exhaust pipe flange. 

24 Speed control segment. 

25 Bracket carrying control lever. 



Oil Engines SlOg 

tion and ig-nition. Air necessary for combustion is introduced into 
the cylinder during the suction period of the cycle, this being a 
four-cycle engine. Thus the cylinder becomes charged with air 
and the vaporizer becomes filled with a spray of oil, both events 
occurring simultaneously. During the compression period the 
air in the cylinder, being forced into the vaporizer, becomes prop- 
erly mixed with the oil and an explosive mixture is formed. The 
deposit of carbon frequently found where crude oil is used does 
not enter the cylinder nor come in contact with the piston or 
piston rings, but is formed in the vaporizer cap. A rlange cover 
at the back of the cap allows the quick removal of this deposit 
periodically, usually about every sixty hours of running. In the 
vertical type of the Hornsby-Akroyd engme, shown in section in 
Fig:ure 5, the vaporizer is . placed horizontally on the side of the 
cylinder, while the air and exhaust valves are located in housings 
in the top cover. As is the case with the horizontal type, shown 
in Figure 4, the ignition of the gases in the cylinder is caused 
automatically by the heat of compression, together with the heat 
stored in the walls of the vaporizer. The method of governing 
consists in the automatic lengthening and shortening of the stroke 
of the oil supply pumps, thus giving very close regulation. 

Remington Oil Engine. — The Remington oil engine is of the 
vertical type, operating on the two-stroke cycle, the fuel being 
introduced into the combustion chamber as a liquid and gasified 
within this chamber. The engine is valveless, the gases being 
moved into and out of the cylinder through ports uncovered by 
the movement of the piston, which itself performs also the func- 
tion of a pump. The action is as follows: 

On the up-stroke of the piston a partial vacuum is created in 
the enclosed crankcase, causing air to rush in when the bottom 
of the piston uncovers the inlet port seen directly under the exhaust 
port (23), Figure 6. On the next down-stroke this air is com- 
pressed in the crankcase to about four or five pounds pressure per 
square inch. Meanwhile the mixture of oil, vapor and air al- 
ready in the cylinder is burning and expanding. When the piston 
approaches the end of its down-stroke, it uncovers the exhaust 
port (23), permitting the burnt charge to escape, until its pressure 
reaches that of the atmosphere. Directly afterward the transfer 
port on the opposite side of the cylinder is uncovered by the pis- 
ton, thereby allowing a portion of the air compressed in the crank- 
case to rush into the cylinder, where it is deflected upwards by the 
shape of the top of the piston and caused to fill the cylinder, there- 
by expelling the remainder of the burnt charge. The piston now 
starts upward, compressing the fresh charge of air into the hot 
cylinder head. Near the end of the stroke a small oil pump, 
mounted on the crankcase and controlled by the governor, injects 
the proper amount of oil through the nozzle (13), Figure 7, into 
the compressed and heated air. 

This oil is atomized in a vertical direction through a hole near 
the end of the nozzle. It is therefore vaporized and gasified be- 
fore there is a possibility of its reaching the cylinder walls. 

The spray of oil is ignited by the nickel steel plug (12), which 
is kept red hot by the explosions, because the iron walls surround- 
ing it are protected from radiation by the hood (11). By the 
burning of the oil spray in the air the pressure is gradually in- 
creased and the piston forced downward, this being the power or 
impulse stroke. Near the end of the down-stroke the exhaust 
port is again uncovered and the burnt gases discharged. 

The operations above described take place in the cylinder and 
crankcase with every revolution. Each up-stroke of the piston 
draws fresh air into the crankcase and compresses the air trans- 
ferred to the cylinder. Each down -stroke is a power stroke and 
at the same time compresses the air in the crankcase prepara- 



SlOh 



Steam Engineering 



tory to transferring- it to the cylinder by its own pressure at the 
end of the stroke. 

The same volume of air enters the cylinder under all conditions, 
and the power is regulated by modifying the stroke of the oil 
pump, which may be done by hand or automatically by the g-ov- 
ernor in the fiywheel. 




1 Cylinder head. 

2 Cylinder. 

3 Piston. 

4 Wrist pin. 

5 Connecting rod. 

6 Counter balance weights. 



FIG. 7 
Names of Parts. 

7 Main bearing cap. 

8 Crankshaft and crankpin. 

9 Crank oil hole. 

10 Crankcase. 

11 Hood on cylinder head. 

12 Igniter plug: of nickel steel. 



Oil Engines 810i 

Governor and Control. — The governor is of the centrifugal type. 
It has an L-shaped weight (18), Figure 7, pivoted to the piece 
(20) attached to the flywheel. As the engine speed increases the 
weight (18) tends to swing outward toward the nywheel rim, and 
thereby moves the arm attached to it so as to shift the cam (19) 
along the crankshaft toward tlie left in the figure. 

This cam turns with the shaft, and operates the kerosene oil 
pump. According to the position of the cam on the shaft, it will 
impart to the pump plunger a long or a short stroke, thereby in- 
jecting more or less oil into the cylinder. The long lever pivoted 
on the bracket (25) moves with the cam (19) and is used for 
controlling the engine's speed by hand. To stop the engine the 
handle (14) of the lever is pulled towards the flywheel, thereby 
interrupting the pump action altogether. 

The handle of the control lever can be fitted with an adjustable 
speed regulator when required. This device is for use on marine 
engines to enable the operator to slow down the engine. The 
speed regulator does not interfere with the action of the governor, 
but acts in conjunction with it. Whatever the speed of the 
engine may be, it is under the control of the governor. The engine 
can be controlled from the pilot house if such an arrangement 
is desirable. 

All Remington oil engines are built to operate on all grades of 
ordinary kerosene oil, while several sizes are built especially to 
operate on lower grade, semi-refined fuels, which have a variety 
of names and composition, such as fuel oil, Diesel oil, distillate, 
solar oil, gas oil, etc. 

Starting. — To start the engine, the hollow cast-iron projection 
rising from the cylinder head is heated by the kerosene torch 
furnished with the engine. When it is hot, a single charge of oil 
is injected into the cylinder by working the hand lever connected 
with the pump. The flywheel is now turned smartly backward, 
thereby compressing the charge, which ignites before the piston 
reaches the highest point, and starts the engine in the forward 
direction. 

After the engine has been started the starting torch may be 
extinguished. Ignition will take place continuously and the engine 
will not miss fire under varying loads. 

Cylinder. — The cylinder is provided with a water jacket extend- 
ing practically its full length. This insures thorough cooling of 
the piston and increases the efficiency of the lubrication. 

This water jacket is provided with two long hand hole plates on 
opposite sides of the cylinder, which may be conveniently removed 
for inspecting and removing sediment from the water jacket space. 

Ignition. — Rising from the center of the head is a hollow cast- 
iron projection, which contains the nickel steel igniter plug by 
which the oil gas is ignited. This plug is practically indestrucible 
by heat, and as it is permanently located at an exact point found 
correct by trial, it fires the charge at the right moment Under 
all conditions. 

Fuel Pump. — The fuel pump is made of bronze. The valves are 
made of bronze and are specially designed with very large areas 
and are very carefully fitted and ground. The plunger is made 
of tool steel and is hardened and ground. A bronze cup strainer 
is attached to the lower end of the pump to prevent sediment or 
foreign matter from reaching the pump valves. 

Head. — The cyHnder head is cast separately from the cylinder 
and has no water jacket about it. The packing between the head 
and cylinder is copper-asbestos. The head can be removed any 
number of times without injuring the packing. The nuts which 
hold the head are fitted to the cylinder studs so that they can be 
removed without pulling out the studs. 



Air Compression 



The compression of air always develops heat, and owing 
to the fact that compressed air always cools down to the 
temperature of the surrounding medium before it is used, 
there is a certain amount of work lost through the dissi- 
pation of this heat, the lost work being represented by the 
mechanical equivalent of the dissipated heat. In order to 
have a given volume of compressed air, at a given pressure 
at the locality where it is to be utilized for industrial pur- 
poses it is necessary to carry a higher pressure in the air 
compressor, for the reason that the heat of compression 
increases the volume of the air, and the work done in main- 
taining this excess pressure is work lost, heat energy dissi- 
pated. Another source of loss of power in air compression 
is the friction of the air in the pipes through which it is 
conveyed. Then there are dead spaces to be kept filled; 
leakages; the resistance offered by the valves; insufficient 
valve area, and various other causes of loss. The loss of the 
heat developed by compression is unavoidable. All of the 
mechanical energy that the compressor-piston exerts upon 
the air taken into the cylinder is converted into heat, and 
this heat being dissipated by radiation and conduction, its 
mechanical equivalent is lost work. It might be inferred 
from the above statement that the work, or in other words, 
the heat energy expended in running an air compressor, is 
expended upon a useless toy, merely for amusement; but 
not so, because the compressed air, when it again reaches 
thermal equilibrium with the surrounding atmosphere, ex- 
pands and does work by reason of that intrinsic energy 

811 



812 Steam Engineering 

which is exerted by it in the effort it always makes to change 
from a given temperature^ and volume^ to a state of total 
absence of heat^ and indefinite expansion. It is unnecessary 
to enlarge upon the usefulness of the air compressor, nor 
to mention the many ways in which compressed air is made 
to conduce to the welfare and comfort of man, as these 
facts are well known. A short section will be devoted to a 
discussion of the various methods employed in the utiliza- 
tion of this great natural force. 

Air compression is generally accomplished by one of the 
two methods, technically termed Isothermal, wherein the 
heat of compression is carried away as fast as it is devel- 
oped; and Adiahatic in which no heat is removed from the 
air, and a consequent rise of temperature attends the 
operation. Diagrams indicating the line of compression 
will demonstrate the resulting loss of power, due to not 
extracting the heat developed by compression. 

In the first case the compressed air will be delivered at a 
temperature corresponding to that at which it entered the 
cylinder. 

In the second, the air delivered under pressure will be 
at the high terminal temperature corresponding to that 
pressure. The first kind of compression is the theoretical 
ideal; but impossible of attainment. The second method 
of compression is the one which all pneumatic engineers 
endeavor to avoid as much as possible. The actual results 
secured in the best compressors are intermediate between 
these, but nearer to the second. Other things being equal, 
the economy of an air compressor is proportional to the 
degree in which the heat of compression is removed as 
fast as it is developed. The efficiency of the compressor, 
therefore, may be said to depend upon the effectiveness of 




Fig. 345 

the largest air compressor in the world 

Ingersoll-Sergeant Corliss Air Compressor — Compound Steam 

and Compound Air Cylinders with Semi-Tangye Frame. Steam 

Cylinders, 32 and 60 Inches; Air Cylinders, 523,4 and 32^/4 

Inches; Stroke, 72 Inches. 



814 Steam Engineering 

the cooling devices adopted^ provided that what is gained 
in this way is not elsewhere wasted in whole or in part. 
After long experience modern practice in air compressor 
design recognizes only two practical methods of removing 
the heat of compression: viz.^ jacket cooling and inter- 
cooling. These will be considered in order. 

Jacket Cooling. — Jacket cooling seeks to remove the heat 
of compression as it arises^ through the cylinder walls which 
are kept at a low temperature by cold water circulating in 
a surrounding jacket. A brief consideration of the condi- 
tions will show that jacketed barrel cooling alone can be 
only a partial and very unsatisfactory solution of the 
problem. 

With the piston at the beginning of its stroke^ the maxi- 
mum cold cylinder surface is exposed and the cylinder is 
filled with air at its lowest pressure and temperature. As 
the piston advances^ pressure and temperature increase, 
while the exposed area of cooling surface diminishes; and 
when the maximum pressure and temperature are attained 
near the end of the stroke^ there is practically none of the 
cylinder walls exposed except on the other, or intake, side 
of the piston; and if the head, too, is jacketed, it alone 
remains to exert any cooling influence. Furthermore, 
throughout the stroke only the outside layer of the air can 
be in contact with the cold surface and, air being a poor 
conductor of heat, none of the heat from the interior of the 
air volume is absorbed in the cooling water. Cylinder 
jacketing is advisable and even essential, in keeping the 
metal of the working parts at a low temperature, prevent- 
ing the coking of lubricant upon the cylinder walls and 
other evils of a hot machine. But it cannot of itself be con- 
sidered as an adequate solution of the problem of cooling 
during compression. 



r" 



o 

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H 

O 

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w 

Q 



Q 

hj 

w 

d 

M 
W 

o 
o 

w 

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w 

H 

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w 

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[ ; : I 

Ingersoll-Sergeant Corliss High Tressure Air Compressor — ■ 
Compound Steam and Four Stage Air Cylinders with Semi- 
Tangye Frame. Steam Cylinders, 20 and 40 Inches ; Air Cylin- 
ders, 3714, 201/4, 121/0 and 6 Inches; Stroke, 48 Inches; Capacity, 
2,000 Cubic Feet Per Minute. Pressure, 950 Pounds. * 



816 Steam Engineering 

However, in those constructions involving the use of a 
piston inlet tube and valve, not only the barrels but the 
heads and inlet valves, too, are chilled ; and the piston and 
tube themselves are kept relatively very cold. Thus the 
air enters through a cold passage, is in contact. on all sides 
with cold metal throughout the stroke and the maximum 
effect obtainable from jacketing alone is secured. 

Compound Compression— Inter cooling , — If at several 
points in the stroke, the piston should be stopped for a 
moment and the air, already partially compressed and 
heated, be withdrawn long enough to be cooled by some 
external means to its initial temperature, and then returned 
to the cylinder to be further compressed, it is evident that 
a fairly uniform temperature could be maintained in the 
air volume throughout the range of pressures from initial 
to terminal. The result would be in effect nearly that of 
isothermal compression. But while mechanical considera- 
tions forbid in practice such repeated starting and stopping 
of the piston, practically the same results may be secured 
by carrying on the process of compression in several cylin- 
ders, in the first of which a given low pressure is reached, 
and the air, at this pressure is discharged through a cool- 
ing device to a second cylinder, in which it is compressed 
to a still higher pressure, and discharged through another 
cooler to a third cylinder for compression to a higher pres- 
sure, the process being repeated until the required pressure 
is reached. Such a process, developed to a practical work- 
ing basis is the compound method of air compression in 
multi-stage cylinders which has become practically standard 
in air compressors for the higher pressures. 

Multi-Stage Compression, — Theoretically there is a gain 
in compound compression, regardless of the pressure, but 



Air Compression 81? 



with the lower pressures the saving is so small as to be offset 
by the greater expense and complication involved in having 
several cylinders, and the losses that are unavoidable in the 
operation of the additional parts. After extended expe- 
rience, makers of air compressors have fixed npon 70 to 100 
lbs. gauge as the maximum terminal pressure that can be 
best attained in simple cylinders, and for pressures from 
75 lbs. up they have adopted compound compression in two, 
three, and four stage machines^ the number of stages in- 
creasing witli the pressure required at terminal. At high 
altitudes,' however, with large volumes, and expensive fuel, 
this dividing line may come at a lower pressure. It is 
elastic, and depends somewhat upon the conditions. 

The cylinder ratios in a correctly designed compound air 
compressor are such that the final temperature, and the 
mean efi!ective pressures are equal in all cylinders, and all 
of the pistons are therefore equally loaded. The air com- 
pressed in the first cylinder to a pressure determined by 
the cylinder ratios is discharged through the outlet valves 
to an intercooler, where it is split up into thin streams 
passing over cold surfaces. The best practice involves a 
nest of tubes through which cold water circulates, and over, 
and between which the stream of air passes, a complete 
breaking up and subdivision of the stream being secured 
by baffle plates, and the tubes themselves. In cases of very 
high pressure the air may pass through the tubes, for struc- 
'tural reasons. A properly designed intercooler having 
sufficient cooling area for the volume of air may reduce the 
temperature of the air compressed in the first cylinder to 
at least outgoing water temperature. 

From the intercooler this air, entering the second cylinder 
cold, is compressed to a higher pressure and again 



818 



Steam Engineering 




Fig. 347 

INGERSOLL-SERGEANT CLASS "A-2" THREE STAGE STRAIGHT LINE 
STEAM DRIVEN AIR COMPRESSOR 



^ ^ Air Compression 819 

reaches a temperature about the same as that attained in 
the first cylinder. In two stage machines this air will be 
discharged directly to the receiver without further cooling, 
unless conditions are such as to render advisable the use 
of an aftercooler. In three stage machines the second 
cylinder will be known as the intermediate^ from which the 
air will pass to the second intercooler^ undergo a second 
reduction of temperature^, and enter the third cylinder for 
final compression to required pressure. 

It is seen that multi-stage compression is in effect iden- 
tical with the theoretical process already suggested, in which 
the compressing piston was stopped and the air cooled at 
intervals during the stroke.- The maximum cooling effect 
and saving is secured by making the intercoolers of ample 
proportions, and providing for the splitting-up of the air 
stream into thin sheets exposed to cooling action. 

Reduced Strains, — When compression is carried on in a 
single cylinder, the difference in the pressures at the begin- 
ning and end of stroke is the total difference between initial 
and terminal pressures, implying a great variation in 
strains on the driving mechanism and the structure of the 
machine. The greatest strains come near the end of the 
stroke, and are almost instantly relieved when the inlet 
valves open. Thus the terminal strain on a 20-inch cylin- 
der having 314 square inches area at 100 pounds pressure 
will be 31,400 pounds or nearly 16 tons. At 100 revolu- 
tions this strain is repeated 200 times per minute and de- 
mands a very rugged construction. This is a condition not 
conducive to easy operation in any but the most massively 
proportioned compressors. In compound compression, on 
the other hand, the difference between initial and terminal 
^ pressures in each cylinder is but a fraction of the total 



820 Steam Engineering 

range of pressure. The pressures^ furthermore^ are par- 
tially balanced in the several cylinders. The working 
strains on valves and other parts are consequently greatly 
diminished^ resulting in a greatly reduced wear and liability 
to breakage^ and securing free lubrication and a noticeable 
improvement in the smooth^ easy operation of the machine. 
These are all facts which contribute to continuous and satis- 
factory service^ with the least possible adjustment and 
attention.' 

As a matter of fact^ compounding the air cylinders 
transfers so much of the load from the later to the earlier 
part of the stroke that the maximum terminal strain on 
bearings is reduced fully 45 per cent over those in single 
stage compression ; in the above case^ from 3^140 ^^ton min- 
utes^^ to 1//27 — obviously a much easier proposition^ me- 
chanically. Misled by this pointy it has been common 
practice to reduce the weight and size of bearings accord- 
ingly^ the mistake being evident^ however, when it is remem- 
bered that the stoppage of circulating water in the cooler 
at once raises the load on the low pressure piston; while a 
broken or damaged outlet valve on the high pressure cylin- 
der may at any moment throw the same load on all parts 
as with a single cylinder machine. 

Improved Steam Economy. — The more equable distribu- 
tion of the load throughout the stroke in compound com- 
pression, just noted, also aids in securing a higher economy 
in steam consumption at the other end of the machine ; for 
it makes possible an earlier cut-off in the steam-cylinder and 
a consequently greater steam expansion with its attendant 
saving ; late cut-offs not being so necessary to prevent "cen- 
tering^\ Multi-stage compression with effective intercoolers 
hetween stages, also permits a higher piston speed, which is 
another factor in steam economy. 



Air Compression 



821 



Higher Volumetric Efficiency, — The air remaining in the 
clearance space at the end of the stroke must be expanded 




Fig. 348 

an illustration oe the "straight line" principle 

Showing the Arrangement of the Crosshead, Pistons, Piston 

Rods and Connecting Rods of the Class "A" Machine 

on the return stroke to atmospheric pressure before free 
air can enter through the inlet valves. The higher the pres- 



822 Steam Engineering 

sure in this clearance space^ the greater will be the volume 
of expansion and the lower the intake efficiency of the 
cylinder. 

In single stage compression^ the clearance pressure is the 
working pressure^, while in compound compression^, clear- 
ance pressure in each cylinder is terminal pressure in that 
cylinder. But in the intake cylinder this terminal pressure 
is low usually not over 25 lbs. when the final working pres- 
sure is 100 lbs. The volumetric efficiency of compound 
compression cylinders is higher for this reason^ the clear- 
ance in the low pressure cylinders only being in question. 
Another condition conducive to high volumetric efficiency 
resulting from compound compression is the fact that term- 
inal pressures^ and consequently terminal temperatures are 
lower than in single stage cylinders. 

The cylinder walls^ and more particularly the heads^ with 
the valves and ports which may be in the heads^ are there- 
fore kept much cooler^ and the entering air is not much 
heated by contact with these parts. A third element enter- 
ing into the question of capacity is the reduced leakage in 
stage* compression cylinders^ through valves^ and past pis- 
tons and rods^ with consequent loss of power. It is evident 
that the higher the pressure the greater the liability to 
leakage ; and the smaller range of partly balanced pressures 
in multi-stage cylinder reduces this loss. 

Drier Air, — One of the greatest difficulties encountered 
in air power transmission is the freezing of the moisture 
in the air^ either in the pipe line^ or at the exhaust ports of 
the air motors. One of the great advantages of the subdi- 
vision of compression into several stages lies in the oppor- 
tunity it affords for cooling the compressed air at inter- 
mediate stages to a temperature at which its moisture will 



Air Compression 823 

be precipitated. Of course, practically all of this condensa- 
tion occurs in the inter, and af tercoolers : and herein ap- 
pears the necessity for a design which will pass the air at 
low velocity with full opportunity for cooling on the water 
tubes. The moisture in suspension is withdrawn through 
the drain pipe. It is needless to say that unless some pro- 
vision is made for arresting and withdrawing the condensed 
water from the intercooler, the value of the latter as an air 
drier is lost; for the moisture is carried over into the com- 
pression cylinders, producing a condition of cutting and 
leakage in valves and rings and finally working out into the 
pipe line. Aftercoolers are in some instances as important 
as intercoolers in removing moisture. 

Better Lubrication. — If air be compressed in a* single 
cylinder from atmospheric pressure and temperature of 
60° P. to a final pressure of 100 pounds, the maximum 
temperature attained may be 484° F. This temperature 
is manifestly destructive to common lubricants, and oils of 
ordinary quality are burned into a solid, gritty, coke-like 
or gummy substance which gives the very reverse of proper 
lubrication, unless proper jacketing devices are employed 
to keep the parts cold. This deposit, moreover, collecting 
in ports and valves, may so obstruct and clog them as to 
cause leakage, and throw an added load on the compressor. 
If, however, this same volume of air be compressed in the 
first cylinder to a pressure of 25 pounds, the highest tem- 
perature which can be reached is only 233° — a heat which 
will not leave a deposit or destroy the lubricating qualities 
iof good oils such as should be used in compressor work. 
This air, passing through the intercooler, will be brought 
I back to about the original temperature of 60° and com- 
I pressed (in a two stage compressor) from 25 to 100 pounds 



824 Steam Engineering 

in the second cylinder. Here the maximnm temperature 
attained will be but little (if any) in excess of that in the 
first cylinder^ since the heat of compression is a function 
of the number of compressions^ and is almost wholly inde- 
pendent of the initial pressure. In multi-stage compressors, 
therefore, the conditions of temperature are seen to be most 
conducive to thorough lubrication of pistons and valves, 
tending toward durability and tightness of working parts, 
with long life and high efficiency of the machine. 

For pressures exceeding 100 pounds per square inch, for 
economy and safety, compounding is recommended, and 
for pressures exceeding say 400 pounds per square inch, 
multi-stage compression. 

For pressures under 100 pounds per square inch, factors 
must enter into consideration upon which local conditions 
have a bearing, viz., first cost, comparing cost of installa- 
tion of single, and two stage machines, cost of fuel, and 
horse power developed. 

Table 39 of horse powers developed under multi-stage 
compression is upon the following basis: Water- jacketed 
cylinders with temperature of air reduced to 60° F. in^he 
intercoolers. Atmosphere at 60°. Three per cent approxi- 
mately allowed for friction of piston for each cylinder. 



Table 39 

horsepower required to compress 100 cubic feet 

free air from atmosphere to various 

pressures. 



Gauge 

Pressure, 

Pounds. 



One-Stage 

Compression, 

D. H. P. 



Gauge 

Pressure, 

Pounds. 



Two- Stage 

Compression, 

D. H. P. 



Four-Stage 

Compression, 

D. H. P. 



10 


3.60 


60 


11.70 


10.80 


15 


5.03 


80 


13.70 


12.50 


20 


6.28 


100 


15.40 


14.20 


25 


7.42 


200 


21.20 


18.75 


30 


8.47 


300 


24.50 


21.80 


35 


9.42 


400 


27.70 


24.00 


40 


10.30 


500 


29.75 


25.90 


45 


11.14 


600 


31.70 


27.50 


50 


11.90 


700 


33.50 


28.90 


55 


12.67 


800 


34.90 


30.00 


60 


13.41 


900 


36.30 


31.00 


70 


14.72 


1000 


37.80 


31.80 


80 


15.94 


1200 


39.70 


33.30 


90 


17.06 


1600 


43.00 


35.65 


100 


18.15 


2000 
2500 
3000 


45.50 


37.80 
39.06 
40.15 






Table 40 




• 



CONTENTS OF CYLINDER IN CUBIC FEET FOR EACH FOOT 

IN LENGTH. 



Diameter 


Cubic 


Diameter 


Cubic 


Diameter 


Cubic 


in Inche3. 


Contents. 


in Inches. 


Contents. 


in Inches. 


Contents. 


1 


.0055 


83/4 


.4175 


21 


2.405 


1^ 


.0085 


9 


.4418 


21/ 


2.521 


1^ 


.0123 


9^/4 


.4668 


22 


2.640 


ik 


.0168 


9/ 


.4923 


22/ 


2.761 


2 


.0218 


93/4 


.5185 


23 


2.885 


2^ 


.0276 


10 


.5455 


23/ 


3.012 


2^ 


.0341 


10^ 


.5730 


24 


3.142 


2k 


.0413 


10/ 


.6013 


25 . 


3.409 


3 


.0491 


103/4 


.6303 


26 


3.687 


SVa 


.0576 


11 


.6600 


27 


3.976 


3^ 


.0668 


11/ 


.6903 


28 


4.276 


3k 


.0767 


11/ 


.7213 


29 


4.587 


4 


.0873 


113/4 


.7530 


30 


4.909 


4^ 


.0985 


12 


.7854 


31 


5.241 


4V2 


.1105 


12/ 


.8523 


32 


5.585 


4M 


.1231 


13 


.9218 


33 


5.940 


5 


.1364 


13/ 


.9940 


34 


6.305 


. 5^ 


.2503 


14 


1.069 


35 


6.681 


5/2 


.1650 


14/ 


1.147 


36 


7.069 


53/4 


.1803 


15 


1.227 


37 


7.468 


6 


.1963 


15/ 


1.310 


38 


7.886 


6^ 


.2130 


16 


1.396 


39 


8.296 


. . 6/ 


.2305 


16/ 


1.485 


40 


8.728 


.: 6M 


.2485 


17 


1.576 


41 


9.168 


[' 7 


.2673 


17/ 


1.670 


42 


9.620 


?■ 7J4 


.2868 


18 


1.767 


43 


10.084 


7/2 


.3068 


18/ 


1.867 


44 


10.560 


73/4 


.3275 


19 


1.969 


45 


11.044 


8 


.3490 


19/ 


2.074 


46 


11.540 


sy4 


.3713 


20 


2.182 


47 


12.048 


8/ 


.3940 


20/ 


2.292 


48 


12.566 















826 



Steam Engineering 



Air compression at mountain, or liigh altitudes is con- 
siderably more expensive than at sea level. This is due to 
the fact that the capacity of the compressor decreases in 
a greater ratio than does the power necessary to compress. 
At an altitude of 10,000 feet above sea level this extra 
expense amounts to over 20 per cent. Table 41 gives the^ 
efficiencies of the compressor at various altitudes. 







Table 41 






EFFICIENCIES OF 


AIR COMPRESSORS AT DIFFERENT 
ALTITUDES. 




Barometric Pressure 


^ s g 


1 




.S 




d 








<u 


>» 


t— 1 


Volumet 
ciency 
pressor 


"oU 




TS 
S 

^ 


II 


GUI 







30.00 


14.75 


100 







1.8 

3.5 

5.2 

6.9 

8.5 

10.1 

11.6 

13.1 

14.6 

16.1 

17.6 

19.1 

20.6 

22.1 

23.5 


1000 

2000 

3000 

4000 

5000 

6000 

7000 

8000 

9000 

10000 

11000 

12000 

13000 

14000 

15000 


28.88 
27.80 
26.76 
25.76 
24.79 
23.86 
22.97 
22.11 
21.29 
20.49 
19.72 
18.98 
18.27 
17.59 
16.93 


14.20 

13.67 

13.10 

12.67 

12.20 

11.73 

11.30 

10.87 

10.4G 

10.07 

9.70 

9.34 

8.98 

8.65 

8.32 


97 
93 

90 
87 
84 
81 
78 
76 
73 
70 
68 
65 
63 
60 
1 58 


3 
7 
10 
13 
16 
19 
22 
24 
27 
30 
32 
35 
37 
40 
42 



Table 42 gives the volume in cu. ft. of free air that will 
flow from circular openings, of diameter from 1/64 in. to 2 
inches, and under pressure of from 2 lbs. to 100 lbs. per 
sq. in. 



Air Compression 



827 



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bt b b if^ bo b to b 

O O O © Oi Oi ^*^ or 
or to CO 



-lOTCOtOMM 

00 i-i ox 05 CO CO 00 ax to 

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4 
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828 



Steam Engineering 






W 
Ph 

<u 

W ^ 

rj en 

PS^ O 

C 4> 

H *^ 

W o 

W ^ 



!2; u ^ 



03 <^ 



I s 






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bfl 



< ^ 

o 

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O 

c 





Cfl 




o'? 




o S 




•H ^ 




o 




PLh 




-o 




o c 




05 :3 




o 




Ph 




en 










00 o 




Ph 


w 




rt 




p 


en 

'd 


m 


^ 5=! 


in 


S ^ 


W 


^ P 


Pi; 


P-i 


Ph 




W 




o 




p 


en 


< 


3§ 


o 


p^ 


Pk 


w 




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1— 1 




w 




u 




w 


en 


p^ 


o"? 




lo 3 




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(^ 




en 




-o 








(1h 




en 




TJ 




o 5 




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o 




Ph 




en 


*o 


o; 0^ 




o-c 


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^^ 


R 


i-iKH 


p 


^.S 



rHOlOfOrHC^lOlft 



CO^.OOLO 

tH iO CO '^' rH CO t^ CO 

c^ o rH t- 00 :3; 

(MCOiOOO 



CO CO (M 
COCOCOCsj 

' tH iO tH »0 tH O C^i lO TjH 

(M 00 Ci Tfi CO CO O 
rHC0»0t-O 



rHTt<05COiHTtiCO»00 

T-l L- t- O I- 00 CO 

T-<C0^<X>O5 



T-HTt^COb-r-lOOOThiM 

tH CO lO CO <M O (N 

T-KM'-tiCOCO 



(M tH CO lO M 

'^. "^ CO '^' 00 d (m' TfH m" d d 

rHlOC0C0CO<MrHC0 
THCMC0lOb-05 



00 CO 
O-fCO 

c^oocotjhoo 

'cococo rHiocdcModd 

THiO(MiHC000lO00 
tH ca CO Tt^ CO CO 



iHt-ItHIM 



Air Compression 



829 



5 -l Ci Ol 4i». CO hO I- . 



CO to M . . • 

CO M io c;< J-i • 



t*^!"". . . . • 
b GO b 4^ io U : 



' ' ^ b b 4^ io 'k-i b ■ 

• • OOOOlOOOi' 



tOM 

bx '*>■ bo b CO io b b b b : 

• OC^OCOIOCOOTIOM. 
en lO CO CO ■ 

tob*4^coiol-ibbb; : 

OlQOCOOOt-^iJ-tOM. • 

or 00 -no • < 



i4i. lO M h-i O O O . 

o ro a« o ^ CO h-i . 



t-iOOOOO. 
^ ^ 05 4^ lO M • 
MOiC?!- 



ooooo. 

-14^IOMh^< 

c;t 00 00 10 • 



Equivalent Vol- 
ume oi Free Air 
Discharged per 
Minute. 



1 Inch. 



1^ Inch. 
VA Inch. 

2 Inch. 

2^ Inch. 

3 Inch. 

4 Inch. 

5 Inch. 

6 Inch. 

7 Inch. 

8 Inch. 

10 Inch. 
12 Inch. 
14 Inch. 



o 

m 

So 

^^ 

o^ 
Kg 

•u o 
w a 
■ o 

>i 

go 

^^ 

!X1 ^ 

S^ 

gS 
^^ 
o^ 

►^ Pd 

> 2 

«^ 

w o 
n :^ 

5 w 

i^ 
2 ^ 

o 

W 
O 



w 

CO 



830 



Steam Engineering 



As before stated there is considerable loss of pressure 
caused by friction of compressed air in its passage through 
pipes, and the resistance offered by elbows and valves. 
Table 43 gives the loss of pressure due to friction for every 
100 feet of pipe varying in diameter from 1 inch to 14 
inches, with an initial pressure of 80 lbs at the receiver. 

For the compression part only, of the stroke when com- 
pressing and delivering air from one atmosphere to a given 
gauge pressure in a single cylinder, the mean effective pres- 
sure is always lower than the mean effective pressure for 
the whole work. This is shown for both Adiabatic, and 
Isothermal compression by Table 44. 

Table 44 
mean effective pressures. 



Gauge Pressure 1 

Gauge Pressure , ^ 

Gauge Pressure J 

Gauge Pressure 4 

Gauge Pressure - • ^5 

Gauge Pressure ""^ 



10 
Gauge Pressure ^ 15 

25 
30 
35 
40 



Gauge Pressure 

Gauge Pressure 

Gauge Pressure 

Gauge Pressure 

Gauge Pressure 

Gauge Pressure 45 

Gauge Pressure 50 

Gauge Pressure 55 

Gauge Pressure oO 

Gauge Pressure 65 

Gauge Pressure 'J'O 

Gauge Pressure 'J'5 

Gauge Pressure 80 

Gauge Pressure 85 

Gauge Pressure ^ 

Gauge Pressure 95 

Gauge Pressure 100 



Adiabatic 
Compression 

.44 
.96 

1.41 

1.86 

2.26 

4.26 

5.99 

7.58 

9.05 
10.39 
11.59 
12.8 
13.95 
15.05 
15.98 
16.89 
17.88 
18.74 
19.54 
20.5 
21.22 
22. 
22.27 
23.43 



Isothermal 
Compression 

.43 
.95 

1.4 

1.84 

2.22 

4.14 

5.77 

7.2 

8.49 

9.66 
10.72 
11.7 
12.62 
13.48 
14.3 
15.05 
15.76 
16.43 
17.09 
17.7 
18.3 
18.87 
19.4 
19.92 



Table 45 will serve to show the requirements at sea level, "T 
of rock drills driven by compressed air, and Table 46 gives 
the increase of pressure required at various altitudes. The 



Air Compression 



831 



factor of mnltiplication is also given in Table 46 for the 
different attitudes and pressures. 

Table 45 

approximate amount of air required at sea level 
for specific sizes rock drills. 



Size of Cylinder 2 2 J 2 J 

Diam. of Hole Drilled.. 1-lJ l|-li 1-2 



21 



3 
lJ-3 



31 34 3^ 

lJ-3 11-3 11-3 



Air Pressure. 



Air Compression at Sea Level of one Drill — Cubic 
feet per minute of free air. 



60 
70 
80 
90 
100 



60 
70 
80 
85 
95 



65 

75 

85 

90 

100 



70 

80 

90 

95 

110 



80 

90 

100 

115 

125 



105 
115 
130 
140 



100 110 

115 125 

130 140 

140 150 

155 170 



120 
135 
150 
170 
185 



Table 46 

factors for computing requirements for drills 
at various altitudes. 




«5PH U 

O d 



FACTOR OF MUL fPLICATION 



Pressure at Drill 



60 Lbs. 



70 Lbs. 80 Lbs. 



90 Lbs. 100 Lbs. 





14.7 


1.00 


L133 


1.26 


1.40 


1.535 


500 


14.45 


1.015 


L15 


1.28 


1.425 


1.563 


1,000 


14.12 


1.03 


1.17 


1.31 


1.45 


1.59 


1,500 


13.92 


1.048 


1.19 


1.33 


1.48 


1.62 


2,000 


13.61 


1.06 


1.21 


1.35 


1.50 


1.645 


3,000 


13.10 


1.10 


1.25 


1.40 


1.55 


1.70 


4,000 


12.61 


1.131 


1.287 


1.443 


1.60 


1.755 


5,000 


12.15 


1.17 


1.33 


1.495 


1.652 


1.81 


6,000 


11.75 


1.20 


L37 


1.537 


1.705 


1.87 


7,000 


11.27 


1.24 


1.42 


1.59 


1.76 


1.935 


8,000 


10.85 


1.282 


1.465 


1.645 


1.825 


2.00 


9,000 


10.45 


1.32 


1.51 


1.70 


1.90 


2.07 


10,000 


10.10 


1.365 


1.56 


1.755 


1.968 


2.143 



Installation. — It should be the first care in installing 
an air compressor to provide it with a suitable foundation. 
The compressors are self-contained and need foundations 
only of such design and strength as will insure the com- 
pressor remaining rigidly in place. A poor foundation costs 



832 Steam Engineering 

almost as much as a good one^ and as a compressor is 
usually a permanent fixture^ it is advisable to put in a good 
foundation. 

Blue prints are usually furnished showing location and 
proper size of foundation bolts for each machine, from 
which a template can be made by which the foundation bolts 
can be accurately located. It is of great importance that 
space should be left around foundation bolts so that they 
may be left free to move. The setting of the compressor 
is rendered much easier by taking this precaution. A good 
way to do is to put a short piece of pipe around each foun- 
dation bolt, carrying it up with the foundation, thus leav- 
ing the desired space behind it. In case a concrete founda- 
tion is installed, the pipe should be full length around each 
rod. 

Setting Compressor. — After the compressor has been 
placed in position, block the compressor off the foundation 
about 1^ inch by means of iron wedges, upon which the 
compressor should set level. Then the cement should be run 
into the bolt holes, and also between the base of the com- 
pressor and foundation to insure true bearing all around. 

Pipe Connections. — The steam and exhaust pipes should 
be as free from L's as possible, and should be used only in 
so far as is demanded by expansion of pipes. All pipes 
should be thoroughly cleaned before starting the com- 
pressor, so that metal chips from cutting pipes may not be 
carried into the steam ch^st and score the valves and seats. 

Proper allowance should be made for the expansion of 
the steam pipes in connecting them up. 

A drain pipe or bleeder should be provided for live 
steam, connection being made directly above throttle valve 
and with the drain, so that the water of condensation may 



Air Compression 833 

not have to pass through the steam cylinders. If steam 
connection for the compressor is taken from the main 
steam line instead of direct from the boilers, the connec- 
tion sho.uld be taken from the top of the steam pipe, thus 
avoiding the carrjdng of condensation. 

The cocks and drains provided for both steam and air 
ends should be opened after the pump ceases operation, so 
that the water may be thoroughly drained, thereby avoiding 
any possibility of freezing. 

In connecting water pipe to jacket around the air cylin- 
der care should be exercised to allow for proper drainage of 
cooling surface and pipes. In cold weather the water 
should be drained, or breakage from freezing might occur 
in cylinder or jacket. 

In piping air discharge pipe use lead in all joints, and 
screw up tight, as air leaks are expensive. 

INGERSOLL-RAND AIR COMPRESSOR. 

Fig. 347 shows a view of an Ingersoll-Rand Class ^^A^' 
straight line air compressor. Its distinctive principle is 
the direct application of power to resistance, being in itself 
a distinct unit. This is clearly shown in Fig. 348. In the 
single stage types the heads, and barrel of the air cylinder 
are completely water jacketed, thus insuring economical 
compression. 

This is supplemented in the two stage Class ^^A-2'' types 
by a horizontal intercooler of effective design. In three 
stage modifications, high and intermediate pressure cylin- 
ders, with their valves and high pressure intercooler, are 
completely submerged in water-box coolers. 

Fig. 349 will serve to give to the student a good idea of 
the internal construction of this type of air compressors. 



834 



Steam Engineering 



each part being numbered and the designation of the parts 
given in the caption. 

The Meyer cut-off valve gear is clearly shown in the 
steam end, and the Ingersoll-Sargeant piston inlet valves 
are shown in the air cylinder, an enlarged view of which is 
presented in Fig. 350. Formerly all Class "A'' com- 
pressors, except 30-inch stroke machines, were fitted with 
A5 Air and A14 Steam Regulators, now called ''Unloader'' 
and "Eegulator/^ 




Fig. 350 
ingersoll- sergeant piston inlet valve cylindeb 

The standard governor for all Class ''A'' compressors 
is the type known as the ''Air-BalV Governor. 

Unloader and Regulator,— Th^ function of the unloader 
and regulator is to take the load off the air piston 
when the pressure reaches, the desired point, and, 
at the same instant, to throttle the supply of steam 
to a point just sufficient to keep the compressor 



QQ7 



Ingersoll-Rand Air Compressor 835 

turning over. When the pressure of air goes down 
past the limit, usually ten pounds below the running press- 
ure, the load is thrown on and the steam again admitted 
when compression is resumed in the regular wav This 
IS accomplished as follows: When the weighted "lever is 
iown the pii,es leading from the unloader to the discharge 
ralves, and to, the steam regulator cylinder (No. 155), are 
ilJed with air at receiver pressure. The result of this is 
hat the discharge valves act in the nature of check valves 
Btting the compressed air out of the cylinder, but not in 
gam, and the steam regulator valve (No. 92) is held open 
.lus admitting of the compression and discharge of the air' 
-'hen the air pressure rises above the point at which the air 
to be carried the weight will lift, resulting in the air 
which was under pressure in the pipes referred to) being 
:hausted. When this pressure is relieved the discharge 
lives throw wide open, and stay wide open, the result 
ing, of course, that the inlet valves are held shut, the 
ston has receiver pressure on both sides, and moves back 
jd forth in equilibrium. At the same instant the steam 
?ulator valve closes to a point which admits just enough 
iiam to overcome the engine friction and keep it moving 
it enough to prevent centering. The extent to which 
\} steam regulator valve closes is regulated by screwin- the 
lusting nut (No. 158), Fig. 349, one way or the other, 
len the compressor is running without a load, until ihl 
^per speed is secured. The pressure at which the com- 
jssor ceases to discharge air into the receiver mav be de^ 
mined by the weights hung on the regulator. The safety. 
Ive on the receiver is set to blow at about tm, pounds 
,YC ^he regulator pressure, and in practice sliould rarely 
never blow. See that the stop-cocks on the pipes leading 



836 Steam Engineering 

from the regulator to the discharge valves are wide open. 
The causes for the regulator not working properly, if the 
pipes are clear, are to be looked for as follows. 
See that packing is not too tight, and that the steam valve 
moves freely. See that valve (No. 146) moves freely. See 
that plunger (Ko. 142) moves freelj^, and that lever does 
not bind. An occasional cleaning out with kerosene may 
be necessary if there is any tendency to gum up, which is 
rarely the case. 

To Remove Inlet Valves. — ^Loosen the jam nut on the 
air piston rod, and screw rod out of swivel block; remove 
back head (No. 99), on air cylinder; slide air piston 
out on plank; remove piston rings; unscrew screw plugs 
(No. 107) ; remove inlet valve pins (No. 106) ; these 
are tapered and can be started out with a drift sent with 
the compressor for that purpose. When these pins are all 
out the valves can be removed, and the whole operation 
can be performed in a short time. 

The valves can then be inspected, and proper repairs 
made. If there is any deposit of dust or gum in the piston, 
it can be removed while it is out. If new inlet valves are to 
be put in, the seat should be scraped, so as to allow the 
valves to seat air-tight; but this will rarely be necessary. 
If the valve pins are worn flat where the valve has been 
striking them, put in a new set of pins when replacing the 
valve, or turn the pins around so that the valve has a true 
surface of the pin to strike against. Do not set the pins 
90 that valve will strike against a sharp corner on sam.e, 
as it tends to wear the valve very rapidly. When putting 
in valves -it is best to use new pins. 

When replacing the piston, those ends of the rings 
having the same marks should go together; thus, 1-1, 2-3 



Ingersoll-Rand Air Compressor 837 

and 3-3 go together. A piece of stout cord lapped around 
the rings and tied will hold them in place until slipped 
beyond the counterbore^ after which the cord is to be re- 
moved. 

To Set the Cut-Off Eccentric. — Different portions of 
the stroke are laid out along the cross-head slide in reference 
to each end of the stroke; the cut-off valves are screwed 
on the rod together^ and the cross-head being set at any 
desired part of the stroke the cut-off valve is moved (by 
turning the hand wheel) so that it just cuts off the port 
on the main valve. The cross-head is then moved to a 
corresponding position at the other end of the stroke, when 
the other cut-off valve should just close the port on main 
valve. If it does not, the valve stem should be lengthened 
or shortened in the eye piece, or one cut-off valve can be 
put on the stem a thread or two sooner than the other, thus 
equalizing them for both ends of the stroke. 

There is only one position where they will cut off exactly 
the same on both ends, and if varied from this the cut-ofl; 
will be different on both ends of the stroke, being greater 
relatively on one side if increasing the cut-off, and less 
relatively on the same side when diminishing the cut-off. 

In other words the cut-off valve may be arranged to close 
correctly at one half (or any other fixed part of the stroke ) 
but at one fourth cut-off, one valve will be a little ahead of 
the other, and at three-fourths cut-off the opposite end Avill 
be the other way, so that the best that can be done with this 
style of cut-off is to obtain one correct point of cut-off'; 
that may be one half, or any other desired point, but at 
all other points it will not be exactly correct. A good way 
to get the engine on its exact dead center is as follows: 
Turn the fly-wheels till the piston is wUhin an inch or so 



838 Steam Engineering 

of the end of its stroke. Scribe a fine vertical line across 
the edge of the cross-head and guides; scribe another line 
across the face of the fly- wheel, horizontally, or any con- 
venient part of the rim, guiding the scriber across the plan- 
ed edge of a board nailed rigidly in position. Now turn 
past the centre till the cross-head comes back exactly to the 
line, and scribe across the straight edge on the rim again. 
Now draw another line across the rim, exactly half way 
between the first two, and when the fly-wheel is turned to 
bring this last line even with the straight edge, the engine 
will be exactly on the dead centre. The centre at the other 
end of the stroke may be marked in the same way, after 
which you can turn to either centre instantly and without 
liability of error. 

Air Ball Governor, — This device is at the same time a 
speed regulator or governor, and a means for holding a con- 
stant air pressure in the receiver. It consists of a special 
balanced throttle valve, the spindle of which is connected 
to a fly-ball governor belted from the engine shaft. This 
throttles the steam supply when the engine speed exceeds 
the desired limit. 

At one side ,of the governor is a small air cylinder, the 
piston of which presses against a lever on which is a sliding 
weight. This cylinder is connected with the air receiver. 
The inner end of the weighted lever connects with the 
spindle of the balanced throttle through a link which 
makes the action of the small air cylinder independent of 
the fly-ball governor, so that when the pressure in the 
receiver exceeds that for which the governor is set, the 
weigtited lever is raised, and the balance throttle closed to 
a point which admits steam enough to turn the machine 
over at the speed necessary to supply a volume of air equal 
to that being drawn from the receiver. 



Ingersoll-Eand Air Compressor 839 

If from any cause the air pressure in the receiver drops, 
the weighted lever is allowed to drop, by the decrease of 
pressure in the small cylinder. This opens the throttle, 
admitting more steam to the engine. If an air pipe should 
break, or too great a demand is made upon the compressor, 
keeping the air pressure down so that the air piston does 
not work, the engine speeds up tq a point where the centrif- 
ugal governor partially closes. 

Setting Meyer Slide Valves. — Set the main eccentric, 
actuating the lower valve, so that the angle centre advance 
is somewhere near fifteen degrees, thus : 




Fig. 351 
mason pump governor 

Put the crank on either dead centre and set the main 
valve at that end so that it has about l-64th inch lead, and 
set the nuts against valve temporarily; now turn the wheels 
to the other dead centre, and see how far the port edge of 
valve is from the edge of port. Whatever this distance 
is, the valve should be moved one-half this distance along 
its stem, by loosening the nuts on one side and screwing 
up on the other. When this distance has been exactly di- 
vided the nuts should be jammed up tight, so that they 



840 



Steam Engineering 



just bear against the valve. The valve stem will then be 
of the correct length. With the crank at dead center move 
the eccentric aronnd so that the valve has 1/64 inch lead^ 
and fasten the eccentric there ; then turn the crank to the 
opposite dead center^ and note if the lead is the same — if 
not, average it as close as possible. 




Fig. 352 
mason pump governor — sectional view 

Mason Pump Governor, — Figs. 351 and 352 show the 
Mason Pump Governor which is used only on compressors 
for the Pohle air lift outfits, or in case a constant speed is 
desired irrespective of the load. 

The Mason Pump Governor attaches directly to the 
eccentric rod of the compressor, and operates a balanced 



Mason Pump Governor 841 

valve placed in the steam pipe^, thereby exactly weighing the 
amount of steam to the needs of the compressor and econo- 
mizing the same. By using the Mason Governor the com- 
pressor can be set or changed to ran any required speedy 
which will be maintained in spite of variation in load or 
steam pressure. As all the working parts of the governor 
are immersed in oil^ the wear is reduced to a minimum. 

The Mason Governor consists of a cylindrical shell or 
reservoir filled with oil or glycerine. The plunger AA 
(Fig. 352) is connected through the arm I to some re- 
ciprocating part of the pump or engine^ and works in uni- 
son with the strokes of the compressor^ thereby drawing the 
works in unison with the strokes of the compressor, thereby 
drawing the oil up through the check valves DD into the 
chambers JJ, whence it is forced alternately through the 
passages BB, through another set check valves into the pres- 
sure chamber EE. The oil then returns through the orifice 
C^ the size of which is controlled by a key inserted at N", 
into the lower chamber^ to be repumped as before. In case 
the engine works more rapidly than is intended^ the oil is 
pumped into the chamber EE faster than it can escape 
through the outlet C^ and the piston GG is forced upward, 
raising L with its weight and throttling the steam. In. 
case the compressor runs slower than is intended^ the re- 
verse action takes place^ the weight on the end of the lever 
L forces the piston GG down and more steam is let on. As 
the orifice at C can be increased or diminished by adjusting 
the screw at IST, the governor can be set to maintain any 
desired speed. The piston GG fits over the stationary 
piston forming an oil dash pot, thereby preventing fiuctua- 
tion of the governor. This dash pot is fed from pressure 
chamber E through a passage which is controlled by an 



842 Steam Engineering 

adjusting screw K^ which is set b}^ a screwdriver (after re- 
moving the cap screw T). It requires no further attention 
when 'once adjusted. 

The governor is placed on the compressor, where the 
requisite motion can be obtained for operating it, and also 
in such a way that a rod can be run from the knuckle joint 
on the top lever to the valve in the steam pipe. N'ow place 
the valve in the pipe so that the stem shall be in a direct 
line with the knuckle joint on the lever, pull out the valve 
stem to its full extent, then, with the ball on the governor 
in its lowest position, connect the valve rod with the lever. 
The governor is then read}^ to fill. To do this remove the 
plug in the top of the gauge glass, and with a good clean, 
light grade of mineral oil fill the governor about half full. 
The governor is then ready for work. 

To Start. — First start the compressor at about the de- 
sired speed, and get it working well '; then, placing the key 
in the key-hole on the side of the governor, turn to the right 
until the speed of the compressor has diminished slightly. 
Then open the throttle valve wide, and the compressor will 
be under full control of the governor. Should there be 
much jumping, or fiuctuating of the ball remove the screw 
T, insert a small screwdriver, and screw adjusting screw 
in at K until it ceases. After the governor has run a little 
while it will be found that the oil in the glass gauge has 
lowered considerably. It should then be refilled, so that the 
glass will stand about half full when the governor is at 
work. Under no circumstances should the gauge be full, 
as it will prevent the ball from coming down and opening 
the valve when the steam lowers. As there is no pressure 
upon the gauge, the governor may be refilled while in 
motion by removing the plug in the top of the gauge glass. 



Dallett Air Compressor 843 

THE DALLETT AIR COMPRESSOR. 

Fig. 353 shows a sectional elevation of the Dallett Air 
Compressor built by the Thomas H. Dallett Company of 
Philadelphia, Pa. This compressor incorporates the essen- 
tial features of having all parts requiring adjustment or 
renewals readily accessible, and employing a liberal amount 
of metal, so placed as to insure rigidity in operation. 

The frame is of the open-fork center-crank type, de- 
signed to obtain on each size of compressor a greater range 
of capacity by substituting, when desired, a cylinder of the 
next larger size than the standard to operate at 100 pounds 
pressure. 

The main bearings are lined with babbitt metal, which is 
thoroughly peened in to obviate shrinkage, and then bored 
and scraped to fit the crankshaft. The duplex-belt, duplex- 
steam and single-steam machines are supported on deep, 
rigid sub-bases, thus making the entire machine self-con- 
tained. 

The steam cylinder ajid valve gear of the steam-driven 
machines are designed to give high efficiency. All steam 
ports are short and direct, and the clearance has been re- 
duced to a minimum. A plain D balanced slide valve is 
used on the small and medium-sized machines, and the 
Meyer balanced adjustable cutoff valve in the larger ma- 
chines. To provide efficient insulation, all steam cylinders 
are lagged with mineral wool and jacketed with sheet 
steel. 

The governor of the steam-driven machine is equipped 

with a safety-stop device. The governor pulley is situated 

on the end of the shaft outside of the fly-wheel on the 

I single-steam machine, thus bringing the flywheel as clbse 

to the bearing as possible. Formerly, in the case of duplex 



844 



Steam Engineering 




Fig. 353 
sectional elevation of dallett steam driven air compressor 

compressors with compound steam cylinders^ if the ma- 
chine stopped with the high-pressure side on the dead 



Dallett Air Compressor 845 

center^ it would not start antomatically^ due to the fact that 
the high-pressure side takes steam from the line. 'This 
trouble has been overcome by using a reducing valve which 
reduces the live-steam pressure for use in the low-pressure 
cylinder. The air and steam cjdinders are tied together 
and held in position by means of an internally flanged tie 
or distance piece. 

Mechanically operated inlet valves are supplied on any 
size of compressor if desired. These valves are ground to 
gage and the valve holes lapped to size. 

The air-intake and discharge valves are special features 
of these compressors. The intake valve is of the automatic 
poppet t3^pe^ contained in a malleable-iron cage. 

ALLIS-CHALMERS AIR COMPRESSOR. 

Por single-stage air compressors^ and in the high-pressure 
cylinders of two-stage air compressors, the Allis- Chalmers 
Company, of Milwaukee, uses as a standard the arrange- 
ment of valves shown in Pig. 354. Eotary valves are used 
for the inlet, and plain, single-beat poppet valves for the 
discharge. The inlet valves are driven by an eccentric on 
the main shaft, and, by means of the wrist-plate,, they are 
given the quick opening and closing, and the slow move- 
ment when the ports are covered and the valves under 
pressure, which is characteristic of the Corliss valve-gear. 
The inlet ports are of ample size, short and direct, and the 
air is* guided into the cylinder by an easy curve, thus re- 
ducing the entering friction, and insuring the complete 
filling of the cylinder with as little loss in pressure, and at 
as nearly the outside pressure as possible. 

The discharge valves are of the drawn-steel cup type and 
open automatically when the pressure in the cylinder equals 
the discharge pressure. 



846 



Steam Engineering 



A modification of the valve-gear shown by Pig. 454 is 
illustrated in Fig. 355. In this gear the inlet valves are 
operated the same as in Fig. 354^ but the discharge valves 
are mechanically closed^ being free to open automatically, 
and positively closed by plungers operated by connections 
to a wrist-plate driven by an eccentric on the main shaft. 
The movement of the plungers of the discharge valves is 




J^iG. 354 

AIR CYLINDER WITH AUTOMATIC DISCHARGE ^ALLIS-CHALMERS AIR 

COMPRESSOR 



so timed as to positively bring. the valves to their seats just 
as the piston reaches the end of its stroke, thus avoiding 
any slip of air back by the valves and also to avoid slam- 
ming when the piston commences to return. As soon as 
the valves are closed the plungers recede, leaving the valves 
held to their seats by the discharge air pressure until that 
point in the return stroke of the piston is reached where 



Allis-Chalmers Air Compressor 



847 




Fig. 355 
aib cylinder with mechanical discharge valve — allis-chal- 
mers air compressor 



848 



Steam Engineering 



ihe pressure in the cylinder equals the discharge pressure, 
when the valves are free to open automatically. In closing, 
the air between the plunger and valve forms a cushion 
which is so adjusted, and gradually reduced that the valve 
is brought gently to its seat without noise or pounding. 

A third type of valve-gear is shown in Fig. 356. In this 
I)oth the inlet and discharge valves are of the rotary pat- 




FiG. 356 

^lE CYLINDER WITH MECHANICAL DISCHARGE VALVE- 
MEKS Alli COMPEESSOR 



-ALLIS-CHAL- 



iern, positively operated by independent eccentrics on the 
main shaft. The inlet valves are the same as described in 
the two preceding types. The discharge valves are so propor- 
tioned and adjusted as to close positively just as the piston 
reaches the end of its stroke, and to open at any predeter- 
mined maximum discharge pressure required. In addition 
lo the rotary discharge valves^ the cylinder is fitted with 



Allis-Chalmers Air Compressor 849 

auxiliary poppet valves of the steel-cup type^ which serve 
as relief valves in case the eccentric should slip; or for 
allowing the air to be discharged from the cylinder, should 
the pressure, for any cause, fall below that at which the 
main discharge valves are set to open. 

QUESTIONS AND ANSWERS. 

599. What is one of the results of compressing air? 
Ans, The development of heat. 

560. What amount of work is lost by the development 
and dissipation of this heat? 

Ans. The work represented by the mechanical equiva- 
lent of the heat .developed. 

561. Mention another cause of more or less lost work 
in air compression? 

Ans, Friction of the air in the pipes through which it 
is conveyed. 

562. By what two methods is air compression generally 
accomplished ? 

Ans, Isothermal, by which the heat of compression is 
carried away as fast as developed ; and adiabatic, by which 
no heat is removed from the air. 

563. Which of the two is the ideal method of com- 
pression ? 

Ans. The isothermal. 

564. Is it possible of attainment? 
Ans, Not entirely. 

565. What may be said of the adiabatic method? 
Ans. It is one which should be avoided as much as 

possible. 

566. What are the actual results secured in the best 
compressors ? 



850 Steam Engineering 

Ans. They are intermediate between the two meth- 
ods just mentioned^ but nearer to the second method. 

567. Upon what does the efRciency of an air compres- 
sor depend principally? 

Ans, Upon the effectiveness of the cooling devices. 

568. How many practical methods of removing the 
heat of compression are there? 

Ans, Two — jacket cooling, and intercooling. 

569. Is jacket cooling of the compressor-cylinder ef- 
fective ? 

Ans. Not entirely, except with single-stage compres- 
sion. 

570. What is an intercooler? 

Ans, It is a cooling device interposed between the 
cylinders of a compound or multi-stage machine, through 
which the air passes on its* way from one cylinder to 
the next one. 

571. Describe the process of compression by the multi- 
stage method? 

Ans, A multi-stage compressor has two or more cylin 
ders, the intake or low pressure cylinder being the lar- 
gest in diameter, and in which the air is first compressed 
to a low pressure, and then passed on into the next cylin- 
der which is of smaller diameter, where the air is com- 
pressed to a still higher pressure, and so on in increasing 
ratio. 

572. How should the cylinder ratios be proportioned? 
Ans, So that the M. E. P. and the final temperature 

are equal in all the cylinders. 

573. Describe the construction of an intercooler? 
Ans. It usually consists of a nest of tubes through 

which cold water circulates, and between which the stream 
of air passes. 



-I 



Questions and Answers 851 

574. Which method, single-stage, or multi-stage, ap- 
proaches nearest to the theoretical ideal? 

Ans, The multi-stage, with intercoolers. 

575. Mention another point in favor of" multi-stage 
compression ? 

Ans, It permits a higher piston speed, thus econo- 
mizing in steam. 

576. What is one of the greatest difficulties encoun- 
tered in air power transmission? 

Ans, Freezing of the moisture in the air, either in 
the pipe line, or at the exhaust ports of the air motors. 

577. How may this condition be avoided to a large 
extent ? 

Ans. By the proper cooling of the air during compres- 
sion, which will precipitate the moisture, which may then 
be withdrawn by drain pipes. 

578. What would be the resultant temperature of air 
compressed from atmospheric pressure, and 60° Fahr., to 
a final pressure of 100 lbs., provided there was no cooling 
device ? 

Ans. 484° Fahr. 

579. What effect would this have upon the cylinder 
lubricant ? 

Ans. It would be burned, and be useless. 

580. What would be the temperature of the same 
volume of air if compressed in the first, or intake cylinder 
of a multi-stage machine to a pressure of 25 lbs.? 

Ans. 233° Fahr. 

581. If passed through an intercooler on its way to 
cylinder No. 2, what would its temperature be ? 

■ Ans. It would be brought back to its original tem- 
perature of 60° Fahr. and enter the second cylinder under 
a pressure of 25 lbs. 



852 Steam Engineering 

582. What would the temperature of the same air be 
if compressed in cylinder No. 2 from 25 lbs. to 100 lbs. 
pressure ? 

Ans, It would be but little in excess of that attained 
in the first cylinder, viz., 233° Fahr. 

583. Why would it not attain the temperature stated 
in the answer to question 578, viz., 484° Fahr. ? 

Ans, Because the heat of compression is a function of 
the number of compressions, and practically independent 
of the initial pressure. 

584. Why is air compression at high altitudes more ex- 
pensive than at sea level? 

Ans. Because the capacity of the compressor decreases 
in a greater ratio than does the power necessary to com- 
press. 

585. At an elevation of 10,000 ft. above sea level, 
what is the increase in expense ? 

Ans, Over 20 per cent. 

586. Wliat should be the first care in the installation ' 
of an air compressor? 

Ans. To provide a suitable foundation. 

587. What precautions should be observed in the pip- 
ing? 

Ans. First, there should be as few L's as possible, and 
second, all pipes should be thoroughly cleaned before start- 
ing the compressor; third, allowance should be made for 
expansion. 

588; What is the function of the unloader on the In- 
gersoU-Eand air compressor? 

Ans. To take the load off the air piston when the pres- 
sure reaches the desired point. 

589. What is the function of the regulator? 



Questions and Answers 853 

Ans, To regulate the supply of steam to the steam 
end of the compressor. 

590. What type of air inlet valves is this compressor 
equipped with? 

Ans, Piston inlet valves. 

591. Describe the action of these valves? 

Ans. The air enters and passes through the piston^ thus 
tending to keep it cooled. 

592. What is the function of the Mason pump gov- 
ernor^ with which some air compressors are equipped? 

Ans, To maintain a constant speed regardless of the 
load. 

593. What kind of inlet valves is the Dallett air com- 
pressor fitted with? 

Ans. Either mechanically operated valves^ or auto- 
matic poppet valves^ as desired. 

594. With what type of valves are the AUis-Chalmers 
air compressors usually equipped? 

Ans. Eotary valves for the inlet^ and single-beat poppet 
valves for the discharge. 

595. How are the inlet valves operated? 

Ans, By an eccentric on the main shafts and a wrist 
plate. 

596. What other type of valve-gear are some of these 
compressors equipped with? 

Ans. Both inlet;, and discharge valves are actuated by 
independent eccentrics on the main shaft. 



Refrigeration 



The process of refrigeration consists in the abstraction 
of heat from a substance^ and if air^ water, or ice is at 
hand at a lower temperature than it is desired to attain 
in the body or substance to be cooled, the cooling element 
may be employed to perform the refrigeration directly 
without the aid of a machine. 

If a temperature of 32 degrees and not lower is de- 
sired ice can be used directly, but if it is necessary to 
reach a temperature lower than 32 degrees, a mixture of 
salt and ice or other freezing mixture must be used. 

By mixing one pound of calcium chloride with 0.7 lbs. 
of snow a solution is produced which will give a tempera- 
ture of 67° below zero. But freezing mixtures are too 
expensive to be used for practical purposes, and it there- 
fore becomes necessary to employ machinery. 

The theory and practice of mechanical refrigeration are 
based upon the two first laws of thermo-dynamics, that 
is to say, first: that mechanical energy and heat are 
mutually convertible; and second, that an external agent 
is necessary in order to complete or bring about the trans- 
formation. 

The generally accepted theory concerning the nature of 
heat together with definitions of the terms, specific heat, 
latent heat, the mechanical equivalent of heat, etc., are 
fully discussed in another section of this book and there- 
fore it will not be necessary to enlarge upon these sub- 
jects in this connection except to state that the phrase 
commonly used, "^^heat is generated by compression,^^ is 

855 



856 Steam Engineering 

somewhat misleading^ because the amount of heat in the 
universe is a fixed quantity^ and the intrinsic energy 
possessed by any gas is^ under given conditions a quantity 
that can be actually calculated. Thus if a pound of 
air at a temperature of 70 degrees Fahrenheit, and at 
normal atmospheric pressure be taken as an example, the 
total quantity of energy it possesses is at once known. 
If this air be placed in a compressor, and its volume be 
reduced to say one-half of its original volume, and if 
this be done so rapidly that there is no time for heat to 
escape at the end of the compression, that is to say, adia- 
batically or instantaneous compression without transmis- 
sion of heat, then its energy, will have been increased by 
the amount of work done upon it. Its static pressure 
will be increased, and its temperature will also have risen, 
by reason of its changed state or condition internally. 
Now if the temperature be reduced to its former amount, 
that is to say, to 70 degrees Fahrenheit, its volume will 
contract, so that a small additional quantity of air will 
have to be forced in in order that the pressure may re- 
main unchanged as the temperature is reduced. It will 
be seen that there will be now, consequently upon the 
above, rather more than a pound of air to deal with at 
the higher pressure, and this is what actually occurs in 
practice, but is a point which is easily overlooked. Jfow 
if this air be allowed to expand in a cylinder, it will,| 
give up more of its heat in order to overcome the resist- 
ance, and in this way it will lose or part with more heat. 
The amount of work done is shown by the indicator card, 
and can be estimated. The mechanical work done by the 
air in this expansion is exactly the same as that done 
upon it during its compression, but there is in addition 
the further loss of energy, due to the internal work done 



Refrigeration 857 

in the air during the expansion, so that what has been 
^ done to the air during the entire process has been to 
ji extract some of its original store of heat, thus reducing 
t its temperature ; and the cold air is now ready to restore 
; its deficiency at the expense of the surrounding hotter 
: bodies. 

It should be borne in mind by the student that all 
bodies contain more or less heat and that heat can neither 
be created nor destroyed because it remains a fixed quan- 
tity throughout the universe. 

Therefore the only method by which the temperature 
of a body or substance can be reduced is by the trans- 
ference of more or less of the heat contained in the body 
to some other hoAj or substance. 

The work demanded of a refrigerating machine is to 
extract heat from a body, say from the air in an enclosed 
f; space, such as a refrigerating chamber, and by the ex- 
[ penditure of mechanical energy, to sufficiently raise the 
-temperature of this heat to admit of its being carried 
away by a suitable external agent, the latter being most 
3 usually water, which is not only the cheapest one avail- 
* able, but also has a greater capacity for heat, weight for 
^weight, than any other known substance, and is taken as 
Hhe standard of comparison, its specific heat being taken 
1 as unity. 

1 A refrigerating or ice-making machine may then prop- 
lerly be defined as a heat-pump for the simple reason that 

cits main function is the abstraction of heat from one 

2 body (the body to be cooled), and continuously and auto- 
li matically transferring that heat to the refrigerating or 
6 cooling agent. 



858 Steam Engineering 

REFRIGERATING MACHINES. 

The various inventions for refrigerating and ice-making 
that are now in nse^ can be conveniently classified for the 
present purpose under the following five principal heads, 
viz. : 

First, those wherein the more or less rapid dissolution, 
or liquefaction of a solid is utilized to abstract heat. 
This is, strictly speaking, more a chemical process. 

Second, those wherein the abstraction of heat is effected 
by the evaporation of a portion of the liquid to be cooled, 
the process being assisted by an air-pump. This is known 
as the vacuum system. 

Third, those wherein the abstraction of heat is effected 
by the evaporation of a separate refrigerating agent of 
a more or less volatile nature, which agent is subsequently 
restored to its original physical condition by mechanical 
compression and cooling. This is called' the compression 
system. 

Fourth, those wherein the abstraction of heat is ef- 
fected by the evaporation of a separate refrigerating agent 
of more or less volatile nature under the direct action 
of heat, which agent again enters in solution with a 
liquid. This is termed the absorption system. 

Fifth, those wherein air or other gas is first compressed, 
then cooled, and afterwards permitted to expand whilst 
doing work, or practically by first applying heat, so as 
to ultimately produce cold. These are usually designated 
as cold-air machines. 

Of the various systems of refrigeration using different 
refrigerating mediums, only two. namely, the ammonia 
compression system and the ammonia absorption system 
have come into anything like general use in this country. 



Refrigerating Machines 859 

and these two systems the author proposes to take up and 
discuss in a practical way beginning with the compression 
system. 

A compression plant consists of a high-pressure system 
made up of a condensing coil surrounded by cooling water, 
with pipes connecting it to the compressor and regulating 
valve^ and a low-pressure system consisting of an evapo- 
rating coil surrounded by brine^ or open to the cold cham- 
ber^ with connecting pipes. A small brine pump for circu- 
lating the brine is required. 

In this system the process of refrigeration is divided 
into three distinct stages^ viz., compression, condensation, 
and expansion. 

Anhydrous ammonia is selected as the refrigerating 
medium on account of its low boiling point ( — 28.6° F.), 
its high latent heat of vaporization, its non-corrosive 
effect on iron and steel, and because the pressures under 
which it is used are such as to render it perfectly safe 
to handle with properly constructed apparatus. 

When nitrogen and hydrogen combine to form ammonia, 
one volume of nitrogen unites with three volumes of hy- 
drogen, hence the chemical formula of ammonia is ISTHg. 
As the atomic weight of nitrogen is 14 and of hydro- 
gen 1, the formula also indicates that 14 parts, by weight, 
of nitrogen, combine with 3 parts of hydrogen, to create 
17 parts of ammonia. 

Gaseous ammonia can be liquefied at a pressure of 128 
lbs. to the square inch, at a temperature of 70° Pahr., and 
at a pressure of 150 lbs. at a temperature of 77° Fahr., 
the pressure required to produce liquefaction rising very 
rapidly with the temperature. To liquefy by cold it re- 
quires to be reduced to a very low temperature, viz., — 85. S"" 
Pahr. 



860 Steam Engineering 

Thd gaseous iammonia is drawn into the ammonia com* 
pressor^ or pnmp^ and is there compressed to a pressure 
varying from 125 to. 175 pounds per square inch. 

During this compression^ the latent heat of the vapor 
(that is^ that quantity of heat which was imparted to it 
to effect its expansion from a liquid to a vapor) is con- 
verted into active or sensible heat. 

The vapor^ under this high pressure, is forced into the 
condenser, consisting of a series of pipes over which cold 
water is allowed to flow (atmospheric condenser), or 
through pipe coils submerged in a body of cold water 
(submerged condenser), where the now active and sen- 
sible heat developed during compression is transferred 
to the cooling water, thus withdrawing from the vapor 
that heat which was necessary to keep it in a gaseous 
condition, and re-converting it into a liquid at the tern- i 
perature and pressure existing in the condenser. ^ n 

The ammonia, so liquefied in the condenser, is then 
allowed to pass in small quantities through a regulating 
or expansion valve into pipe coils placed in the rooms 
to be cooled, or in a bath of brine, when it again expands 
into a vapor, owing to the lower pressure maintained in 
such pipes, taking up from whatever substance surrounds 
it, an amount of heat exactly equivalent to that which was 
given up during condensation. 

The expanded vapor is then drawn back into the com- 
pressor, again compressed, condensed, and expanded, the 
cycle of operation being repeated indefinitely with the 
same ammonia, which is used continuously and which 
never comes in contact with the substance to be refrig^ 
erated. 

There are two systems of refrigeration by compression 
viz., the "wef ^ system and the ^^dry^^ system. 



va] 






tort 



Refrigerating Machines 861 

A dry compression plant with an expansion evaporating 
system requires: 

One. A medium size compressor. 

Two. A large size evaporating system. 

Three. A large amount of ammonia. 

On the other hand, a wet compression plant having a 
wet compression evaporating sytem requires: 

One. A large size compressor. 

Two. A medium size evaporating system. 

Three. A medium quantity of ammonia. 

According to A^ollman the ^Vet'^ system has the fol- 
lowing advantages over the ^'^dry^^ compression system: 

One. '^By allowing the ammonia vapors to return to 
the compressor in a partially wet state^, we are enabled to 
work with a higher back pressure, thereby having the am- 
monia gas in the refrigerator pipes of a higher density 
than if the vapors were perfectly dry. Furthermore, we 
are. enabled to keep the refrigerator pipes partially filled 
with liquid ammonia, in consequence of which the surface 
of the refrigerator can be materially reduced.^^ 
! Two. ^^By keeping the compressor parts at a cool tem- 
tperature, the compressor draws in a greater amount of 
<vapors than where the parts are highly overheated. With 
ta dry compressor, although the cylinder is water- jacketed, 
■the internal parts are kept at a very high temperature, 
-and when the dry ammonia vapors are drawn into the 
ifeompressor, they immediately get heated up, and by ex- 
iPpanding prevent the compressor from drawing in its full 
amount of vapors.^^ 

Three. ^^By keeping the compressor at a cool tempera- 
■'ture, the compressor oil which is taken into the compres- 
sor through the stuffing box cannot evaporate, but is kept 

1. 



862 Steam Engineering 

in its liquid state^ and as such deposited in the oil col- 
lector/' 

Four. ^^With the wet compressor system, the engineer 
in charge knows if sufficient ammonia is circulated through 
the system or not, by placing his hand on the delivery pipe. 
If this is fairly warm, a sufficient amount of ammonia is 
passed through the system.^' 

Eegarding Vollman's theory (2), that a larger vol- 
ume of vapor could be handled by the wet compressor at 
each stroke, the fact must not be overlooked that the in- 
terchange of heat between the ammonia and the walls 
of the compressor cylinder is much greater than is gen- 
erally anticipated. With the vapor wet after compression, 
the capacity of the plant is reduced, and also the coefficient 
of performance, so that this condition should be avoided. 
When superheating is allowed, the capacity is increased, 
but again the ideal coefficient of performance is reduced 
slightly. Experiments seem to indicate, however, that a jj] 
moderate amount of superheat, say 10° to 20°, results in ^^ 
a decided improvement in efficiency. This may be due 
to the reduction thereby caused in the mechanical losses 
inside the cylinder, and also in the heat leakage into the 
ammonia vapor from the cylinder walls during compres- 
sion. But this is more or less counterbalanced by the 
widening of the temperature range, so that the coefficient | 
of performance may be reduced, may remain steady, or 
may be increased according to the charge of ammonia 
present. 

On the whole there does not seem to be much to choose 
between "wet^^ and "dry'' compression. The former gives i 
a slightly higher coefficient of performance, the latter a j 
slightly greater amount of refrigeration. 



Linde Ice Machine 863 

.THE LINDE ICE MACHINE. 

As the Linde ice machine^ Fig. 357, is a good example 
of the workings of the "wet^^ or humid system, a short de- 
scription of the construction and operation of the machine 
will be given. 

The theory of the action of the Linde machine is as 
follows : 

^^So long as ammonia vapor is in a humid or saturated 
condition (that is, while still in contact with any of its 
originating liquid), temperature and pressure are func- 
tions of one another, and to a given temperature belongs 
a certain pressure. 

^^On the contrary, when ammonia (now properly called 
a gas) is not in contact with any of its mother liquid, its 
temperature may be very much higher than that corre- 
sponding to its pressure. 

"For example, the pressure of the steam in a boiler de- 
pends entirely upon its temperature, which is always equal 
to that of the remaining water. It is therefore evident 
that in the case of steam, while in contact with the origi- 
nating water, temperature and pressure are interdepen- 
dent. 

"Separate the steam from the water, and apply heat (su- 
perheat it), and it may have the same pressure at widely 
; different temperatures.^^ 

When a gas or vapor is compressed, the heat equiva- 
lent of the mechanical work of compression tends to raise 
its temperature, and consequently its pressure, more rap- 
. idly than would be the case if it would be maintained at 
^1 constant temperature. 

In the compression of a dry gas, unless heat is with- 
drawn by means of a water-jacket, or other cooling device, 



864 



Steam Engineering 




s 



oo ■ 
o 



Linde Ice Machine 



865 



the adiabatic curve will be traced on the indicator dia- 
gram. This is the curve which represents the compression 
or expansion of a gas without loss or gain of heat. 

In the Linde machine the cooling of the vapor in the 
compression cylinder is effected by the introduction into 
the latter of a small quantity of liquid ammonia with 
the gas or vapor at the commencement of each stroke. 



\so^He.?*.M>fcs\- . 



yCvO l.^ a y©s.T \C. 



CO 

J 

o 
in 



Spring 60 

M. E. P. 59 Lbs. 
..- Area 0.05°' 
.«- Area 0.69°' 




•5 



Dry Gas. 
Fig. 358 

whereby it is cooled down to a refrigerating temperature. 
The ammonia is carried back to the compressor in a sat- 
urated condition, and the heat of compression is taken 
care of in the unexpanded ammonia which in the form of 
I fog or vapor, entered the compressor on the suction stroke. 
The diagrams Figs. 358 and 359 illustrate the compara- 
tive efficiency of this method of cooling the compression 



866 



Steam Engineering 



cylinder^ termed the *^Vet^^ system^ and the other method 
wherein a water-jacket system is employed termed the 
^^dry^^ gas system. 

The initial volume and pressure^ and the terminal pres- 
sure are the same in each case. In the compression of 
the dry gas^ the compression curve necessarily follows for 
a considerable distance the adiabatic line. 



ISO'THe.R.M^ftwU \ \ /5*»C»\A»*^^^T\C. 



Spring 60 
M. E. P. 53 Lbs. 
Area 0.4°' 
. Area 0.34° 




Saturated Vapor. 
Fig. 359 



This for the reason that the gas coming mtc the cylin- 
der from the expansion coils is at a temperature of — 5° 
F. and no heat can be transmitted from it to the cooling 
water in the water-jacket until the temperature of the 
gas has been raised above that of the water, which is prob- 
ably 60^ to 70° F. 



Linde Ice Machine 



867 



The compression curve then leaves the adiabatic and 
during the last part of the stroke^ before the discharge 
valve opens^ approaches the isothermal line. 

In the compression of saturated vapor^ the unexpanded 
ammonia begins immediately to absorb the heat of com- 
pression, and the compression curve at once leaves the 
adiabatic and approaches the isothermal linC;, making a 




Fig. 360 
sectional view of the linde compressor cylinder and valves 

diagram that is much smaller in area and which therefore 
represents work requiring less power. 

The efficiency ratio of any cylinder cooling device is 
found by dividing the area between the acttial compression 
curve and the adiabatic curve, by the total area between 
the adiabatic and isothermal curves. 

'^Assuming that the diagrams shown are from eighteen 
by thirty inch double-acting compressors, running at fifty 



868 Steam Engineering 

revolutions per minute, the effective horse-power required 
for the compression of the saturated vapor would be 
102.1 horse-power^ as against 113.7 horse-power for the 
dry-gas machine, a gain of 10.2% m favor of the humid 
system of operation/' 

Fig. 360 shows a sectional view of the Linde compres- 
sor cylinder, piston and valves. 

It will be observed that the piston and heads are 
spherical and of the same radius. The valve discs con- 
form absolutely to this radius, and when the valves are 
seated these discs are exactly flush with the heads. 

The clearance between the piston and the cylinder head 
is very small, being only 3^2 in., therefore the clearance 
losses are very small, being less than two per cent, of the 
total cjdinder volume. The cylinders are made of clear, 
hard iron, tested to 1,000 lbs. hydrostatic pressure. The 
finishing cut through the cylinder is made after it is 
placed in the frame, the final cut on crosshead guides 
being taken at the same time, and on the same boring 
bar, thus insuring their correct alignment. Proper open- 
ings are provided for the application of the indicator. 

The lubrication of the piston is accomplished in large 
measure by the moisture in the ammonia itself. Oil is 
used to seal the stuffing box against the leakage of am- 
monia. Very little of this oil is carried into the cylinder 
on the piston rod. 

The piston is ground on the tapered shoulder of the 
piston rod, and is secured by lock nuts, as shown in Fig. 
360. The follower head is then screwed on and held 
firmly in place by the flush nut, which in turn is pre- 
vented from backing off by a screw set into the face of 
the follower and riveted over. Those who have expe- 
rienced the annoying effect of pistons working loose on 



Linde Ice Machine 869 

the rod will appreciate the advantages of this method^ per- 
mitting^ as it does^ the ready removal of the piston when 
necessary^ while at the same time absolutely precluding 
the possibility of its accidentally becoming loose. Many 
serious accidents have resulted from inattention to this 
detail. The piston is packed with removable bull rings 
and cast-iron packing rings. 

The valves are of large area^, the discharge valve being 
placed at the lowest point of the cylinder^ insuring the 
perfect draining of any liquid present at the end of the 
compression period. The importance of this feature- can- 
not be overestimated; the many records of compressors 
wrecked by the piston coming in contact with incompres- 
sible liquid being familiar to all users of this class' of 
machinery. The stems and discs are of the finest forged 
steely set in cast-steel housings. The valve lift is gov- 
erned by positive stops and controlled by springs. The 
suction valve is provided with a safety stop to prevent 
, its falling into the cylinder. 

The Linde stuffing-box is shown in section, in Fig. 361 
— to which reference is now made. The numbers 2, 4, 
5, 9, 10, 12 and 14 indicate composition packing rings. 
These should never be used solid but should be cut as 
shown in sketch ^'^A.^^ Numbers 3, 6, 8 and 11 repre- 
sent metal rings, made from pure tin. They are intended 
to keep the rubber rings in proper condition. These rings 
should always be one-sixteenth of an inch larger than the 
rod, and should never be cut in two, as otherwise they 
, are apt to score the rod. If necessary to put in new metal 
i rings, disconnect the piston rod from the crosshead and 
! slip the rings over the end of the rod. Under no circum- 
stances pack the compressor ivithout the metal rings. 



_ 




Fig. 861 
sectional view of linde stuffing box 



f 



Linde Ice Machine 



871 



N'umber 7 designates the lantern which forms an oil 
storage in the middle of the stuffing box. The oil supply 
is taken in at the point marked "^^a'' through a pipe con- 
nection from the oil trap. This passage being always 
open^, the oil is forced into the stuffing-box by the high 
pressure gas in the oil trap^ keeping this stuffing-box 
and lantern always full^ and instantly replacing what little 
oil is carried into the cylinder on the rod. ISTumber 13 
is the stuffing-box gland which is supplied with oil through 




Fig. 362 
12-ton linde ice machine — motor operated 



the inlet "b^^ from a small oil pump operated from the 
main shaft. This oil overflows at "c'^ and is led back 
to the oil pan to be recirculated. 

ISTumber 15 is the oil gland which should be kept just 
tight enough to keep the oil in the stuffing-box gland. 
The points of contact with the rod are numbers 1, 13, 
and 15, and they must fit the rod properly. If it becomes 
scored and is turned down, these parts must be rebab- 
I bitted. 



872 Steam Engineering 

When repacking be sure to place the different parts of 
the packing in strict accordance with the above instruc- 
tions and with the cut shown^ insuring the best results. 
Great care should be used not to tighten the stuffing 
gland 13 more than is necessary to prevent the ammonia 
from leaking. 

The Linde compressor is of the horizontal double-acting 
type^ and consequently the lines of strain are brought c 
close to^ and parallel with the foundations. The machine 
is so constructed^ as to be easily attached to any steam \ 
engine, either by being direct connected, or by belting 
from a counter shaft. In small plants, electric motors 
are often used for operating these machines. Pig. 362 
shows an installation of this kind. 



DE LA VERGXE REFRIGERATI^^G MACHINE. 

In the De La Vergne refrigerating machine the cooling 
of the heated gas is effected by passing it through pipes 
surrounded by running water. The characteristic feature 
of this machine consists in the patented system for pre- 
venting the occurrence of any leakage of gas taking place 
past the stuffing-box, piston, and valves, and of extract- 
ing the heat from the gas during compression, by the 
simple device of injecting into the compressor, at each 
stroke, a certain quantit}^ of oil or other suitable lubricat- 
ing fluid. By means of this sealing, lubricating, and cool- 
ing oil, not only are the stuffing-box, piston, and valves 
effectually sealed, and the heat developed during compres- 
sion taken up, but all clearances are entirely filled up. j 
This latter is a matter of great importance, as it ensures ' 
a complete discharge of the gas from the pump cylinder, 
and obviates the above-mentioned loss of power and effi- 
ciency. 



De La Vergne Refrigerator 



873 



This metliod of sealing the stuffing-box and piston pre- 
vents leakage and consequent introduction of air into 
the pump^ or wasting of the refrigerating gas at each 
alternate stroke of the piston without necessitating the 
packing of piston so tightly as to cause excessive friction. 
Fig. 363 shows a sectional view of a double-acting De La 
Vergne compressor fitted with Louis Block^s arrangement 
of valves^ the main object of which is to secure the dis- 
charge of the oil at the lower end of the cylinder taking 
place immediately after all the gas is gone and not be- 




FiG. 363 

DOUBLE-ACTING TYPE OF DE LA VERGNE AMMONIA COMPRESSOR 

.^fore^ as in the latter case re-expansion will take place, 
iresulting in loss of efficiency of the pump. To effect this, 
-two valves are provided in the lower end of the compressor 
■cylinder, one above the other. 

; Either, or both of these valves may open on the down 
-stroke of the piston, until the latter covers the upper 
.one, when only the lower one is left open to the condenser. 
fDuring the remainder of the stroke of the piston, after 

the lower valve is also closed, the other or upper one 
-opens communication with an annular chamber formed 

in the said piston. In the bottom of this annular cham- 



874 Steam Engineering 

ber are provided^ moreover^ valves which open as soon 
as all the other outlets from the underside of the piston 
are closed^ to ensure which they are loaded with springs, 
so arranged as to require somewhat more pressure to 
open them than the discharge valves on the side of the 
cylinder. The gas, and afterwards the oil, then all pass 
out through the piston, no trace of the former being 
present at the completion of the down stroke. In this 
manner the oil system of sealing can be advantageously 
retained, and the pump will work as well at the lower 
side as the upper. 

Fig. 364 shows a complete installation of a refrigera- 
ting plant on the De La A^ergne system, the vertical com- 
pressor being driven by a horizontal engine. The cir- 
culation of the ammonia, and the sealing oil is as fol- 
lows: A is the compressor cylinder, double-acting, and 
similar in construction to that shown in section in Pig. 
363. E is the steam engine cylinder. B is the pipe 
through which the gas is drawn from the evaporating 
coils into the compressor A. The gas is then discharged 
by the action of the compressor through the pipe C, into 
the pressure tank D, where the sealing oil or liquid falls 
to the bottom. Suitable cast-iron baffle plates are fitted 
in the upper portion of the pressure tank, which serve 
to retain the oil, and insure its deposition. From the 
pressure tank D the gas which still retains the heat due 
to compression, passes through pipe e into the bottom 
or lower pipe of the condenser r, wherein, by the cooling 
action of cold water running over the pipes, the heated 
gas is first cooled and then liquefied. The ammonia, in 
this liquid condition, is then led by the small liquid pipes 
G^ through the liquid header h^ into the storage tank i, 
from whence it flows through the pipe J into the lower 



De La Vergne Refrigerator 



875 




Fig. 364 
complete installation of a de la vergne refrigerating plant 



876 - Steam Engineering 

part of the separating tank k^ which latter must be con- 
stantly maintained at the very least three-qnarters full. 
L is a pipe of small bore, through which the liquid am- 
monia is forced, by reason of the pressure to which it 
is now subjected, to the expansion cock or valve, through 
which it is injected into the evaporating or expansion 
coil N which is situated in the room or chamber to be 
refrigerated or cooled. 

The ammonia gas resulting from the expansion and 
evaporation of the liquid ammonia in the evaporating or 
expansion coil n^ having absorbed or taken up the heat 
from the surrounding atmosphere, passes away through 
the pipes o and b^ back again into the compressor cylin- 
der, and the cycle of operations of compressing, etc., are 
again performed as above. 

Secondly. Following the course of the oil employed 
for sealing, lubricating, and cooling purposes, which, as 
previously mentioned, is heated with the gas during com- 
pression, and is passed into the tank D^ to the bottom of 
which it falls. Prom the bottom of the tank D, the heated 
oil is conducted through a pipe a to the lowermost pipe 
of the oil-cooler b, which is practically similar in con- 
struction, but on a smaller scale, to the ammonia con- 
denser, and is likewise cooled by sprayed or atomized 
cold water. After being sufficiently reduced in tempera- 
ture in the oil-cooler b, the oil flows through the pipe c, 
strainer d, and pipe e, into the oil pump f, which latter 
is so constructed that it delivers the cooled oil into the 
compressor, distributing it to either side of the piston or 
plunger during its compression stroke, that is to say, in 
such a manner that no oil is furnished during the suction 
stroke of the piston, but only during the time of com- 
pressing, thereby cooling the gas during its period ofB 



De La Vergne Refrigerator 



877 



heating. The heated oil, after leaving the compressor, 
then again returns, together with the hot compressed gas, 
to the pressure tank D^ and follows the same round through 
the oil-cooler b, strainer d, and oil pump f, back to the 
compression cylinder. It will be obvious that the oil, as 
well as the ammonia, is used over and over again, no loss 
or waste of either taking place except that which may 
occur through leakage. 




Fig. 365 
diagram from de la vergne compressor 

J Any small quantities of oil, however, that may be car- 

-ried over with the current of the gas from the pressure 

tank D into the condenser f, pass along with the liquid 

ammonia into the separating tank k^ where, by reason 

^of its greater weight, this oil falls to, and collects at the 

"bottom of the tank. As soon as a sufficient quantity of 

ioil has become thus deposited, it is drawn off, and passed 

through the oil cooler back to the oil pump. The oil 

-reservoir or tank is also connected to the oil pump f. 

IiWhen the apparatus is employed for the manufacture of 



878 Steam Engineering 

ice^ the evaporating coils N are placed in a tank contain- 
ing brine^ sufficient space being left between them to 
allow of the insertion of cans or moulds containing the 
water to be frozen. As before stated^ the exhaust steam 
of the engine driving the compressor is condensed and 
purified^ and supplies the water to be made into ice. 

The various parts are clearly indicated in Fig. 364 — 
and the routes taken by the ammonia, the sealing oil, the 
lubricating and cooling oil, and the steam are shown by 
the arrows. 

THE TRIUMPH ICE MACHINE. 

Fig. 366 shows a sectional view of the compressor cylin- 
der and valves of the Triumph double-acting ammonia 
compressor. 

It will be seen from the illustration that the compres- 
sor is provided with five valves, viz., three suction valves 
and two discharge valves, the third, or auxiliary suction 
valve, being much lighter than the main valves, and per- 
fectly balanced, and it being claimed by the makers tending ' 
greatly to increase the economy of the machine. 

Obviously the main suction valves must necessarily be 
of sufficient dimensions to admit the charge quickly at 
the commencement of each stroke, and the springs con- 
trolling them must consequently have an appreciable ten- 
sion. It will be readily seen that owing to this fact the 
pressure of the gas in the cylinder, during admission, 
must be less than it is in the suction pipe by an amount 
equal to the tension of these springs. By the use of the 
above mentioned third, or auxiliary suction valve, which 
is comparatively light, and is consequently operated with 
a very light spring, the pressures in the compressor pump 



I 



Triumph Ice Machine 



879 



are equalized, and a fuller charge is obtained at each 
stroke, thereby increasing the efficiency of the machine. 

The valves comprise each a guard screwed on to the 
stem, fitted inside a cage, and so ribbed as to reduce the 
port area, the bottom of the stem being enlarged for that 
reason. 'Stems extending from both the suction and dis- 
charge valves to the exterior, and passing through stuffing- 
boxes, admit of their being adjusted from the outside. 




Fig. 366 

double- action horizontal type of triumph ammonia 

compressor 

and any desired degree of tension being put upon the 
springs. The object of this arrangement is to adjust the 
machine for working at different pressures, and the rela- 
! tive temperatures thereof. 

' There are three packing compartments in the piston- 
• rod stuffing-box, and it is fitted with a suitable relief valve 
(Communicating with the suction. The heads are formed 
1 concave, and of a radius which enables a larger valve 
'area to be secured. The principal shut-off valves are of 



tiSO steam Engineering 

such a form of construction as to admit of their being 
packed while the machine is workings and a feature in 
the design of this machine which is of by no means in- 
considerable advantage^ is that every portion of the com- 
pressor is easily accessible. 

CONSOLIDATED REFRIGERATING MACHINE. 

Fig. 367 shows the general form of the Consolidated 
ice-making and refrigerating machine. It is a compres- 
sion type of machine^ having two single-actings vertical 
compressors^ and either a horizontal or a vertical engine^ 
which is connected to a center cranky on either side of 
which are large journal bearings. Power thus transmitted 
to the shaft is regulated by two flywheels which are of 
sufficient weight to carry the engine smoothly over the 
point of maximum compression^ and to deliver the power 
to the compressor. 

It is an advantage to have the crank in the center of 
the shafts, and to place a flywheel between the engine crank 
and each pump cranky because this construction gives 
uniformity and steadiness of motion and diminishes tor- 
sional strain, vibration and friction of the crank shaft. 
It also permits the use of a long-stroke Corliss engine, since 
the stroke of the engine is not limited to the stroke of the 
ammonia pump, as is the case where the compressor and 
engine are connected to the same crank pin. In this way, 
the builders claim to effect a saving of from 10 to 15 
per cent in the steam consumption. 

Heavy pump columns terminate at the bottom in broad 
flanges bolted to a substantial foundation plate, cast in 
one piece and provided with four journal bearings for 
the crank shaft. Convenient stairways and galleries are 



J 



Consolidated Ice Machine 8. 1 

proyided to furnish access to the upper part of the ma- 
chine. As seen in Fig. 368 the compressor or ammonia 
pump is single-actings compressing only on the up-stroke, 
and the gas has free entrance to, and exit from the cylin- 




FiG. 3G7 . 

VERTICAL CONSOLIDATED REFRIGERATING MACHINE 



der below the piston, thus keeping the pump cylinder and 
piston cool. 

An oil chamber, which effectually seals the stuffing-box 
around the pump piston rod, is formed in the lower part 
of the pump. As the pressure on the stuffing-box end of 



882 



Steam Engineering 




Fig. 368 
cross-section of the simple-acting ammonia compressor 

the pump is only the direct evaporator pressure^, there is 
no chance for the escape of ammonia. Equalization of 



Consolidated Ice Machine 



883 



the temperature and cooling of the compressor is effected 
by encasing it in a copper water jacket. 

In the construction of the piston, no bolts or nuts are 
used, and there are, therefore, no cavities or chambers 
into which the gas can be compressed. Since the piston 
travels flush with the pump head, all of the gas is ex- 




-.oi 



Fig. 369 
suction valve showing safety device 

pelled at each stroke. The pistons are fitted with spring 
rings that are first turned elliptical, and afterward re- 
turned on a mandrel until they fit the cylinder exactly. 

As shown in Fig. 368 the stuffing-boxes are operated 
by a worm-gear device so that, while the machine is run- 
«ning, a turn of the hand-wheel accurately adjusts the 



884 Steam Engineering 

stufBng-box gland and tluis makes unnecessary the dif- 
ferent and frequently dangerous use of a wrench or span- 
ner and also avoids the possibility of cutting the piston 
rod by uneven adjustment of the gland. 

Connections for the suction and discharge pipes are 
made outside of the pump head so that, when it is de- 
sired to remove the head^ neither of these connections need 
be disturbed. Discharge and suction valves^ compressor 
heads^ piston and piston rods^ all are easily removed with- 
out breaking any ammonia connections. 

Fig. 368 shows the suction and discharge valves which 
are located in the pump head. The suction valve^ Fig. 369^ 
is balanced^ thus allowing the pump to fill with expanded 
gas from the evaporator with no loss of pressure. As 
shown in Fig. 369, the valves are provided with a safety 
device which renders it impossible for them to get into 
the cylinder. Cushioning of the discharge valves ensures 
noiseless action and, since both suction and discharge 
valves are set in steel cages, and held in position in the 
pump head by means of yokes and set screws, it is but 
a moment's work to remove a valve and put a duplicate 
in place. 

As seen in Fig. 367 the machine is driven by a Feath- 
erstone Corliss engine resting on substantial base plates 
which are extended on one side for the dashpots. The 
valve motion is of the improved Corliss type, having the 
liberating catches made of hardened steel of such form 
that eight wearing surfaces are available, by change of 
position, each new position restoring the valve motion to 
its original setting. 

Horizontal Type, In this form, the Featherstone ma- ] 
chine is built with a horizontal engine and a horizontal, 
double-acting compressor, and has a straight crank shaft 




Fig. 370 
horizontal double-acting machine 



886 Steam Engineering 



I 



with the flywheel placed in the middle between the two 
main bearings as shown in Fig. 370. These machines are 
mounted on the heavy duty Tangye frame which is almost 
universally used by builders of double-acting compressors. 
Provision is made for cooling the compressor cylinder by 
means of a water jacket so that it may be operated as a 
dry^ or humid gas machine. As shown in Fig. 370^, the 
machine is driven by a Featherstone- Corliss engine^ hav- 
ing a heavy frame similar to that of the compressor^ but 
any type of engine may be used and^ if necessary^ the 
compressor can be driven by belt. 

Figure 371 shows the manner in which the compressor 
cylinders are pressed into the frame so as to form a water 
jacket. The valves are placed in the compressor head in 
a way that will permit of their easy removal and^ since 
the discharge valves are located at the lowest part of 
the cylinder^ perfect draining at the end of the compres- 
sion period is assured. This makes it impossible for the 
machine to be wrecked by the piston coming in contact 
with an incompressible liquid at the end of the stroke. 
The clearance is less than 3V inch^ thus giving good 
efficiency by permitting the piston to discharge all of 
the gas at each stroke^ so that on commencing a new 
stroke^ gas is immediately drawn into the cylinder. 

In the horizontal machine^ the valves are like those 
used in the consolidated compressors^ the stems and discs 
being of forged steel set in cast-steel housings. Lift 
of the valves is given by cushion springs and controlled 
by compression springs and the suction valves are of the 
Featherstone safety type^ so that it is impossible for them 
to fall into the cylinder. The piston is screwed to the 
piston rod by a jam nut, and the connecting rod is pro- 




Fig. 871 
section of compressor showing water jacket 



888 Steam Engineering 

vided with adjustable wedges for taking up the wear of 
the boxes. 

In a double-actings ammonia compressor, the stuffing- 
box is one of the most vital parts. Eef erring to Fig. 372, 
letters A, B, C, D, E and F indicate composition split 
packing rings and letters Q, E, S, U, Y and W denote 
pure tin rings of an inside diameter iV inch larger than 
that of the piston rod. These rings should never be split. 

J is a lantern which forms an oil storage reservoir in 
the stuffing-box, the oil being taken in at the point marked 
K from a pipe connected to the oil trap. This passage 
being always open, the oil is forced into the stuffing-box 
by the high pressure of the gas in the oil trap, thus keep- 
ing the lantern full and instantly replacing what little 
oil is carried into the cylinder by the rod. L is a lantern 
which at the point marked M has a pipe connection to 
the suction line so that any ammonia gas which may have 
escaped the packing rings C, D, E and F is drawn back. 
By this device, packing rings A and B have to withstand 
only the suction pressure. IST is the stuffing-box gland 
which has a chamber supplied with oil through from 
a small rotary oil pump operated from the main shaft. 
P is the oil gland which should be kept just tiglit enough 
to keep the oil in the stuffing-box gland. 

Points of contact with the rod are G, H and I and 
they are made an exact fit. If the rod becomes scored 
and is turned down, these parts must be rebabbitted. To 
tighten the stuffing-box gland it is only necessary to ad- 
just the nut T, which is a pinion nut and is in mesh 
with the inside gear and the other two pinion nuts. 

As shown in Fig. 373, the dashpot is of a special de- 
sign, and allows for the adjustment of both vacuum and 
cushion. It is placed on an extension of the cylinder fool 



Consolidated Ice Machine 



889 




Fig. 372 
stuffing-box of the double-acting compressor 

md connected by the usual vertical link rod to the crank 
)n the valve stem. The central cylinder A acts as a 



890 



Steam Engineering 



guide and piston^ while the pot B rises and falls^ and 
by so doing draws air into the chamber C through the 
passage T>, the vacuum C being regulated by the position 
of the needle valve E. As the pot falls^ air escapes from 
C through valve H^ and the fall is free until the lower 
end of the pot cushions into a chamber K formed by 
drawing up the ring P by means of the screw G. The 
position of P determines the amount of the cushioning 
and the leather Avasher E prevents hammering at the end 
of the fall. 




Tig. 373 
section of the dashpot 

Double-pipe Ammonia Condenser. This type of con- 
denser consists of two series of coils^ one within the other, 
and is usually built in four different forms having 2-inch 
and 1.25-inch^ 2.5-inch, 3-inch and 2-inch pipes or, 
having the upper outside pipes 2.5 inches and the lower 
pipes with all of the inner pipes 1.25 inch. Of these forms, 
the first is used most extensively, but the second is used 
whenever extra strong pipe is required, and the third when \i[ 



Double Pipe Ammonia Condenser 



891 



extremely dirty water is to be handled. The ammonia cir- 
culates downwards through the annular space between the 
two sets of pipe coils. By this arrangement a compara- 
tively small charge of ammonia is required^ owing to the 
narrowness of the space between the pipes. 

Occupying small space^ the condenser can be placed in 
a basement or other convenient place. Since the flow of 













- ™^^^ 


^^^^^ 














,Jj^ 


p 


^ 


^^^^g 


■Hh 


Hi 












1^ 






HlHJI 


^^H 


1 










/'■^ 








^HH 


I^H 


1 








■■'-'■•■■■■ Mf 


i^Mfl 








H^^l 


H|^H 


■ 






^'*"" 


1 


^m 








^H 


^B/4§^^ 


i 




"^^^^^H 


■ 




'^^H 








^^^l^^^l 


[^K^^^^ 


:-!g^.::-:.. 






^^^S ' 




^: -^^^B 








^^HH 


^aH 


■ 






p 




^ ~^H 








^^» 


^H 


■ 






B 




''^^^B 








^^H 


^H 


■ 






is 


1 


J 








^^- 


i 


1 
1 




^^^^1^ 


1 




ij 








^s 




1 


I^E°' ; 




main 


te:&: 


:;;l 








1 


1 


P 






^H 



Fig. 374 
return bend for the atmospheric condenser 






fjiammonia gas and the cooling water are in opposite di- 
rectionS;, the hottest gas comes in contact with the hottest 
water and thus fully utilizes the cooling effect of the water. 
Fig. 374 shows a sectional view of tfie atmospheric 
condenser return bend, and Fig. 375 a view of the return 
/bend which is used for the double-pipe ammonia con- 
ildenser and also for the brine cooler. Fig. 376 shows 



892 



Steam Engineering 



the double-pipe condenser in which^ owing to the con- 
struction of the return bend^ it is possible to remove and 
replace any length of pipe without tearing down the 
whole coil as is necessary where double-pipe connections 
are made with screwed bends. 

Condensers are furnished complete with gas, liquid, 
pump-out^ and water headers and one of the special fea- 
tures is the construction of the liquid and purge head- 
ers which are made with special tee valves. Owing to 
the design, additional sections can be added at any time 
as enlargement of the plant may require. 




Fig. 375 
double-pipe return bend 

Pig. 377 shows a double-pipe brine cooler, which is 
built on the same general plan as the ammonia con- 
denser, but is made of 2 and 3-inch pipes. Liquid am- 
monia enters and is expanded in the bottom pipe and the 
gas is drawn off at the top, while the brine is pumped 
into the top and circulates downward, through the an- 
nular space between the two pipes. 

There are two distinct methods of utilizing refriger- 
ation, viz., the Brine System and the Direct Expansion 
System. In the former the coils of pipe in which the 
ammonia is expanded are placed in a tank containing a 



*«^" 1 ■ 


aa 

. ; 1 


.pi ' ■ M 


Wfi 



Fig. 376 
double-pipe ammonia condenser 




Fig. 377 
double-pipe brine cooler 



Brine, and Direct Expansion Systems 895 

solution of salt;, or calcium chloride of such density as 
to insure a low freezing point. This body of brine^ after 
being reduced to a low temperature by the transfer of 
its heat to the expanding ammonia^ is pumped through 
coils of pipe in the rooms to be cooled^ taking up from 
the atmosphere of such rooms a part of its heat. It is 
then returned to the brine tank^ recooled and again cir- 
culated through the rooms. 

In the direct expansion system^ the expansion pipes 
are placed in the rooms to be cooled^ the heat necessary 
for the expansion of the ammonia being drawn directly 
from the atmosphere surrounding the pipes. 

Of the two systems^ the direct expansion system is 
probably the most efficient as may be seen by the follow- 
ing summary of its advantages over the brine system: 

1st. All intermediate agencies are dispensed with^ the 
refrigeration being produced at the place where it is uti- 
lized. Every transfer of energy means loss. The brine 
^tank^ even if insulated^ furnishes immense surface for 
loss by radiation. 

2d. The Avhole plant is much simpler^ considerable aux- 
iliary apparatus^ such as pumps^ etc.^ is unnecessary^. the 
requirement of power is therefore reduced^ and repairs are 
correspondingly lessened. 

3d. The expansion surface is enlarged and better dis- 
tributed^ making possible the using of the entire capacity 
of the compressor to the best advantage. 

4th. The ammonia is expanded at a much higher tem- 
perature and pressure^ and is therefore drawn back to the 
compressor at higher density^ resulting in the machine cir- 
culating a much greater weight of ammonia per minute. 
Each pound of ammonia has just so much potential re- 
frigerating energy^ and the capacity of a compressor is 



896 Steam Engineering 

therefore dependent solely upon the weight of ammonia 
pumped in a given time. For example^ if it is desired 
to maintain a temperature of 32° F. in a certain room, 
it will require a compressor displacement of 22 per cent 
more with the brine system than with direct expansion, 

5th. The brine system is much more expensive to in- 
stall^ owing to the far greater quantity of pipe required, 
the additional pumps, tanks, etc. 

One of the advantages claimed for the brine system is 
the ability to store refrigerating energy in the brine tank, 
which may be drawn upon during the night, thus ren- 
dering the continued operation of the compressor unnec- 
essary. It has been claimed that by doing this the fuel 
consumption is reduced; but this is not good logic, since 
just so much work must be done to produce a given quan- 
tity of refrigeration, and it makes no difference whether 
this work is distributed throughout the twenty- four hours, 
or is crowded into a shorter period. If the work is to 
be done in a short time the compressor must be corre- 
spondingly larger. 

The development of the ice-making industry during 
the* past ten years has been astonishingly rapid. This 
may be attributed to the fact that the ice-using public 
has come to a realization of the vast superiority, from 
a hygienic standpoint, of manufactured, over natural ice, 
and to the further fact that owners of electric light plants, 
mills, water-works and other power plants have found 
that the ice-making business is one that is peculiarly 
adapted to being operated in combination with other in- 
dustries requiring the use of power. 

Ice Making, Ice is made artificially by either the can 
system or plate system. 



APIHANSeneNT OF AN ICE PLANX 




FIGURE 378 



^?^r^-^ 




it 5^ 



/ 





I 



Ice Making 897 



In order to obtain absolutely pure and crystal ice by 
this system, a complete distilling and filtering process 
must be employed. Water, when evaporated into steam, 
parts with all of its impurities; the steam is condensed, 
the water of condensation being entirely pure. All the 
air must then be expelled from it, as otherwise it will 
freeze into opaque or so-called "snow^^ ice. 

The inserted illustration. Fig. 378, shows an arrange- 
ment for the production of can ice from distilled water. 
The compression and condensation of the ammonia is 
carried on as already described, the ammonia being ex- 
panded in expansion coils placed in the freezing tank. 
(18.) 

The steam generated in the boiler is first used to drive 
the steam-engine. The exhaust steam then passes to the 
steam condenser (10), first passing through an oil ex- 
tractor (9), where any lubricating matter which has been 
carried along from the cylinder is removed. The steam 
condenser is designed on the same principle as the am- 
monia condenser, being a series of pipes over which cool- 
ing water is allowed to flow. The exhaust steam is not 
usually sufficient to make the full capacity of ice, and 
sufficient live steam is therefore supplied to the steam 
condenser to make up the deficiency. The water result- 
ing from the condensing of the steam passes to the skim- 
mer (11), where any oil that may pass the oil extractor 
is removed. 

From the skimmer the water goes to the re-boiler (12), 
at the bottom of which is placed a small steam coil by 
means of which the water is kept boiling and the air con- 
tained in it expelled. . It then passes to the flat cooler 
(13), an apparatus similar to a condenser, where its tem- 
perature is reduced to that of the cooling water available. 



i.<ita 



898 Steam Engineering 

Thence it is led to the filters (14), which are furnished 
in duplicate so that one may be shnt off and cleaned with- 
out interfering with the operation of the plant. In 
special cases, where the nature of the water requires it, 
sponge, silicate, or bone charcoal filters are used. Prom 
the filters the water passes to the cold-water storage tank 
(15), which contains an ammonia expansion coil. By the 
use of the coil the distilled water is reduced to the freez- 
ing temperature before going into the freezing cans. 

By means of a can filler (17), so arranged that the 
water is automatically shut off when the can is filled 
to the proper depth, the galvanized iron freezing cans are 
filled with distilled water from the cold-water tank. The 
freezing tank (18) is usually niade of iron or steel and 
thoroughly insulated at the bottom and sides. It is pro- 
vided with suitable hardwood frame and covers, and has 
an efficient agitating device for keeping the brine in mo- 
tion. The brine acts as a medium for the transfer of 
the heat from the distilled water within the cans to the 
expanding ammonia in the expansion coils, which are 
placed longitudinally of the tank and between which the 
cans are inserted. 

The ice when frozen is hoisted out of the tank by 
means of the hoisting apparatus (19). The ice is 
loosened from the cans by the use of warm water from 
the condenser, either by employing a sprinkling apparatus 
(20) or by dipping the can bodily into a tank. 

Table 47 gives the number of cubic feet of ammonia 
gas required per minute per ton of refrigeration in twenty- 
four hours: 



Ice Making 



899 



Table 47 

cubic feet of gas that must be pumped per minute at 

different condenser and suction pressures, to 

produce one ton of refrigeration 

in twenty-four hours. 



en 

03 
O 


oTh^* 




Temperature 


of the Gas 


in Degrees 


F. 






o a. 


C5° 


70° 


75" 


80° 


85° 


90° 


95° 


100^ 


105'' 






Correspondin 


g Condenser 


Pressure (gauge), 






^ O CO 






pounds per square inch. 










103 


115 


127 


139 


153 


168 


184 


200 


218 


H 






















G. Pres. 




















—27 


1 


7.22 


7.3 


7.37 


7.46 


7.54 


7.62 


7.70 


7.79 


7.88 


—20 


4 


5.84 


5.9 


5.96 


6.03 


6.09 


6.16 


6.23 


6.30 


6.43 


—15 


6 


5.35 


5.4 


5.46 


5.52 


5.58 


5.64 


5.70 


5.77 


5.83 


—10 


9 


4.66 


4.73 


4.76 


4.81 


4.86 


4.91 


4.97 


5.05 


5.08 


— 5 


13 


4.09 


4.12 


4.17 


4.21 


4.25 


4.30 


4.35 


4.40 


4.44 





16 


3.59 


3.63 


3.66 


3.70 


3.74 


3.78 


3.83 


3.87 


3.91 


5 


20 


3.20 


3.24 


3.27 


3.30 


3.34 


3.38 


3.41 


3.45 


3.49 


10 


24 


2.87 


2.9 


2.93 


2.96 


2.99 


3.02 


3.06 


3.09 


3.12 


15 


28 


2.59 


2.61 


2.65 


2.68 


2.71 


2.73 


2.76 


2.80 


2.82 


.20 


33 


2.31 


2.34 


2.36 


2.38 


2.41 


2.44 


2.46 


2.49 


2.51 


25 


39 


2.06 


2.08 


2.10 


2.12 


2.15 


2.17 


2.20 


2 '^'2 


2.24 


30 


45 


1.85 


1.87 


1.89 


1.91 


1.93 


1.95 


1.97 


2:60 


2.01 


35 


51 


1.70 


1.72 


1.74 


1.76 


1.77 


1.79 


1.81 


1.83 


1.85 



Absorption Process. Besides ammonia, there are various 
otlier refrigerating agents employed in the compression 
system, among which may be mentioned ether, methyl- 
chloride, snlphnrons acid, and ca.rbonic acid, but space will 
not permit a further discussion of the compression system, 
and the absorption process will now be taken up. 

The principle involved in the operation of apparatus 
for the abstraction of heat by the evaporation of a sepa- 
rate refrigerating agent of a volatile nature under the 
direct action of heat, and without the use of power, which 
agent again enters into solution with a liquid, is, more 
1 a chemical, or physical action than a mechanical one. It 
iis founded upon the fact of the great capacity possessed 
by water for absorbing a number of vapors having low 



900 Steam Engineering 

boiling points, and of their being readily separable there- 
from again, by heating the combined liquid; hence it is 
commonly known as the absorption process. 

The absorption process was invented by Ferdinand 
Carre about the year 1850. This system involves the 
continuous distillation of ammoniacal liquor, and requires 
the use of three distinct sets of appliances, viz. : 

First, for distilling, condensing and liquefying the am- 
monia. Second, for producing cold, by means of a re- 
frigerator, and absorber, a condenser, a concentrator and 
a rectifier. Third, pumps for forcing the liquor from 
the condenser into the generator for redistillation. The 
three operations are each distinct from the other, but 
v/hen the apparatus is in actual work they must be con- 
tinuous, and are dependent upon one another, forming 
separate stages of a closed cycle. 

An advantage of the absorption process is that the bulk 
of the heat required for performing the work is applied 
direct without being transformed into mechanical power. 
The first machines, however, constructed upon this prin- 
ciple were very imperfect in operation, by reason of the 
impossibility of securing an anhydrous product of dis- 
tillation, and as the ammonia distilled over contained as 
much as 25 per cent of water, a very large expenditure of 
heat was required for evaporation, and the working of 
the apparatus, moreover, was rendered intermittent. This 
was owing to the distillation, which is the most important 
operation, and has of necessity to be executed in a rapid 
manner, being, in the first machines, very imperfectly ef- 
fected, and the liquor resulting therefrom being naturally 
much diluted with water. Another serious result of the 
above defect was the accumulation of weak liquor in the 



Absorption System 



901 



i 



s 

H 

M 

I 



M 



o 



o 

w 

H 
O 







902 Steam Engineering 

refrigerator^ and the consequent necessity for constant ad- 
ditions of ammonia. 

Fig. 379 illustrates an ammonia absorption^ refrigerat- 
ing device^ one of a leading American type^, and will give 
a clear idea of the operation in general of the system. 

A constant pressure of about 150 lbs. per square inch 
is maintained in the generator^ and to prevent this pres- 
sure from being exceeded^ a safety valve is provided on 
the dome o.' the generator. The gas that escapes through 
this safety valve is led through a suitable pipe to a small 
water tank^ where it is absorbed. The operation is as 
follows : 

The aqua ammonia is first introduced into the genera- 
tor, the gas or vapor expelled therefrom by heat into 
the condenser; and^ so that the process may be carried out 
continuously and not be arrested by the exhaustion of the 
solution, the exhausted or impoverished liquor is slowly 
drawn off at the bottom of the generator, an equal vol- 
ume of fresh strong solution being constantly inserted 
at the top thereof. The united effects of the cooling and 
pressure produce liquefaction of the ammoniacal gas or 
vapor in the condenser, and the liquid ammonia passes 
to the refrigerator. It will be seen that the ammoniacal 
gas or vapor from the tubes of the refrigerator is re- 
absorbed, and a rich solution is formed to feed the gen- | j 
erator, the absorbing water used being that withdrawn 
exhausted from the latter. Thus the generator and the 
.condenser will keep up a continuous supply of the liquid, 
and the refrigerator will continue to freeze successive 
charges of water in the ice-cans or cases, provided, how- 
ever, that the requisite heat to vaporize or gasify the am- 
monia is supplied to the generator. If, therefore, the 
entire apparatus be perfectly fluid-tight, as it is theo- 



Absorption System 903 

retically supposed to be^ no escape conid take place by 
leakage or otherwise, and the same materials would go 
on indefinitely producing the same uniform effect. 

In starting a machine constructed on the absorption 
principle it must be first blown through to expel all the 
air. In Carre's apparatus the air escaping from the ab- 
sorber is conducted by a suitable pipe into what is known 
as a purger, where it is passed below the surface of water 
to absorb or retain any ammonia that would otherwise 
escape with the air. 

A large amount of water is required for cooling pur- 
poses in the condenser or liquefier, and absorber, and a 
considerable consumption of fuel is also necessary to heat 
the generator, when this is performed directly by means 
of a furnace. When, however, this is effected by steam- 
heated pipes, or, by coils of pipe heated by the exhaust 
steam from an engine, or even by direct or live steam 
from a boiler, there is a considerable saving on this head. 
Steam or other motive power is likewise required for 
driving the force pump. 

The operation of Eeece's improved apparatus is briefly 
as follows: 

The charge of liquid ammonia (the ordinary commer- 
cial quality of a density of 26° Beaume) is vaporized by 
the application of heat, and the mixed vapor of water 
; and ammonia passed to the vessels called the analyzer, 
and the rectifier, wherein the bulk of the water is con- 
idensed at a comparatively high temperature, and is re- 
) turned to the generator. The ammoniacal vapor or gas is 
ithen passed to the condenser, where it is treated in a 
substantially similar manner to that in Carre's apparatus, 
'that is to say, it is caused to liquefy under the combined 
action of the condensation effected by the cooling water 



904 Steam Engineering 

circulating around the condenser tubes^ and of the pres- 
sure maintained in the generator. The liquid ammonia 
(in this case practically anhydrous) is then used in the 
refrigerator, and the vapor therefrom, whilst still under 
considerable tension, is admitted from the refrigerator to 
a cylinder fitted with a slide valve, and entry and ex- 
haust ports, practically similar to those of a high pressure 
steam-engine, and is thus utilized to drive the force pump 
for returning the strong solution to the generator, after 
which it is passed into the absorber, where it meets, and 
is taken up by, the weak liquor from the generator, and 
the strong liquor so formed is forced back into the gen- 
erator by means of a force pump. 

The important features of the absorption machine are 
the expansion valve, the absorber and the strength of the 
liquor. The expansion valve should be handled very care- 
fully, as it is delicate and will not bear rough usage. 

The expansion valve may be likened to a throttle valve 
on a full-stroke engine. If opened wide, or more than is 
necessary to operate the machine a little above its ca- 
pacity, it will draw on the generator as a wide-open pipe 
will draw on a boiler, and it will take from the generator 
more liquor than can be separated in the rectifier; and 
when it passes the rectifier it must go through into the 
cooler. As this liquor cannot evaporate at that tempera- 
ture, it will plug up the cooler. This is termed a "boil- 
over.'^ 

Shutting off the gas valve also necessitates shutting off 
the expansion valve and the machine stops working, with 
the consequent raising of temperatures. Also, when the : 
machine is purged and the gas and expansion valves are ,? 
opened, 10 or 12 degrees in temperature will be lost, as it jpf 
will be an hour or more before the machine gets to work Ilia] 



Absorption System 905 

reducing temperatures again^ and if there is still bad 
liquor in the condenser^ to come over, the machine will 
want purging again soon, with another rise in tempera- 
ture. 

The Absorber, The efficiency of the machine depends 
upon the condition of the absorber. If the absorber is 
cool, and free from air or poor gas, the cooler will give 
off its gas with ease. As long as the water and absorber 
are cool, it is difficult to know about the spray at the 
top. This spray device is simply a valve with three oblique 
holes. 

If one side of the absorber gets warmer than the other, 
the valve should be turned down slightly, say one-eighth 
of a turn, and by a little manipulation the temperature 
of the entire absorber may be evenly maintained. If a 
small scale, or dirt should get over a hole,' it will close 
that much of the valve. This valve does not regulate the 
flow of the poor liquor, but rather its distribution over the 
coils. The flow of the poor liquor is regulated by the 
valve near the exchanger, that at the generator being used 
only to shut off the poor liquor entirely. There should 
be Just sufficient poor liquor thrown over to absorb the 
gas. More than this puts> an extra load on the ammonia 
pump, exchanger and absorber. 

At this point is where the expense of the absorption 
machine comes to be considered, as regards water, and also 
the capacity of the machine, the whole being limited by 
the amount of gas the absorber will take over from the 
cooler. When the absorber is cold, the poor liquor within 
it will have a large absorbing capacity, and it will take 
;gas from the cooler even if it is gas of medium high 
percentage, but if the absorber becomes warmer, it will 
have less absorbing power, and do less work. If the tem- 



906 Steam Engineering 

perature cannot be improved because of insufficient water, 
then the liquor coming over should be made weaker by 
turning more heat on the generator, and distilling more 
of the gas over into the condenser, which will carry a 
larger amount in storage. Under these conditions, the 
cooler will also need more gas, and this will tend to 
weaken the whole charge in the generator, thus requir- 
ing a higher temperature in the coils, and a higher pres- 
sure to distill the necessary gas from the weakened charge. 

With the cooling water at a temperature of 60° or lower, 
a low pressure machine will operate at atmospheric pres- 
sure. With the water at 70°, the steam pressure may have 
to be raised two or three pounds; and if the temperature 
of the water is 75°, the pressure will need to be increased 
to 10 pounds. The pressures required depend upon the 
amount of heating surface in the generator. With water 
at a temperature of 60° the pressure in the generator may 
be from 90 to 100 pounds; but with the water at 75°, it 
will be necessary to carry generator pressure at 150 to 160 
pounds. 

It is possible to ascertain at any time whether or not 
the absorber is taking hold well, by observing the frost on 
the gas pipe. If this frost continues white, and keeps on 
accumulating, it is an indication that the absorber is 
working uniformly. If the frost begins to thaw, either 
the absorber has let go, or the cooler has become fouL ■ 
The pipe at the bottom of the absorber should have a swivel 
joint, thus making it possible to swing it into or out of 
a pail of water. This is for the purpose of testing for 
the presence of air in the system. To make a test, place 
a bucket of cold water under the outlet, and open the 
valve one-eighth or one-quarter turn. If air is present, 
bubbles will rise to the surface of the water vfithout noise. 



% 



Absorption System 907 

Should there be but few bubbles^ accompanied by a crack- 
ling sound similar to that made by water into which steam 
is being blown^ it indicates the presence of gas, showing 
that this portion of the machine is all right. If, when air 
bubbles are rising, a lighted match be held over the pail 
of water and a pale yellow flame results, it shows that 
there is some foul gas mixed with air. 

Half way up the absorber there is another purge pipe 
for drawing off foul gas. If this valve is slightly opened 
and the gas issuing therefrom is lighted, and continues to 
burn of itself, it shows foul gas, and the pipe should be 
turned into a pail of water until good gas comes, which 
can be told by the crackling sound. Do not make the 
mistake of holding a light under it only to light it. Am- 
monia gaa will burn (if a light is kept under it) with a 
very similar flame. The pail of water tells the story. 

There should be sufficient anhydrous ammonia in the 
system for the cooler to have all it wants, and allow the 
generator to keep a few inches in the condenser gage all 
the time, with the steam pressure down to the low point. 
This is with a cool absoAer, and it is sometimes possible 
to have the liquor in a cool absorber so rich that the pump 
will not take it, the gas separating out in the pump, a 
condition which will be shown in the glass gage of the 
absorber, as when the pump lets go, the absorber fills up, 
and the liquor in the glass will effervesce like soda water. 
The remedy is to weaken the charge by throwing more of 
the gas over into the condenser, for a reservoir, and start 
the pump by pressure from the condenser. 

The Generator. The coils for steam in the generator 
'50 in at about the center, and return near the bottom. 
When starting up a generator cold, do so easily, taking 
olenty of liriie. If possible, the better plan is to turn 



908 Steam Engineering 

steam on at the bottom and let it work its way upward. 
If it is a large machine with a flange joint in the center, 
by turning steam on strong at the top, the top will be 
heated, and expand and open the joint at the bottom. 
Should this occur, stop the heat and let it cool. Take off 
one nut at a time, oil it and put it back and pull it up 
tight. This may stop it once or twice, only do not hurry 
the heating of the generator. 

As soon as there is sufficient pressure to raise the liquor 
over through the weak-liquor pipe, open the valve and 
when the liquor shows in the absorber start the pump. 
This sets up a circulation in the generator and the danger 
is over. When the pressure is shown to be sufficient to 
liquefy the gas, which will be at 70 pounds, and it does 
not show on the gage in the condenser, open the expan- 
sion valve slightly so as to start circulation. The top 
of the steam coils is about at the center of the generator. 

It is a good plan to make a gage from a pine strip 
marked in inches and half inches and fasten it to the 
gage fittings, with a mark showing the top of the coils. 
The charge in, the generator should always be kept above 
the coils and usually near the top of the generator. This 
level will change, depending on the gas in the condenser 
aiid cooler, and the liquor in the absorber. Sometimes, 
purging the cooler will raise the level in the generator 
4 or 5 inches. When a lot of the anhydrous ammonia is 
sent over into the condenser the level will be changed. 

If there is no leakage around the ammonia pump, all 
loss will be of anhydrous ammonia, and it must be re- 
plenished with the same. Should there be leakage of 
liquor, it can be replenished with aqua ammonia, or with 
water and anhydrous ammonia. If water is used, it should 



'to 



Absorption System 909 

be pure, distilled water, as impure water would cause foul 
gases. 

The troubles caused by allowing the charge to get below 
the generating coils are two: If allowed for more than a 
short time the ammonia will corrode the pipes, and the 
hot pipes in the gas will decompose the gas. This will 
be shown up around the cooler, the frost everywhere being 
excessively heavy, as though everything was frozen up, and 
the gage on the absorber will show about as good vacuum 
as a condensing engine. The temperature of the brine 
will be high, as that is the only thing that does not show 
any low temperatures. The only remedy is a good charge 
of anhydrous ammonia and purging out the bad gas. 

Rectifier. The rectifier is for drying out the gas and 
should be run cool enough to chill off the moisture but not 
cool enough to liquefy the gas, or any portion of it, as it 
would drain back into the generator and have to be dis- 
tilled again. The last passage of water is through this 
vessel, and there is a bypass around it for the water so 
that the temperature can be regulated. There are ther- 
mometers for the rectifier, and water leaving it. 

If considerable water is used because of the absorber, 
a large amount will go through the bypass. If water is 
economized and the absorber is warm, all of it may go 
through the rectifier. The thermometer should not register 
below 110°. The drain pipe should feel warm to the 
hand. 

Dirty Coils, The condenser and absorber coils are liable 
to the same trouble where the water becomes warm and 
the flow sluggish. Corrosion, in the form of "barnacles^' 
sets in, and the pipes gradually become filled. These coils 
have headers at both top and bottom and each coil has a 
valve at both ends. 



910 . Steam Engineering 

There should be an air compressor on the premises 
capable of maintaining a pressure of 80 pounds through 
an open %-inch pipe. The headers should be connected 
to the air line, and also to a water pressure, with %-inch 
pipe; the feed line will do. 

Once a week the ammonia should be shut off, or rather, 
the machine should be stopped and the water drawn from 
the coils, the bottom valves closed, and air turned on. 
There should be a valve for the bottom header, in the 
bottom of the flange, which should be opened, and then 
the valves on the coils should be opened separately and 
the air allowed to blow through. The deposit will be soft 
and will easily clear out. After air has blown through, 
turn on the water in the same manner and wash the coils 
out. While the machine is idle, the brine temperature 
may have gone up one or two degrees, but it will readily i 
come down again. 

If the coils are badly coated the machine will have to be 
stopped for two or three days. The ammonia will have to 
be drawn from the condenser and absorber, as if warmed 
up the expansion would cause too much pressure. In 
drawing off the ammonia be careful not to reduce it too 
low all at once, or the freezing effect will be so great 
as to freeze the water coils. 

Have prepared a sufficient quantity of a strong potash 
solution, draw the water from the coils, fill them with 
potash and let it stand for twenty-four hours, or longer 
if the machine can be spared. When the potash is drawn 
off, turn on the water from the small cleaning pipe and 
fill the coils. Close the valve to within one-half turn and 
turn on the air. Open one valve at the bottom of the 
coil header and keep it open until the water runs clear, 
then close that one and open another. After all have been 



k 



Absorption System 911 

blown^ begin with the first and go over them again. They 
may require four or five blowings out before they will be 
clean. 

When air and water issue from a pipe together^ it will be 
noticed that it issues with a series of explosions, which 
appear to take place all through the coil and may be 
thought to do the cleaning, but this method has little 
effect without the potash. Water at from 125 to 150 de- 
grees appears to do better work than cold water, as the 
vapor from the warm water makes the explosions stronger. 

Brine. — For brine, chloride of calcium should be used 
instead of chloride of sodium, because it cleans the pipes 
better, prevents corrosion, and will carry lower tempera- 
tures. Care should be taken to get the purest, but even 
with this there is a sludge that will stop circulation in 
small pipes, and sometimes in good-sized pipes. Place a 
steam pipe in the tank for dissolving purposes and do 
not fill the tank full of water after the calcium is placed 
in it. When the mixing tank is charged, turn on steam 
until the tank boils, then close the steam valve. Skim 
oft' the scum that rises. It will be necessary to wait until 
the brine cools before pumping it into the system, other- 
wise it would raise temperatures. The skimming can be 
done without heating, but not as much of the impurities 
will rise as by heating, and not much time is gained, as 
the dissolving is so much slower. Heating saves lots of 
'cleaning later, also. 

Danger in Ammonia Fumes. — In case of accident, am- 

tfmonia is a bad thing, as it takes but a small amount to 

overcome a person. Acetic acid is an antidote and is 

-found in ordinary vinegar. A sponge soaked in vinegar 

it,|and put over the nose will enable anyone to work in a 

eB Pstrongly impregnated atmosphere, as far as breathing is 



41 



912 Steam Engineering 

concerned, but the eyes would not be protected. To work 
under such conditions it is necessary to wear a helmet, 
which should be kept charged at all times at 125 pounds 
pressure and regulated so that it will take one-half hour 
io reduce the pressure to 25 pounds. 

Should anyone be in danger of suffocation, breathing 
the fumes from vinegar will neutralize it. Drinking warm 
milk will relieve a person partly suffocated from ammonia 
or any gas. 

Workers around ammonia should not forget the strong 
aflRnity it has for water and the absorbing power of water. 
When there is a small leak of even the gas under pres- 
sure, a piece of water-soaked waste put over it will remove 
all trouble until the water is thoroughly saturated with it. 

It is a good idea to practice using water for even unim- 
portant leaks so as to be accustomed to it. A 1-inch hose 
and a 2%-inch hose under water pressure should always 
be handy, as by their use a big leak could be drowned; 
and these would be thought of instantly if one were ac- 
customed to the use of water to take care of ammonia 
fumes. 

There are various devices for detecting leaks, but the 
best is white litmus paper. This can be procured free 
from the dealer in ammonia. Take a strip i4:-iiich wide 
and about 1% inches long. With a thread, tie it onto a 
small stick 15 to 18 inches long. When using it, moisten 
it in water and hold it to the suspected place. Tf there 
is a leak the paper will turn red and the shade of red 
ivill show how strong the leak is. Litmus paper will de- 
tect leaks that cannot be smelled. Turn it away from the 
leak into pure air and it again becomes white. It can 
he used until completely worn out, all that is necessary, 
^hen using it, being to moisten it. 



k 



I 



»i!il 



At sorption System 913 

For putting screwed fittings together^ or for material 
to put on flanges^ use litharge and glycerine; for sheet 
packing, use pure rubber. Do not get fittings intended 
simply to receive the pipe that is to be screwed into 
them ; get special ammonia extra-heavy fittings, either with 
a stufiing-box at each end of the fitting, in which rubber 
packing should be used or fittings with a lead ring in 
each outlet, and with provision to put in shot and allow 
a plug to be screwed in the top to force the shot down 
on the pipe. 

Weak-liquor Pipe, — In regard to the weak-liquor pipe, it 
should be remembered that as the pressure in the genera- 
tor is carried higher the flow through this line is increased 
unless throttled. 

Charging^-^When charging a new compression system, 
proceed as follows: 

Make a proper connection between the outlet valve of 
the flask and the manifold where there are three valves. 
After creating a vacuum in the system close the right 
hand valve and open the other two. Carefully open the 
valve on the flask and the pressure will force the am- 
monia into the system, where it will expand and destroy 
the vacuum. To prevent this as much as possible use 
plenty of water on the condensers. Start up the compres- 
sor and run it slowly .until all of the ammonia is out of 
the flask, when the bottom of it will begin to freeze. Care 
should be taken to have the outlet valve at the lowest part 
of the flask. Eun the compressor until the back pressure 
gauge indicates zero, close the two valves used to admit 
the ammonia, and let the machine stand for about 15 
pinutes, before changing any of the valves on the system. 

With the absorption system there is no compressor with 
which to create a vacuum in the pipes, but if the whole 



914 Steam Engineering 

system is filled with steam before it is used at all, it will 
drive out the aii^, then by using water on the condenser 
and in the brine tank, this steam may be condensed and 
a vacuum formed for testing, as with the compression 
system. A light steam pressure will answer every pur- 
pose in this case. The absence of a pump also prevents 
the high pressure air test. 

When charging the absorption system a partial vacuum 
may be secured as already described, when the pressure 
in the ammonia flask will cause the contents to escape 
into the system. Ammonia flasks should be weighed both 
before and after charging, so that the amount used may 
be definitely known. It is a good plan to test ammonia 
before putting it into a system, by drawing a small quan- 
tity of it out of the flask and, seeing that it will evaporate 
without leaving any sediment. 

Starting, — When starting a compression system, open 
the regulating valve on the discharge pipe slightly at first, 
but do not allow the compressor to pump a vacuum on 
the coils, for the regulating valve should be open until 
there is perhaps 15 pounds back pressure, although there 
is no cast-iron rule for this purpose. It is well to cal- 
culate on about one-tenth of the high pressure, for the 
low or suction pressure side, so that if 200 pounds is 
carried on one, about 20 pounds will be right for the 
other. This is one of the many points that each engineer 
must decide for himself, for it will depend on circum- 
stances. When the brine is warm, a high pressure on 
the condenser side is advisable, so that the full benefits 
of expansion may be secured, but if the brine is cooler, it 
is evident that a lower pressure will answer the purpose. 
High pressures are expensive, as it requires more steam 
to pump against them, and this should be taken into ac- 



Absorption System 915 

count, for there is no necessity of freezing the suction pipe 
back into the engine room, where the heat will cause water 
to drop on the machinery and the floor. When frost shows 
on the suction pipe just beyond the brine tank, or just out- 
side of whatever room is to be cooled, it shows that the 
best results are secured. 

In some cases, however, where a double-acting compres- 
sor is in use, it may become necessary to freeze back to 
the compressor in order to prevent undue accumulation of 
heat in the cylinder which would cause the machine to 
work at a disadvantage, and might burn out the fibrous 
packing around the rod, or injure the metallic packing, if 
such is used. On the other hand if the frost reaches back 
to the cylinder of a single-acting compressor, it may do 
much damage by freezing up the packing, so that here, as 
elsewhere about a refrigerating plant, much depends upon 
the good judgment of the engineer. 

When running with wet compression, the discharge pipe 
should never get very warm, but with dry compression it 
may be hot enough to burn the hand, without doing any 
damage. 

■I If trouble is encountered in keeping the stuffing-boxes 

' tight on a vertical single-acting compressor, it may be due 

to the presence of weak liquor on the cylinder head, which 

'flows down the piston rod, and causes an unpleasant odor 

to fill the room. If the glands are tightened up to stop 

it, the rods may be scored and badly damaged. 

The safest method is to take the packing out, and allow 

this weak liquor to run out, and if there is a collar next 

iM'to the rod, it may be necessary to take out the piston 

.and sponge the liquor out, as the collar will prevent it 

iffljfrom running out. Care must be taken to prevent oil 

aC' from passing the oil separator. The oil should be purged 



916 Steam Engineering 

out and not allowed to pass over into the coils where it 
is not wanted. If it does get into them, it is necessary to 
disconnect the pipes and blow live steam through them 
until it is all driven out. If they are badly coated, it 
may be necessary to clean them out with a solution of 
soda ash, and then blow steam through them, and after- 
wards air under pressure, to purify them. 

Whenever a serious leak develops on the high pressure 
side of the apparatus, the valves must be so manipulated 
that the ammonia will be drawn from this side over into 
the suction side, while the compressor is run at a slow 
speed, when the proper valves should be shut to keep it 
locked up there until the repairs are completed. If the 
leak is on the suction side, the liquid valve must be closed 
and all of the ammonia pumped up into the condenser, 
then by closing the valve on the top of the condenser it 
may be retained there until the machine is again ready 
for use. Incompetent men in charge of these machines, 
have been known to allow all of the ammonia to escape 
into the air, when there was a leak in the pipes, to the 
extreme disgust of the neighbors, and the detriment of 
the owners, but in a majority of cases this is entirely 
unnecessary. 

When it is time to shut down a machine of this kind, 
the liquid valve should be closed, and the suction pres- 
sure reduced to zero. Do not pump a vacuum at this 
time, for it may cause the system to be filled with air 
before starting up again. 

Properties of Ammonia. — Ammonia is composed of one 
part of nitrogen and three parts of hydrogen, represented 
by the formula NH3. It is a colorless gas, possessing a 
pungent odor. It is much lighter than air, having a 
specific gravity of 0.58, that of air being 1. 



lal 






Properties of Ammonia 917 

It can be obtained from the air, from sal ammoniac, 
nitrogenous constituents of plants and animals bj^ process 
of distillation ; as a matter of fact, there are very few sub- 
stances free from it. 

Ammonia in itself is a slight lubricant, and has no effect 
whatsoever on iron or steel, of which ice machinery is con- 
structed. It will eventually purge and scour the entire 
system clean to the metal surfaces, the loose foreign matter 
being caught in the separators and interceptors provided 
for this purpose. 

At the present day almost all the sal ammoniac and 
ammonia liquors are prepared from ammoniacal liquid a 
by-product obtained in the manufacture of coal gas and 
coke. Although ordinarily existing as a gas, it may be 
condensed to a liquid by cooling, and applying pressure. 
Liquid anhydrous ammonia formed in this way boils under 
atmospheric pressure at 28.5 degrees below zero, and its 
latent heat of evaporation is about 562 British thermal 
units at 32 degrees P., at which temperature 1 pound of 
the liquid evaporated under atmospheric pressure will oc- 
cupy 21 cubic feet. 

Pure ammonia liquid is colorless, having a peculiar 
alkaline odor, and caustic taste. It turns red litmus paper 
blue. Compared with water, its weight or specific gravity 
at 32 degrees P. is about % of water, or 0.6364. One 
cubic foot of liquid ammonia weighs 39.73 pounds, one 
gallon weighs 5.3 pounds, one pound of the liquid 
at 32 degrees will occupy 21.017 cubic feet of space when 
'evaporated at atmospheric pressure. The specific heat of 
ammonia gas, as determined by Eegnault (capacity for 
heat), is 0.50836. Its latent heat of evaporation, as deter- 
^mined by the highest autliorities, is not far from 560 ther- 
mal units at 32 degrees, at which temperature one pound 



II 



918 



Steam Engineering 



of liquid evaporated under a pressure of fifteen pounds per 
square inch^ will occupy twenty-one cubic feet. 

Table 48 gives the properties of saturated ammonia. 



Table 48 

PROPERTIES OF SATURATED AMMONIA— (Wood). 

The critical pressure of ammonia is 115 atmospheres ; critical tempera- 
ture at 266° F. (Dewar) ; critical volume .00482 (calculated). 



Tempera- 
ture 


Pressure, 
absolute 


.2 

O tn 

ffi-S 


-a 

X % 


+1 tn 

II 


u 

O 

o. . 

> 

Ba 

> a 


■S3 

Ba 

> a 


s 


(A 

<U 

<u 
u 
to 

a 


o 

1- 

< 




.J 


en 

dxi 

4-. o 


— 40 

— 35 

— 30 


420.66 
425.66 
430.66 


1540.9 
1773.6 
2035.8 


10.59 
12.31 
14.13 


579.67 
576.69 
573.69 


48.23 
48.48 
48.77 


531.44 

528.21 
524.92 


24.37 
21.29 
18.66 


.0234 
.0236 
.0237 


.0410 
.0467 
.0535 


— 25 

— 20 

— 15 


435.66 
440.66 
445.66 


2329.5 
2657.5 
3022.5 


16.17 

18.45 
20.99 


570.68 
567.67 
564.64 


49.06 
49.38 
49.67 


521.62 
518.29 
514.97 


16.41 
14.48 
12.81 


.0238 
.0240 
.0242 


.0609 
.0690 
.0779 


— 10 

— 5 



450.66 

455.66 
460.66 


3428.0 
3877.2 
4373.5 


23.77 

25.93 
30.37 


561.61 
558.56 
555.50 


49.99 
50.31 
50.68 


511.62 

508.25 
504.82 


11.36 

10.12 

9.04 


.0243 
.0244 
.0246 


.0878 
.0988 
.1109 


+ 5 
-- 10 
-- 15 


465.66 
470.66 
475.66 


4920.5 
5522.2 
6182.4 


34.17 

38.55 
42.93 


553.43 
549.35 
546.26 


50.84 
51.13 
51.33 


501.59 
498.22 
494.93 


8.06 
7.23 
6.49 


.0247 
.0249 
.0250 


.1241 
.1384 
.1540 


-f 20 

-f 25 
-f 30 


480.66 
485.66 
490.66 


6905.3 

7695.2 
8596.0 


47.95 
53.43 
59.41 


543.15 
540.03 
536.92 


51.61 
51.80 
52.01 


491.54 

488.23 
484.91 


5.84 
5.26 
4.75 


.0252 
.0253 
.0254 


.1712 
.1901 
.2105 


-f 35 
-}- 40 
-f 45 


495.66 
500.66 
505.66 


9493.9 
10512 
11616 


65.93 
73.00 
80.66 


533.78 
530.63 
527.47 


52.22 
52.42 
52.62 


481.56 
478.21 
474.85 


4.31 
3.91 
3.56 


.0256 
.0257 
.0260 


.2320 
.2583 
.2809 


4- 50 
-- 55 
-- 60 


510.66 
515.66 
520.66 


12811 
14102 
15494 


88.96 

97.93 

107.60 


524.30 
521.12 
517.23 


52.82 
53.01 
53.21 


471.48 
468.11 
464.72 


3.25 
2.96 
2.70 


.0260 
.0260 
.0265 


.3109 
.3379 
.3704 


+ 65 
4- 70 
-f 75 


525.66 
530.66 
535.66 


16993 
18605 
20336 


118.03 
129.21 
141.25 


514.73 
511.52 

508.29 


53.38 461.35 
53.57 457.85 
53.76 454.53 


2.48 

2.27 
2.08 


.0266 
.0268 
.0270 


.40341 
.4405 

.4808 


+ 80 
— 85 
-- 90 


540.66 
545.66 
550.66 1 


22192 

24178 
26300 


154.11 

167.86 
182.8 


504.66 
501.81 
498.11 1 


53.96 450.70 
54.15 447.66 
54.28 443.83 1 


1.91 
1.77 
1.64 


.0272 
.0273 
.0274 


.5252J 
.5649 
.6098 























Properties of Ammonia 



919 



Table 48^continued 



Tempera- 
ture. 


Pressure, 
absolute. 


.2 


u 




u 


a 
^3 


"o 






O P 


^ Xfi 

gs 

u 

X 


11 


o 
'o 

> 


o 

(U ^' 

'o 

> 


^ o 


u 

Q 


6 
< 


<u . 

3" 


l-c 

3" 




+ 95 
+ 100 
+ 105 


555.66 
560.66 
565.66 


28565 
30980 
33550 


198.37 
215.14 

232.98 


495.29 
491.50 

488.72 


54.41 
54.54 
54.67 


440.88 
436.96 
434.08 


1.51 
1.39 

1.289 


.0277 
.0279 

.0281 


.6622 
.7194 

.7757 


+ 110 
--115 

-120 


570.66 
•575.66 
580.66 


36284 
39188 
42267 


251.97 
272.14 
293.49 


485.42 
482.41 
478.79 


54.78 
54.91 
55.03 


430.64 
427.40 
423.75 


1.203 
1.121 
1.041 


.0283 

.0285 
.0287 


.8312 
.8912 
.9608 


+ 125 
+ 130 
+ 135 


585.66 
590.66 
595.66 


45528 
48978 
52626 


316.16 
340.42 
365.16 


475.45 
472.11 
468.75 


55.09 
55.16 
55.22 


420.39 
416.94 
413.53 


.9699 
.9051 
.8457 


.0289 
.0291 
.0293 


1.0310 
1.1048 
1.1824 


+ 140 
+ 145 
+ 150 


600.66 

605.66 
610.66 


55483 
60550 
64833 


392.22 

420.49 
450.20 


465.39 

462.01 
458.62 


55.29 
55.34 
55.39 


410.09 
406.67 
402.23 


.7910 

.7408 
.6946 


.0295 
.0297 
.0299 


1.2642 
1.3497 
1.4696 


+ 155 
+ 160 
+ 165 


615.66 
620.66 
625.66 


69341 

74086 
1 79071 


481.54 
514.40 
549.04 


455.22 
451.81 
448.39 


55.43 
55.46 

55.48 


399.79 
396.35 
392.94 


.6511 

.6128 
.5765 


.0302 
.0304 
.0306 


1.5358 
1.6318 
1.7344 



Testing Anhydrous Ammonia, — It is essential that the 
purity of the liquid anhydrous ammonia, or the strength of 
the aqua ammonia solution shall be up to standard and to 
determine this point tests must be made. Aqua ammonia 
is usually guaranteed to be not less than 26 degrees Baume 
scale and its density can readily be measured with the 
hydrometer. Liquid anhydrous can be tested by the use 
of an ordinary glass testing tube 12 inches long or, if this 
cannot be had, take a piece of 1-inch pipe and cap one end. 
Securely fasten a piece of stiff wire about 12 inches long 
around the tube or pipe so that it can be held about a foot 
away from the hand and, after securing a piece of pipe 
of the same size as the cylinder valve, bend the threaded 
' end so that the pipe will stand vertical when in position on 



920 Steam Engineering 

the cylinder. Slip the test tube over the pipe almost to the 
bottom or about as far as it will go, open the cylinder 
valve gently, and draw a certain number af inches of the 
liquid into the tube, gradually withdrawing it from the 
bent pipe as it fills. When the desired amount of liquid 
ammonia has been drawn into the tube, remove it from the 
pipe and, after noting carefully the exact amount of an- 
hydrous ammonia, pour the liquid into a shallow vessel and 
set it in cold water, or on a block of ice. Under these con- 
ditions the ammonia will boil and evaporate quickly, and 
any residue remaining is the amount of moisture and im- 
purities originally in the liquid ammonia drawn into the 
tube. Dividing the amount of residue by the quantity of 
the liquid drawn into the tube and multiplying by 100 
gives the percentage of moisture and impurities. Before 
the liquid is drawn into the tube a little of the gas should 
be allowed to escape in order to purge the bent pipe. 

Hydrometers, — From among the instruments frequently 
used to ascertain the specific gravity of liquids, and by 
inference their strength, we mention those called hydro- 
meters as based on the Archimedian principle. They are 
generally made of a weighted body (usually of glass), hav- 
ing a thinner stem at the upper end provided with ^ scale 
divided into degrees. The degrees may be arbitrary, or 
show specific gravities or the strength of some particular 
liquid or solution in per cents ; in the latter case the instru- 
ment is called saccharometer, salometer, alcoholometer, 
acidometer, alkalimeter, etc., according to the liquid it is 
designed to test. Hydrometers for different liquids or pur- 
poses, provided they cover the same range of specific gravi- 
ties, may be used for either liquid when the relation their 
degrees bear to each other is known. 



Questions and Answers 921 

QUESTIONS AND ANSWERS. 

597. Of what does the process of refrigeration consist? 
Ans. In the abstraction of heat from a substance. 

598. Describe a freezing mixture that will give a tem- 
perature of 67 degrees below zero. 

Ans, A mixture of one pound of calcium chloride, and 
0.7 lbs. of snow. 

599. Upon what are the theory^ and practice of mechan- 
ical refrigeration based? 

Ans. Upon the two first laws of thermo-dynamics. 

600. What is the first of these laws? 

Ans. Mechanical energy and heat are mutually con- 
Tertible. 

601. Define the second law. 

Ans. An external agent is necessary to complete or 
bring about this transformation. 

602. Is heat generated by compression^ or by any other 
means ? 

Ans. It is not generated but developed, because there 
is a fixed amount of heat in the universe which can neither 
be increased nor diminished. 

603. "What is the result of compressing one pound of 
air at 70 degrees temperature and at atmospheric pressure, 
to one half its original volume ? 

Ans. An increase in its static pressure, also an increase 
in its temperature. 

604. In order that the higher pressure may be main- 
tained, as the temperature is reduced, what is necessary ? 

Ans. A small additional quantity of air will have to be 
forced into the compressor cylinder. 

605. If the pound of compressed air be allowed to ex- 
pand in a cylinder what will be the result ? 



922 Steam Engineering 

Ans, A portion of the heat developed by compression 
will be given up. 

606. What can be said of the mechanical work done 
by this air in its expansion? 

Ans. In amount it is exactly the same as that done upon 
it during its compression. 

607. How is the temperature of a body or substance 
reduced ? 

Ans» >By transferring more or less of the heat con- 
tained in the body to some other substance or body. 

608. What work is demanded of a refrigerating ma- 
chine ? 

Ans. To extract heat from a body^, and by the expendi- 
ture of mechanical energy to sufficiently raise the temper- 
ature of this heat to admit of its being carried away by a 
suitable external agent^ usually water. 

609. How may a refrigerating machine be defined, and 
what is its main function? 

Ans. As a heat pump^ its main function being the 
abstraction of heat from the body to be cooled, and trans- 
ferring that heat to a cooling agent. 

610. How may the various devices for refrigeration and 
ice making be classified? 

Ans. Under five principal heads. 

611. Explain the action of apparatus belonging to 
class one. 

Ans. Heat is abstracted from the body to be cooled, 
by the dissolution or liquefaction of a solid, as for instance 
the cooling of water with ice. 

612. Describe the vacuum system? 

Ans. The abstraction of heat is effected by the evapora- 
tion of a portion of the liquid to be cooled, the process 
being assisted by an air pump. 



Questions and Answers 923 

613. How is refrigeration effected in machines belong- 
ing to the third class? 

Ans. By the evaporation of a separate refrigerating 
agents which is subsequently restored to its original physi- 
cal condition by mechanical compression and cooling. 

614. Describe the fourth or absorption system. 

Ans. Heat is abstracted by the evaporation of a sepa- 
rate refrigerating agent^ under the direct action of heat^ 
which agent again enters in solution with a liquid. 

615. Describe the action of machines belonging to the 
fifth class^ known as cold air machines ? 

Ans. Air^ or other gas is first compressed^ then cooled, 
and afterwards permitted to expand while doing work. 

616. What two systems have come into general use in 
the United States? 

Ans. The ammonia compression system, and the am- 
monia absorption system. 

617. What are the three distinct stages in the com- 
pression system? 

Ans. Compression, condensation, and expansion. 

618. What is the refrigerating agent or medium used 
in the compression system ? 

Ans. Anhydrous ammonia. 

619. Of what does ammonia consist, and what is its 
chemical formula? 

Ans. One part of nitrogen, and three parts of hydro- 
!gen. Its chemical formula is NHg. 

620. Under what two conditions may gaseous ammonia 
be liquefied? 

Ans At a pressure of 128 lbs. per sq. in., and a tem- 
perature of 70° Pahr., or a pressure of 150 lbs. and a tem- 
perature of 77° Fahr. It may also be liquefied by cold if 
its temperature be reduced to 85.5° Fahr. below zero. 



924 Steam Engineering 

621. To what pressure is gaseous ammonia usually 

compressed ? 

Ans From 125 to 175 lbs. per sq. in. 

622. Of what does a compression plant consist? 

Ans. Of a high pressure system made up of a condens- 
ing coil surrounded by cooling water/ and a low pressure 
system consisting of an evaporating coil surrounded by 
brinC;, or open to the room to be cooled. 

623. What takes place during compression? 

• Ans. The latent heat of the vapor is converted into 
active, or sensible heat. 

624. How is the vapor condensed, or liquefied? 

Ans. It is forced into and through the condenser coils 
which are submerged in a body of cold water, or over which 
cold water is flowing, and the sensible heat developed dur- 
ing compression is thus transferred to the cooling water. 

625. How are the refrigerating qualities of the am- 
monia in its liquefied state utilized? 

Ans. It is allowed to pass in small quantities from the 
condenser into pipe coils placed in the rooms to be cooled, 
when it again expands into a vapor, and takes up an 
amount of heat exactly equivalent to that given up during 
condensation. 

626. After being expanded into vapor, what becomes 
of it? 

Ans. It is drawn back into the compressor, again com- 
pressed, condensed, and expanded, the cycle of operationsl 
being repeated indefinitely. 

627. How many, and what are the systems of refrigera- 
tion by compression? 

Ans. Two — the wet system, and the dry. 

628. Describe the theory of the wet system. 



Questions and Answers 925 

Ans. The ammonia vapor is cooled by the injection 
into the compressor Cylinder of a small quantity of liquid 
animonia at the beginning of each stroke^ and it is carried 
from the cooling room back to the compressor in a sat- 
urated state. It is thus kept in contact with a small por- 
tion of its originating fluids and is kept comparatively cool. 

629. Upon what does the pressure of steam in a boiler 
depend ? 

Ans. Upon its temperature^ which is always the same as 
that of the water in the boiler. 

630. What are the relations of temperature and pres- 
sure in the case of steam while in contact with the originat- 
ing water? 

Ans. They are interdependent. 

631. What is the result if tlie steam is superheated? 
Ans. It may still be of the same pressure^ but its tem- 
perature will be higher. 

632. What results from the compression of a dry gas 
without cooling? 

Ans Its temperature may be much higher than that 
corresponding to its pressure. 

633. What does the Adiabatic curve as traced by the 
indicator represent? 

Ans. The compression^ or expansion of a gas without 
loss or gain of heat. 

634. Describe in brief the construction ©f the cylinder 
gi heads, and valves in the Linde ice machine. 

Ans. The piston and cylinder heads are spherical, and 
;of the same radius, and the valve discs conform to this 
radius. 

635. What is the clearance between piston and cylin- 
der head ? 

Ans One thirty-second of an inch. 



926 Steam Engineering 

636. How is the piston lubricated? 

Ans. In a large measure by the 'moisture in the am- 
monia vapor. 

637. In the De La Vergne refrigerating machine how 
is the heated gas cooled ? 

Ans. By passing it through coils of pipe surrounded 
by running water. 

638. How many valves has the Triumph ice machine? 
Ans. Pive^, three suction valves^ and two discharge 

valves. 

639. What advantage is said to be gained by the use 
of the third suction valve? 

Ans. That it tends to increase the economy of the ma- 
chine. 

640. Describe the construction of a double pipe am- 
monia condenser. 

Ans. It consists of two series of coils, one within the 
other. 

641. How many methods are there of utilizing the 
brine system? 

Ans. Two; the brine system^, and the direct expansion 
system. 

642. Describe in brief the brine system. 

Ans. The coils of pipe in which the ammonia is ex- 
panded are submerged in a solution of salt, or calcium 
chloride. This brine after being reduced to a low tempera- 
ture is pumped through coils of pipe in the rooms to be 
cooled. 

643. Describe the direct expansion system.. 

Ans. The expansion coils are placed in the rooms to be 
cooled, and the cooling is effected directly by the expansion 
of the ammonia. 

644. Which one of the two systems is the most efficient?! 



Questions and Answers 927 

Ans, The direct expansion system. 

645. Mention a few of the advantages that this system 
has over the brine system. 

Ans. First — All intermediate agencies are dispensed 
with. Second — The whole plant is much simpler. Third 
— A larger expansion surface. 

646. By what two systems is ice made or manufactured? 
Ans. The can system and the plate system. 

647. Mention other refrigerating agents besides am- 
monia that may be used in the compression system ? 

Ans. Ether^ methyl-chloride^ sulphurous acid^ and car- 
bonic acid. 

648. How is refrigeration effected in the absorption 
system ? 

Ans. .By the continuous distillation of ammoniacal 
liquor. 

649. What advantage appertains to the absorption 
system ? 

Ans. The bulk of the heat required for the work is 

applied direct without being transformed into mechanical 
power. 

650'. What pressure is usually maintained in the gen- 
erator ? 

Ans. 150 lbs. per sq. in. 

651. Mention the more important features of the ab- 
sorption machine? 

Ans. The expansion valve^ the absorber, and the 
strength of the liquor. 

652. Upon what does the efficiency of the machine 
mostly depend? 

Afis. Upon the condition of the absorber. If it is cool 
and free from air, or poor gas, better results will be 
realized. 



928 Steam Engineering 

653. What should be done if one side of the absorber 
should get warmer than the other ? 

Ans, The spray valve should be turned down slightly^ 
say one-eighth of a turn. 

^654. Mention one of the troubles in the operation of 
this system. 

Ans, A filling up of the coils with scale and dirt. 

655. What is the remedy in such cases? 

Ans. Stop the machine once a week, drain the coils, and 
blow them out with compressed air. 

656. How is anhydrous ammonia formed? 

Ans. By condensing ammonia gas to a liquid, and 
applying pressure. 

657. Under atmospheric pressure, what is the boiling 
point of anhydrous ammonia? 

Ans. 28.5 degrees delow zero Pahr. 

658. What is the specific gravity of liquid ammonia 
compared with water? 

Ans. At 32^ Fahr. it is about % that of water, or 
0.6364. 

659. What is its latent heat of evaporation? 

Ans. At 32 degrees temperature it is 560 thermal- units. 

660. If evaporated at 32° Fahr. and atmospheric pres- 
sure, how much space will one pound occupy? 

Ans. Twenty-one cubic feet. 



Elevators — Electric and Hydraulic 

As the majority of stationary engineers^ especially in 
large cities and towns, have more or less to do with ele- 
vators, either electric or hydraulic, the anthor deems it 
fitting and proper that a section should be devoted to this 
subject. 

Therefore, the construction and operation of electric and 
hydraulic elevators will be taken up in order, and although 
the subject-matter will have to be somewhat condensed for 
want of space, still the leading types, including the numer- 
ous improvements which have been developed during the 
past ten years will be illustrated, and the mechanism de- 
scribed. 

OTIS TRACTION ELEVATOR. 

In the Otis traction elevator the working parts have b^een 
reduced to the simplest possible elements. The elevator 
engine, a view of which is presented in Pig. 380, consists 
essentially of a motor traction driving sheave, and a brake 
pulley, the latter enclosed with a pair of powerful springs 
actuated, electrically released brake shoes, all compactly 
grouped, and mounted on a heavy iron bed plate. 

Instead of the high speed motor used with the geared 
electric elevator, a slow speed shunt-wound motor designed 
especially for the service is used. The armature shaft 
i which is of high tensile steel, of unusually large diameter 
serves merely as a support for the load, and on it are 
mounted the brake pulley and the traction. driving sheave. 

929 



930 Steam Engineering 

The actual drive from the armature to the sheave is effect- 
ed through the engagement of projecting arms on each^ 
cushioned by rubber buffers, thus entirely eliminating all 
tortional strains to the shafts and the use of keys. In this 
machine all intermediate gearing between motor and driv- 
ing member is dispensed with, by the use of the slow speed 
motor^ and the result is, that the starting, accelerating, re- 
tarding and stopping events are each, and all, remarkably 
even and quiet. 



Fig. 3S0 

OTIS TRACTION ELEVATOR 

The driving cables, from one end of which the car i^' 
supported, while to the other end the counterweight id 
attached, pass partially around the traction driving sheave 
in lieu of a drum, continuing under an idler leading sheave 
thence again around the driving sheave, thereby forming i 
complete loop around these two sheaves, which arrange' 
ment results in the necessary tractive effort for lifting \M 
car. One of the striking advantages resulting from thii 



Electric Elevators 931 

I arrangement of cables^ and the method of driving the same 
is the decrease in traction which follows the striking on the 
bottom of the shaft of either the car or the counterweight^ 
and the consequent minimizing of the lifting power of the 

j machine, until normal conditions are resumed. Inasmuch 
as in any properly constructed elevator the parts are so 
arranged that the member (car or counterweight) which 
is at the bottom of the shaft must strike and come to rest 
before the other member can possibly come in contact with 
the overhead work, it will readily be seen that the above 
mentioned decrease in tractive effort is a valuable, and 
effective safety feature inherent in this type of elevator. 

The controller is so designed in connection with the 
motor, that the initial retarding of the car in bringing the 
same to stop is independent of the brake, the latter being 
requisitioned to bring the car to a final positive stop and to 
hold it at the landings. 

The motor is also governed in such a way, electricalh^, as 
to prevent its attaining any excessive speed with the car no 
.matter what the load in same may be. 

In designing the controlling equipment, one of the fea- 
tures demanding greatest consideration, in view of the very 
high speed at which the cars run, is the automatic retard- 
ing of their speed and the final positive stopping of same, 
automatically, at the upper and lower terminals of travel. 
This result is very satisfactorily attained with the installa- 
tion, in the elevator hatchway, of two groups of switches 
located respectively at the top and bottom of the shaft, each 
a^ switch in the series being opened one after another, as the 
!' car passes, resulting in a reduction of speed until the open- 
ing of the final switch brings the car to a positive stop, 
* applying the brake. This operation is entirely independent 



932 



Steam Engineering 



of the operator in the ear and is effective even though the 
car operating device be left in the full speed position. 

Another feature of security of the greatest interest and 
importance is provided in the Otis Patented Oil Cushion 
Buffers. (See Fig. 381.) These are placed in the hoistway, 
one under the car and one under the counterweight, and 




Fig. 381 
otis patented spring return oil buffer 

are arranged to bring either the car or the counterweight to 
a positive stop^ through the telescoping of the buffer — this 
occurring at a carefully calculated rate of speedy, which is 
regulated by the escape of oil from one chamber of the 
buffer to another. The buffers have been proven capable 
by test of bringing a loaded car safely to rest from full 



Electric Elevators 



933 



gpeed^ and in this respect are unique among elevator safety 
features of comparatively low cost. 

The usual safety devices installed in connection with 
modern high grade apparatus are used with this type of 
elevator^ including speed governors^ wedge clamp safety 
devices for gripping the rails in case of the car attaining 
excessive speedy and potential switches. 



OTIS GEARED TRACTION ELEVATOR. 

The modern adaptation^ in the Otis Traction Elevator, of 
the traction principle for elevator service which utilizes 
the patented feature of operating the car by means of driv- 




FiG. 382 

OTIS DIRECT CURRENT TRACTION MACHINE FOR OVERHEAD INSTAL- 
LATION 

ing the cables direct from the motor without the interven- 
tion of retarding rigging, showed so conclusively the merits 
of that principle that the question naturally arose as to the 



I 



934 Steam Engineering 

feasibility of employing this method of drive in the low 
speed machines as well. The result was the introduction 
of what is commercially known as the Otis Geared Trac- 
tion Elevator which embodies many of the good points of 
its larger contemiporary. 

It might be well to state here that the traction principle 
is neither new nor experimental^ as* is instanced by its use 
in the familiar type of carriage hoist, this being in reality 
a low duty hand power traction elevator driven by means 
of a hemp rope; also this method of drive has been em- 
ployed on dumb-waiters for some time. However^ as ap- 
plied to the high speed passenger machines used in our tall 
office buildings^ it must be referred to as a comparatively 
new and improved development of former types. 

The Geared Traction machine is similar in appearance 
to the standard drum machine, except that a multi-grooved 
driving sheave is mounted in place of the drum^ and a non- 
vibrating idler leading sheave takes the place of the vibrat- 
ing sheave necessary on the drum type. The car and the 
counterbalance weight hang directly from the driving 
sheave — one from either end of the cables — in precisely the 
same manner as with the Otis Traction Elevator ; the neces- 
sary amount of traction being obtained by the extra turn 
resulting from passing around the idler sheave. 

The machines are built in two classes, double screw^ and 
single screw, depending upon the duty required. 

The double screw machine is designed for the heavier 
duties^ and the gearing consists of a right and left hand 
worm, see Fig. 383, accurately cut from a solid forging. 
This worm, coupled directly to the electric motor, runs 
submerged in oil and meshes with two large bronze gear 
wheels, which in turn mesh with each other. The effect of 
the three-point drive thus obtained, in conjunction with 



Electric Elevators 



935 



the right and left hand thready is the entire elimination of 
end thrust on the worm shaft — a most desirable feature, 
i The complete gear is fully protected in an oil tight iron 
case and is well lubricated in every part. 

To the forward gear wheels that is the one furthest from 
the motor^, there is bolted the iron buffer-neck^ or what 
might be termed the driving spider. It is constructed in 
such a way that the use of keys is unnecessary to effect the 
drive^ inasmuch, as the flange of the buffer-neck is bolted 
with through bolts directly to the bronze gear wheel near 




I 



Fig. 383 
theee point drive 



its periphery^ and by means of four extending arms on its 
opposite end engages with similar arms on the driving 
sheave. A mechanically strong and perfect drive is thus 
obtained. The shaft passing through the driving sheave 
and buffer-neck serves merely as a support for the moving 
loads and is subject to absolutely no tortional strains. In 
order to protect the gears and elevator car from possible 
{ribrations, large rubber buffers are placed under slight 
; compression between the arms of the sheave and those of 
the buffer-neck. 



936 Steam Engineering 

The machine is equipped with a mechanically applied, 
and electrically released donble shoe brake. The shoes are 
applied against a pulley of ample diameter and width to 
dissipate any heat generated, and serves as a coupling be- 
tween the motor shaft and the worm shaft. 

The brake shoes are normally bearing against the pulley 
with a pressure corresponding to the compression of the 
two helical springs. When current is admitted to the 
solenoid brake magnet, and then only, the action of the 
springs for the time is overcome, so that the shoes are 
released. It will be seen, therefore, that the brake will 
apply with full force should a failure of current occur; 
resulting in an immediate stop of the elevator. 

The motor is compound wound, and runs at about eight 
hundred revolutions per minute at full car speed and load. 
The series field is used only at starting to obtain a highly 
saturated field in the shortest possible time, and is then 
short-circuited, leaving the motor to run as a plain shunt 
wound type. 

In stopping, a comparatively low resistance field is 
thrown across the armature, providing a dynamic brake 
action and a gentle slowing down of the car, the mechanical 
brake being called upon only to effect the final stop and to 
hold the load at rest. Eesistance in series with this "Extra 
Field,^^ as it is called, is controlled by magnets which de- 
pend, in their operation, on the speed of the armature. 
It is therefore evident that the dynamic, or retarding effect 
of the field is proportional to the speed, and therefore to 
the load in the elevator car, hence good stops under all 
conditions are easily obtained. 

To meet the demands in districts where alternating cur- 
rent is in use, the same apparatus described is furnished 






Electric Elevators 



937 



except that the direct current motor and controller give 
place to an alternating current motor and controller. 

The alternating current machines are made in two classes 
also^ single and double screw. The cut^, Fig. 384^ repre- 
sents a double screw machine designed for basement in- 




Fig. 384 

otis alternating current double screw traction machine 

Designed for Basement Installations 



stallations. The brake is slightly different in appearance 
'but performs the same functions as does the direct current 
brake. 

The safeties used on the Otis Traction Elevators are 
found on the geared traction elevators. The main differ- 
lei ^ence between the two machines being the ability to use on 



938 



Steam Engineering 



the latter a small high speed motor with gearing, instead 
of the large, slow speed and more expensive motor of the 
Otis Traction Elevator. 






^M,m^m^ 



^^pff-m 



*& 



Fig. 385 

MAGNET CONTROLLER 

Fig. 385 shows the Otis electric magnet controller, and 
Pig. 386 shows the standard car switch. With this operating 
device the current is automatically and gradually admitted 
to the motor, enabling the operator to start and stop the 
car without shock or jar. This controlling device is con- 



car 



Electric Elevators 



939 



structed to secure the motor against damage by any over- 
load, or excess of current; these features are automatic in 
their operation, are independent of the operator in the 
car, and are designed to prevent more current being ad- 
mitted to the motor than is required to do the maximum 
work of the elevator. 








Fig. 386 

OTIS LEVER CAR SWITCH 



Electro magnets are employed throughout, thereby elim- 
inating the use of all rheostats, sliding contacts, or other 
easily deranged devices. The contacts and wearing parts 
Jiin the controlling mechanism are of ample dimensions to 
rimeet the severe conditions, and exacting requirements of 
elevator operation and control. 

• Careless Operation. — The waste of power caused by the 
careless operation of electric elevators is well worth consid- 



940 Steam Engineering 

eration. The following timely suggestions are quoted from 
an article by C. M. Eipley in the September, 1909, issue of 
Power : 

^^An electric passenger elevator driven by a 30-horse- 
power motor on a 220-volt circuit is generally fused for 150 
amperes. Assuming that it requires four seconds for the 
car to gain its maximum speed, and that electric service 
costs 10 cents per kilowatt-hour, the cost of merely start- 
ing the elevator will figure out as follows : 

150X^20X4=132,000 watt-seconds; 

132,000^3600=36.6 watt-hours or 

0.0366 kilowatt hour; 

0.0366X10=0.366 cent, or over a third 

of a cent. 

^^In a building with, let us say, one elevator, serving six: 
floors continually for eight hours, this waste in power would 
be considerable if the operator had to make one unneces- 
sary start on each trip, or two unnecessary starts for each 
round trip. If this car made 84,000 round trips in a year, 
the power waste would cost over $60. And if this average 
held good in buildings with ten elevators instead of one, 
with 24-hour service instead of 8-hour service, and with 20 
stories instead of six stories, the loss would amount to 
something over $3,000. The wear and tear on switch con- 
tacts, controller contacts, controller magnets, commutator, 
armature, steel worm, bronze gear or gears, thrust plates, 
ball bearings, armature bearings, drum-shaft bearings, the 
car cables, the counterweight cables .and the back-drum 
cables are all materially increased also by increased 
starting.^^ 

Table 49 gives some interesting and instructive data 
regarding the starting and running current, fuse capacity^ 
etc., of various sized motors for Otis elevators. 



Electric Elevators 



941 




Fig. 3S7 

DOUBLE WORM AND GEAR ELECTRIC ELEVATOR, OVERHEAD INSTAL- 
LATION 



942 



Steam Engineering 



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Electric Elevators 



943 




i 



Fig. 388 
^le worm and gear electric elevator, basement instal- 



I 



LATION 



944 Steam Engineering 

In addition to the waste of power caused by unnecessary 
starts^ there is the tremendons strain to which the appar- 
atus and cables are subjected when the car is suddenly 
stopped on the down trip ; there is also the liability of 
burning out armatures by hasty reversals. Most elevator 
controllers are designed now so that the current cannot be 
sent through the motor in the reverse direction until the 
armature has ceased revolving. But there are many con- 
trollers still in use which are not so equipped^, and motors 
operated with such controllers can easily be damaged by 
suddenly reversing the car switch before the motor has 
stopped revolving. If an elevator operator reverses his 
switch to the ^^down^^ position before the motor has fully 
ceased rotating in the "^^up^^ direction^ the effective voltage 
at the armature terminals will be practically the sum of 
the line voltage and the counter electro-motive force of the 
armature^ instead of the difference between the line voltage 
and the counter electro-motive f orce^ or almost twice the 
line voltage^ with nothing -to oppose it but the very low 
resistance of the armature winding and connections. This 
would result in a flow df an enormous current — sufficient 
to burn up the arniature in short order — if the safety fuses 
did not melt promptly. 

HYDRAULIC ELEVATORS. 

The mechanism of a hydraulic elevator consists of a 
cylinder and piston, the piston being connected by one 
or more piston rods to a cross-head which carries the 
sheaves over which run the lifting cables from which 
the car is suspended. By means of suitable valves, and con-. 



trolling mechanism operated from the car, water, under 
pressure from compression, or gravity tank systems, or 



Hydraulic Elevators 



945 




Pig. 3S9 



'from street mains where sufficient pressure is available, is 
caused to flow into^ and out .of the cylinder, thus causing 



946 Steam Engineering 

the piston to move from one end of the cylinder to the 
other^ and back again. This motion of the piston and 
cross-head to and fro imparts motion to the lifting cables 
which pass over sheaves at the top of the elevator hatchway, 
and which hold in suspension the car^ thus moving it np 
or down, according as the water flows into or out of the 
water cylinder. 

. The motion of the piston transmitted to the cable is 
multiplied to a greater or less degree, according to the 
design of the elevator, by being caused to pass over sheaves 
designed for that purpose. 

Thus the ratio of increase in speed may be anywhere 
from 2 to 1, to 12 to 1, to meet the requirements due to the 
nature of the service, whether freight or passenger. The 
height of the building also controls in a large measure the 
speed, for instance in very tall buildings the elevators may 
be geared as high as 12 to 1. 

The cylinders of hydraulic elevators are made either ver- 
tical, or horizontal depending upon local conditions. If 
the floor space is restricted, vertical cylinders are used, | 
but in cases where space above the basement floor for the 
accommodation of vertical machines cannot be easily ob- 
tained, it is the usual practice to place horizontal cylin- 
ders in the basement. Vertical cylinders are usually geared 
three and four to one, although ratios of from two to one, 
up to six to one are quite common. 

Fig. 389 presents a view of a low pressure vertical cylin- 
der hydraulic elevator geared two to one. The cut shows 
the general arrangement of the mechanism, from base- 
ment to top sheave. This type of hydraulic elevator is 
operated by the movement of the hand rope n, which passes 
around a sheave at the side of the valve chamber, and 
moves the valve by means of a rack and pinion gear. 



Hydraulic Elevators 947 

Eope n then passes under two small sheaves at the bottom 
of the elevator .hatchway^ and from, thence up to the top 
of the hatchway^ and over another small sheave. One side 
of this hand rope passes through the car^ and by pulling 
this side up the operator causes the car to descend, and by 
pulling the rope down the car will ascend. Near the top, 
and bottom of the hatchway two balls m and m' are placed 
upon the hand rope. , They are large enough to prevent 
their passing through the openings in the floor, and roof 
of the car through which the hand rope passes. When the 
car ascending strikes the upper ball m, the latter is carried 
up with the car, thus pulling up the hand rope, and moving 
the control valve back to the stop position. Should the car 
fail to stop, the valve will be carried past the stop position, 
which will connect both ends of the cylinder, and the car 
will start to descend. If, however, every part is properly 
adjusted, this reversal of the motion of the car cannot 
occur, because under such conditions, the car will stop 
when the valve is closed. If by any mishap the car should 
run away, and go beyond the normal limit of its travel, the 
control valve would be slightly opened in the opposite direc- 
tion, just sufficient to develop a retarding force and thus 
stop the car. The action is thesame when the car approaches 
the bottom, as it will then strike ball m', which will be 
carried down, thereby closing the operating valve. Balls 
m and m' are in fact automatic top and bottom limit stops, 
and constitute one of the most valuable safety devices with 
!i which elevators are equipped. 

Another valuable device is the speed limit, which usually 

■consists of stops mounted at some convenient point in the 

'hatchway, and set above and below balls m and m', so as to 

limit the distance through which the latter can be moved. 



948 



Steam Engineering 



In some cases additional stop balls are nsed^ on account of 
its not being convenient to place stops to act directly upon 
m and m'. The positions of these stops which limit the 
amount of opening of the valve^ are determined experi- 




FiG. 390 



mentally when the elevator is installed. The movement of L, 
the car is kept steady by guides M, M, Pig. 389. In the Lj 
•construction shown in Pig. 389 these guides are made of I \ 
hard wood. At the top of the car adjustible shoes aref 



Hydraulic Elevators 



949 



provided, which slide freely against the guides. At the 
bottom the car is guided by jaws formed in a safety device, 
or "safety^^ as it is termed. It is made of hard wood blocks, 
the dimensions varying from 4 inches thick by 11 inches 
wide in the smaller sizes, to 5 in. x 15 in. in the larger 
sizes. The jaws of this safety are reinforced with massive 
iron castings, and on one side are provided with a wedge 
that can be adjusted in position by means of screws, and on 




Fig. 391 

the opposite side with another wedge that can be forced 
between the guide and the jaw to stop the car if one of the 
lifting ropes breaks, or the car attains an excessive velocity 
from any cause. 

By reference to Fig. 390, and also to Fig. 391, which 
Miows one end of the safety device, its construction and 
ie| Dperation will be clearly understood. 

In Fig. 391 the governor rope rod L is shown only in 
lekhe end elevation. Eeferring to Fig. 390 it will be seen that 



950 ' Steam Engineering 

the two lifting ropes that run down to either side of the 
car are connected with the ends of a rocking lever C. This 
lever C^ as shown in Fig. 391, is pivoted at D'^ hence if 
either one of the lifting ropes breaks, the end of the lever 
it is attached to will drop down. The shaft 11 which 
extends under the car from one side to the other, carries at 
its ends a lever L' which^ when raised lifts the wedge N" 
and forces it into the space between the guide M and the 
side of the jaw of the safety plank. Whichever way the 
lever C may be tilted by the breaking of one of the lifting 
ropes, it will rotate shaft H and lever L' in the proper 
direction to throw up wedges N", thereby locking the car 
against the stationary guides M. 

The levers on shaft H are sufficiently long to strike the 
guides M, when raised high enough, and are sharp at the 
ends so that they will cut into the guides. 

It might be thought that if the wedge N is only raised 
far enough to catch in the space between the guide M and 
the safety-plank jaw it would be forced upward so tightly 
as to stop the car without further assistance. This would 
be the case if the wedge had a sufficiently long taper, but 
if it were so proportioned, it would require an enormously 
strong jaw to resist the bursting strain ; moreover, the car 
would be so tightly wedged that it would require a greater 
force to release it than could be easily obtained. 

With the wedges of the proportions used, it is necessary ^ 
to make the lever that lifts the wedge so that it will dig 
into the guide, and as the car moves down through, say, a 
foot or two in coming to a stop, the lever shaves the side j '^' 
of the guide, thereby not only forcing the wedge tighter k^'' 
against the guide, but producing an additional retarding 
force. When a car is caught by the safety, all that is neces- 



Hydraulic Elevators 



951 



sary to release it is to start in the upward direction, and the 
force exerted by the lifting cylinder is enough to overcome 
the friction of the wedges against the guides. , ,. . 

In the foregoing it is shown how this safely acts, provid- 
ing one of the ropes breaks. Elevator cars, however, seldom 
drop when one of the ropes breaks, but frequently attain 




Fig. 392 

a very high velocity when the ropes do not break, and on 
that account it is necessary to arrange the safety so that 
it will act when the speed reaches a certain stage regard- 
^less of the cause of increased velocity. This is accom- 
plished by means of the Otis safety governor, shown 
^mounted on one of the overhead beams in Pig. 389, and in 
detail in Fig. 392. This device is driven by the rope L, 



yD2 steam Engineering 

which is made fast to one end of lever G' as shown in 
Fig. 389. The spring that holds G' is strong enough to keep 
the lever in its normal position and rotate the safety gov- 
ernor at a velocity proportional to the speed of the car. 
Eef erring to Fig. 392 it will be seen that the governor may 
be adjusted by means of the spring on the spindle^ to act at 
any desired velocity. The governor driving rope passes^ 
through the clamping jaws H H'^ and when the governor 
speed becomes great enough to lift the rod Z and throw 
the jaws together^ the rope will be clamped. Then, as the 
rope cannot move, the outer end of the lever G' on the 
safety plank will be held stationary as the car descends; 
hence, the shaft H will be rotated, throwing the safety 
wedges N into action to stop the car. It is evident that 
the car can descend only as far as the upward movement of 
the end of lever G^ and the compression of the spring on 
L will permit, before the rope will be compelled to slide 
through the clamps H, H' of the governor. As the distance 
through which the spring can be compressed, plus the move- 
ment of the end of G' is only a few inches, it is evident 
that unless the car is stopped very short, the rope L must 
break if it cannot slide through clamps H, H'. The dis- 
tance in which the car will stop is always considerably more 
than the compression of the spring plus the movement of 
the end of G'; hence, while it is necessary for H H' to 
clamp the rope tight enough to move G', the pressure must 
not be so great as to prevent the rope from slipping. For 
the same reason, in order to make the safety governor 
reliable it is necessary that the operating rope shall be in 
just as good condition as the elevator lifting ropes. The 
failure to inspect this rope properly, and make sure that 
it is at all times in perfect condition has been a prolific 

cause of accidents. 

I 



161 



Hydraulic Elevators 



95^ 




Fig. 393 

The jaws of the safety plank and the wedge N should be 
kept clean and in proper adjustment at all times. 



As the 



954 Steam Engineering 

guides M have to be kept well lubricated;, it can be easily 
seen that if the safety jaws are neglected they will soon 
become clogged with a mixture of grease and dust^ and this 
may give a considerable trouble by causing the wedge to 
stick to the side of the guide and thus go into action when 
everything else is running properly. The wedge N, and 
the adjusting wedge on the opposite side of the guide, will 
gradually wear away. For this reason the latter should 
be set up as often as required to keep the proper amount 
of clearance between the guide, and the safety jaw. If the 
clearance is too great, the wedge N is liable to not catch 
firmly when called into action, and if the clearance is too 
small, the safety is liable to act when not required. 

The operating valve shown in Fig. 389 is the same in 
principle as the one shown in section in Fig. 393, but it 
has several details of construction not shown in the latter. 
Its design is shown more in detail in Fig. 394, which is a 
sectional elevation of the valve, and casing. The casing 
is made in three parts marked 7, 8 and 9. Part 7 forms 
the top, and provides a dome, into which the rack 6 on the 
end of the valve rod can rise as the valve is lifted by the 
rotation of the pinion on the end of the shaft A. This 
shaft carries at its outer end the hand rope sheave shown 
at the side of the valve in Fig. 389. The parts 7 and 8 are 
divided at the center of the shaft A, and form a bearing 
for the latter. 

The lower part 9 which is the valve casing proper, has 
ports 10 and 11 for connection with the lower end of the 
circulating pipe, and the lower end of the cylinder, in the 
manner indicated in Fig. 393. That portion into which 
the circulating pipe is connected forms a separate casting 
in Fig. 389, and the casing 9 is bolted to it. Port 12 in 
part 9 of the valve casing is for the purpose of connecting 



Hydraulic Elevators 



955 




Fig. 394 



956 Steam Engineering 

with the pressure-water supply if for any reason it is not 
desired to have this connectiorr made in the circulating 
pipe. The valve casing is lined with brass tubing 4 and 3. 
Lining 4 is simply for the purpose of providing a smooth 
surface for the cup packing of V to slide against. Lining 
3 is provided for the purpose of making ports of such a 
character that the cup packings of V may be able to slide' 
over them freely. 

If the ports were large openings^ the packings could not 
pass over them, because on the up movement they would be 
caught by the edges of the ports. With the brass linings 
this trouble is overcome by perforating the brass with a 
large number of small holes, about one-quarter of an inch 
in diameter. The combined area of the holes is much 
larger than would be required in a single port, this increase 
in opening being provided so as to reduce the friction of 
the water running through the holes by reducing the 
velocity of flow. 

The pressure of the water tends to force the valve piston 
V up, and the other piston V down, and as both pistons 
are the same in diameter, the valve is balanced. Never- 
theless the force required to move the valve is considerable, 
owing to the friction of the cup packings, caused by the 
pressure of the water acting upon the entire surface of the 
leather in contact with the brass linings of the valve casing. 

On this account the pinion on the shaft A, through which 
the valve is moved, is made very small, while the hand rope 
sheave is large — about 20 inches in diameter — so that while 
the valve travels a few inches in either direction the hand 
rope has to be pulled through a distance of from two to 
four feet, according to the size of the valve and the speed of 
car. For high car speeds the hand rope movement is in-jji| 
creased, so that the automatic top and bottom stops may 



Bl 



pip 



! 



Hydraulic Elevators 957 

be able to arrest the movement of the ear without making 
the stop abruptly. Eeference to Fig. 394 will show that 
the lower head that clamps packing 2 is made tapering. 
This is done in order to prevent too quick a closure of the 
outlet from the lower end of the cylinder when the valve is 
moved down to stop the car on the up trip ; otherwise the 
stop would be too abrupt. Even with this precaution it 
is possible for the operator to close the valve too quickly; 
therefore a check valve is inserted in the passage connect- 
ing the valve casing with the cylinder. 

This check is directly under the lower end of the circu- 
lating pipe, so that if the operator closes the valve too sud- 
denly the descent of the piston within the cylinder will not 
be arrested instantly, but the piston will slowly continue 
its movement and gradually force the water under it to 
pass through the relief check valve, into the circulating 
pipe, and thus into the top end of the cylinder. If the 
operator moves the hand rope so quickly on the down trip 
as to produce a violent stop, the piston will continue to rise 
in the cylinder, and the water above it which cannot pass 
to the lower end of the cylinder on account of the valve 
being closed, will be forced back through the inlet pipe I to 
the pressure tank. In this case, as no water can pass into 
the lower end of the cylinder, the continued upward move- 
ment of the piston causes it to leave the water, and thus 
a vacuum is formed underneath it. 

This vacuum together with the tank pressure on top of 
the piston soon arrests the movement of the car, but the 
'stop is not so sudden. One objection to having the 'con- 
Jiection from cylinder to pressure tank through the inlet 
oipe I is, that if for any reason the pressure in the tank 
;hould drop to zero, owing to the starting of a bad leak, 
he water in the top end of the cylinder could immediately 



958 



Steam Engineering 



Valve Bea^] 




Fig. 395 



Hydraulic Elevators 959 

run out with such freedom that if the car should happen 
to be at^ or near the top of the hatchway it would attain a 
dangerous speed by the time it reached the bottom. But 
by locating the pressure tank on the roof of the building 
the danger from this source is obviated^ for the reason that 
the flow of the water from the cylinder would then be 
against a pressure due to the elevation of the tank^ and to 
this may be added the pressure of the atmospkere^ for the 
reason that the valve being closed^ no water can pass into 
the lower end of the cylinder, and as the piston moves up, 
a vacuum is formed under it thus tending to retard its 
motion. 

The result is that the combined pressures are sufficient 
to hold the car within safe speed limits. When the pressure 
tank is located in the basement, the danger above referred 
to is avoided by using a valve of the type shown in Figs. 
395 and 396. Fig. 395 shows the casing, and Fig. 396 the 
valve. 

The difference between this valve and that of Fig. 394 
is that it is provided with an additional piston V", see Fig. 
396, which is called the throttle valve. When this valve 
is used, the inlet pipe from the pressure tank is attached 
to the port 12. When the elevator is stopped, the throttle 
valve V" is directly opposite the port 12, and thus obstructs 
the flow of water from the port 10. It will be seen that a 
groove is turned in V" at the center line. In addition the 
valve is not made a perfect fit in the casing, and the clear- 
ance thus afforded is sufficient to permit water to pass by 
in as large an amount as may be required to prevent a too 
sudden stoppage of the car should the operator close the 
valve too quickly. Another advantage is, that in case the 
tank pressure should fail, the flow of water past this clear- 



960 



Steam Engineering 




Fig. 396 

ance is retarded sufficiently to prevent a dangerous speed 
in the descent of the car. • 



Hydraulic Elevators 



961 



When the valve is moved in either direction to set the 
car in motion^ water passes from port 12 to port 10 through 
side ports 14. A portion of this water passes directly from 
12 to 14^ and the other portion passes around the upper 
lining 4, through circular passages 13^ and thence down 

.1 




Fig. 397 



into 14^ as indicated by the arrows. In this way sufficient 
opening around the throttle valve is afforded even when 
the port of the operating valve piston V is only slightly 
open. The passages 13 and the connection between the 
ports 14 and 10 are not easily made out from Fig. 395, but 



962 Steam, Engineering 

the arrows indicate the course of the water, and these make 
the construction more easily understood. The lower cross 
section through the passages 13, taken at right angles 
to Pig. 395 will serve to illustrate more fully the construc- 
tion. 

The pistons used in vertical hydraulic elevators are made 
in several designs, some being arranged so as to be packed 
from the upper end, and others so as to be packed from the 
lower end. Fig. 397 shows one of the latest designs of pis- 
tons arranged to be packed from the lower end of the cylin- 
der, which appears to be the favorite type now. The draw- 
ing shows a section through the complete piston, with pack- 
ing in place, also a section of the cylinder C. 

Ordinary square packing is used, and this is held in. 
position by a follower secured by six bolts. Fig. 398 shows 
the body of the piston only. The parts P and P" are made 
to fit the cylinder, but the intervening section is cut away 
on opposite sides, so as to afford space for the ends of the 
piston-rods and their fastening nuts. The top and bottom 
parts of the piston are connected by the pillars I and I. 

In packing these pistons it is necessary to be careful not 
to press the packing in too tight, as there is danger of burst- 
ing the cylinder by so doing, and even if this much damage 
is not done, the friction caused by the excessive pressure 
may be so great as to prevent the car from attaining its 
full velocity. If a hard packing is used, and this is forced 
into place dry and very tight, the chances are that when it 
becomes well soaked it will expand enough to burst the j 
cylinder. Bursting hydraulic-elevator cylinders is not a ' 
very rare occurrence, and when it does occur it is due to 
too great pressure of the piston packing against the sides 
of the cylinder. 



Hydraulic Elevators 



963 



y-Lj— 






ijj'-n 




1 






1 

5-!- 




v_____ _, 


1 
1 

1 




^ 1 

k. y 






1 

1 


1 P' 


















I 






t 




^ 






J 










P 






„ Pi 1 


A. 


» i 






" ' u. 






->i 






Fig. 398 



964 Steam Engineering 

Eeferring to Fig. 389, it will be noticed that there are 
two piston rods, E. 

This construction was adopted in the early days of hy- 
draulic elevators partially to increase the safety of the 
apparatus, but principally to prevent the traveling sheave 
B from twisting around. The ropes tend to hold the sheave 
from twisting, but they will not prevent slight movements, 
while the double piston-rods will. Now and for several 
years past, however, the frame of the traveling sheave has 
been made in the form of a crosshead running in stationary 
guides, thus effectually preventing any side movement of 
the sheave. With this construction the main benefit of the 
double piston-rods is additional safety; while it is possible 
for one rod to break or become loose, it is practically im- 
possible for both to give way at the same time. 

The arrangement of the cylinder C, the circulating pipe 
K, and the valve V, in Fig. 389, is the same as in the dia- 
gram Fig. 393, even the inleit I being similarly situated. 
The small pipe c is for the purpose of carrying off the drip 
from the upper side of the top cylinder head, ordinarily, 
and also for the purpose of draining the water from the 
upper end of the cylinder, in cases where it is necessary to 
run the piston to the top of the cylinder to renew or adjust 
the packing. Some cylinders are arranged to be packed 
from the upper end and others from the lower end, the 
latter design being the one generally used in modern ma- 
chines. As will be noticed, the pipe c connects at the bot- 
tom of the cylinder with other pipes that connect to the 
valve chest and the lower end of the cylinder. All these 
pipes are either to carry off the drip or to draw water from 
the various parts of the cylinder and valve chest when 
desired. Globe valves are placed in the drainage pipes so 
as to keep them closed normally. 



Hydraulic Elevators 965 

Counterbalance. — Generally a portion of the counter- 
balance is placed on top of the piston^ so that in such ma- 
chines the counterbalance weight is divided into three parts, 
one being within the cylinder^ one in the traveling sheave 
frame^ and one constituting the independent counter- 
balance. 

Operating Devices. — In order if possible to avoid the 
uncertainty of operation in connection with the hand rope 
in high speed elevators^ lever^ and wheel operating devices 
have been developed^ and to make these devices operative 
and reliable^ the operating valves have been somewhat modi- 
fied in design. The main valve^, controlling the flow of water 
into^ and "out of the cylinder^ varies in diameter from 3 
inches in small machines^ to 7 or more inches in the large 
sizes. Fig. 399 shows the lever device for operating^ a 
modern high speed hydraulic elevator. The lever L is 
shown located in the car. The movement of this lever to 
one side or the other rocks the horizontal lever M, and this 
motion causes the sheave P mounted on the frame I to 
rotate through a small angle. The rotation of P is trans- 
mitted to P' through the rope k, and the rotation of.P' 
actuates the valves in a manner that will be presently ex- 
plained. 

Eopes m m^ n n pass around sheaves IST N N K located at 
top and bottom of the elevator hatchway^ as is clearly 
shown. The ends m m are fastened to the ends of the 
lever M but the sides n n are not connected with it^ although 
in the illustration they look as if they were. The side n 
that runs up from the right-hand side N sheave at the bot- 
tom passes over the N sheave at the left-hand side at the 
top of the elevator hatchway. These two N sheaves at the 
top are mounted upon a frame I which is arranged so as 
to hold the sheaves firmly in the horizontal position^ but 



966 



Steam Engineering 





Fig. 399 



Hydraulic Elevators 967 

allows them to revolve freely around the studs upon which 
they are mounted. The frame I is suspended from a rope 
that passes over the two small sheaves resting on top of the 
overhead beams. The end of this rope extends downward^, 
outside of the elevator hatchway^ and has a weight sus- 
pended from it so as to hold the ropes m m, n n^ with the 
proper tension. 

Upon the larger sheave P are mounted the lower N N" 
sheaves. If the right-hand end of lever M is depressed, 
the right-hand loop formed by the rope n m will be low- 
ered^ while the left side end will be raised, and as a conse- 
quence the right side lower N sheave will swing downward 
while the left side one will swing upward. Thus the rope 
k will be pulled with the upper side moving from left to 
right, and sheave P' will be rotated in the direction in 
which the hands of a clock move. 

This arrangement of ropes for transmitting the motion 
of lever L to sheave P' is called the running rope system. 
There is another way of accomplishing the result with sta- 
tionary ropes, the upper ends of these being attached to 
the upper frame I and the lower ends to the sides of sheave 
P, or to the ends of a lever secured to this sheave. In this 
arrangement the rope that is fastened to the right-hand 
side of sheave P is secured to the left side of the upper 
frame I. The sheaves N IST N IST are placed upon the ends 
of lever M and each rope passes over one sheave a;t one end, 
and under another sheave at the other end of M. This is 
the standing rope system. Por both systems there are sev- 
eral modifications, but the results are the same in each 
case, viz., to transmit the motion of lever L to sheave P'. 

Valve V controls the flow of water into and out of the 
ydraulic cylinder. This valve is actuated by a piston T 
j^cated in the enlarged portion of the valve chamber, and 



I 



968 Steam Engineering 

which is larger in diameter than valve v ; consequently if 
water under pressure is admitted to the space between T 
and v^ the pressure of the water upon the larger area of 
piston T will cause it to move up, provided there is no 
pressure on its top side. If water under pressure is ad- 
mitted to both sides of piston T, it will be balanced and will 
exert no force to move the valve in either direction. Valve v 
will, however, have the pressure acting upon its upper side, 
while the only pressure acting against its lower side will be 
atmospheric pressure, or that of the tank into which the 
water is discharged. Consequently the valve will move 
downward. Water is admitted to the space above piston 
T through a small pilot valve at h which is connected with 
the pressure pipe through pipe g, while pipe f connects it 
with the space above T. 

When the car is at rest, pilot valve h is in a position to 
close the ports connected with pipes g and f, and also pre- 
vents the escape of water into the larger pipe connecting 
the lower end of the pilot valve chamber with the main 
discharge pipe. Under these conditions, the water in the 
main valve chamber above piston T cannot escape unless 
valve h leaks. When sheave P' is rotated in a clockwise 
direction, the crank on the end of the shaft will draw down 
the connecting rod j, and as valve h can move much easier 
than main valve v and piston T the latter will remain 
stationary,, while h will be depressed. This movement of 
h will uncover the ports connecting with pipes g and f, thus 
establishing a through connection between the pressure pipe 
and the space above T and the latter will be forced down- 
ward, carrying with it throttle valve V which will uncover 
the port connecting with pipe G, and also move the main 
valve V far enough down to uncover the upper edge of the 
port connecting with the lower end of the cylinder, thus 



Hydraulic Elevators 969 

opening a communication between the two ends of the 
main cjdinder. Under these conditions the weight of the 
elevator car which acts to pull piston P upward will set 
the latter in motion, and the water in the upper end of the 
cylinder E will be forced down through pipe G and 
through the valve chamber, around valve V into the lower 
end of the cylinder. The pipe G is called a circulating 
pipe, as one of its objects is to provide a path through 
which the water may circulate between the top and the 
bottom of the cylinder E. 

As the action just explained takes place when the ele- 
vator car descends, it will be seen that, for the down trip, 
no water is drawn from the pressure tank. To run the 
car upward, the sheave P^ is rotated counter clockwise by 
-swinging the car lever L in the opposite direction. When 
P^ is so rotated, the crank on the end of the shaft will push 
connecting rod j upward, and thus pull on rod i and 
thereby lift the pilot valve h. The upward movement of 
h uncovers the port that connects with pipe f, but keeps 
that connecting with pipe g closed, so that the water con- 
fined in the valve chamber above T can now escape through 
pipe f, and the lower end of the pilot valve chamber into 
the discharge pipe. In this way the pressure acting on 
the top side of T is removed, and the pressure acting 
on the bottom side forces the valves up, owing, as has been 
already explained, to the difference in area between T and 
valve V. The upward movement of valve v opens communi- 
cation between the port running to the lower end of the 
hydraulic cylinder, and the discharge pipe, thus permitting 
"the water in the lower end of the cylinder to escape through 
*the discharge pipe. This upward movement of the valves 
ialso raises throttle valve V and allows the water in the 
^pressure pipe free access to the port connecting with pipe 



970 Steam Engineering 

G, thus admitting a new supply of water under pressure 
to the space above the piston in the hydraulic cylinder. 
Under these conditions the water acting upon the top side 
of piston P in conjunction with the vacuum formed under 
the piston by the escape of the water into the discharge 
pipe^ provides the force that depresses the piston and 
thereby lifts the car. 

TJpon the rate of flow with which the water can enter, 
or pass out of the cylinder will depend the velocity with 
which the piston will move^ and this rate of flow is evidently 
dependent upon the extent to which the valves are opened. 
If the operator in the car desires to run at a slow speed, 
he moves lever L a short distance from the .central posi- 
tion; for a higher speedy he moves it further from the 
center^ and for the highest velocity, he moves it as far 
as it will go. 

Now suppose L is moved a short distance only, then 
sheave P will be rotated through a short angle, imparting 
a correspondingly small movement to connecting rod j. 
Suppose j is depressed, thus opening the connection be^ 
tween pipes g and f — water will begin to flow into the 
space above T as soon as pilot valve h moves down far 
enough to uncover the ports connecting with pipes g an (J 
f and draw down the end S of lever Q. As j will now 
be stationary, it will act as a fulcrum, and E will 
lifted. This movement will continue until pilot valve 1 
is raised sufficiently to cover the ports connecting witr 
pipes g and f, which will stop the flow of water into the 
space above T. It will thus be seen that, after pilot valv- 
h has been moved by the rotation of the sheave P', maiii 
valve V, and piston T also begin to move, and as the; 
move, the pilot valve is returned to stop position. If pilo 
valve h is moved but a short distance from stop position 



to 



fte 



Hydraulic Elevators 971 

piston T and valve v will have a correspondingly short 
distance to move to return the pilot valve to stop position. 
' The amount of opening given to pilot valve h depends upon 
the distance the car lever L is moved. If for a short dis- 
tance^ the opening will be but a small fraction of its travel, 
and the main valve will open a correspondingly short dis- 
tance^ and vice versa. As water is practically incompres- 
, sible^ it is apparent that if lever L be too quickly moved 
^ to the central position when the car is moving at a high 
\ rate of speedy the motion will be arrested with a violent 
jerk. In order to prevent such action^ means are provided 
; whereby the water may find an outlet, if the valve is closed 
too suddenly. If the sudden stop occurs on the downward 
trip of the car, which is the up-strokp of piston F, the 
'Water will leak by the throttle valve Y and flow back into 
I the pressure pipe, and will continue to flow until the car 
:has come to a stop. 

If the throttle valve V were not provided, the water 

^; would escape too freely, back into the pressure pipe, and 

as a result the car could not be stopped in a very short 

'distance; hence, the object of valve V is to provide means 

'to prevent a too sudden stop of the car on the down trip, 

and at the same time not to permit the car to run farther 

'than is necessary to make a gradual stop. Valve V is 

not water-tight, as has already been explained (see Fig. 

396), and its throttling action begins gradually. 

Should the car be stopped too suddenly on the up-trip, 

the water in the lower end of cylinder E will be forced 

I through valve d at the bottom of pipe G, and the mo- 

imentum of the nioving parts will be expended in com- 

Lpressing the spring that holds valve d to its seat. Fig. 399 

has been reduced in length, but it shows in detail all of 

the mechanism of a modern type vertical cylinder hy- 



972 



Steam Engineering 




Fig. 400 



Hydraulic Elevators 973 

draulic elevator^ with running rope or standing rope con- 
trol. Other methods of control besides those already de- 
scribed are in use^ mainly in private dwellings and other 
places where an .operator is not employed. These consist 
of magnetic controllers for operating the pilot valve by 
means of push buttons, the magnets being operated by 
current from the incandescent light circuit, or if such a 
circuit is not available, the current is derived from pri- 
mary, or storage batteries. 

Horizontal Cylinder. — The principal difference between 
the vertical, and the horizontal cylinder types of hydraulic 
elevators lies in the fact that in the one type the cylinder 
stands in a vertical position, while in the other it is placed 
horizontally. The principles governing the operation of the 
valve mechanism are practically the same in both cases, 
outside of a few details which will be explained. Fig. 400 
shows the general arrangement of a horizontal cylinder 
hydraulic elevator, including pump and pressure tank. 
The type here illustrated and described is the Crane push- 
ing type elevator, there being two distinct classes of hori- 
«ntal hydraulic elevators, viz., the pushing and pulling 
pes. Eeferring to Fig. 400, the stationary sheaves and 
Tear end of the cylinder will be, seen close to the hatch- 
way. The main valve which controls the admission and 
release of the water to and from the cylinder is located 
K, and is automatically operated by the movement of 
1 pilot valve L, the latter being actuated by the rocking 
shaft M, which is done by means of rods m m con- 
ted with a running rope system operated by the lever 
the car. An automatic stop valve is located at E simi- 
^■^lar in design to that described in connection with vertical 
cylinder machines. This valve is actuated by the median- 



974 



Steam Engineering 



ism at N^ which is set in motion by the movement of the 
crosshead. 

Figs. 401^ 402 and 403 show the apparatus in detail. 




Fig. 401 



In Pig. 401, which is a side elevation, it will be seen that 
if lever S is moved in either direction, the rods m m will 




Fig. 402 



cause shaft M to rock, thus moving the pilot valve by ,|| 
means of valve rod L'. Moving the pilot valve will either 1^ 




Fig. 403 

open or close main valve K, which will allow the water to 
flow into, or out of the cylinder, depending upon what 
direction lever S is moved. 



Hydraulic Elevators 975 

If the operator fails to return lever S to stop position 
when the car reaches* the top of the hatchway, the frame 
N will be carried to the right by the motion of the cross - 
head, and the projecting arm D^, Fig. 402, will strike 
the stop mounted on rod D" connected to the end of the 
frame. This movement of N will cause a roller at n' to 
strike lever o', which will move to the right, and pull 
rod Q with it, and this action will close stop- valve E, 
which will stop the flow of water into the cylinder, and 
the car will come to a stop. 

Should the car be descending, the main piston will be 
moving to the left, and if lever S is not returned to stop 
position at the proper time, the automatic stop will act in 
precisely the same way, except that frame N will be moved 
to the left instead of to the right. 

Eeferring to Pig. 403, which is a sectional elevation of 
the cylinder, piston, sheaves and connecting parts, it will 
be seen that there is a rubber ring around the piston end 
of the plunger E, and a similar ring in the crosshead D. 
A strong buffer frame I is attached to front cylinder head 
G. The function of these parts is to act as cushions in 

^ case the car travels past its normal position at either end. 

^ These parts should be adjusted so as to prevent the car, or 
counterbalance weight from striking the overhead beams 
in case the automatic stop valve fails to act. 

Pulling Type, — Fig. 404 shows a view of a pulling type 
of horizontal cylinder hydraulic elevator. This machine is 
made by the Whittier Machine Company, and its action 
is as follows : G is the main operating valve, and the pilot 
valve is located directly above it at J. The automatic stop 
valve is at H, and is actuated by stop balls IST mounted on 
rope L. These stop balls are moved by coming in contact 
with an arm attached to the crosshead, which also carries 



976 



Steam Engineering 




Fig. 404 
the whittier pulling machine 



Hydraulic Elevators 



^11 



the traveling sheaves D^ and shoes E on the crosshead 
slide within the side guides. 

The weight P suspended from the chain that travels 
between two small guide sheaves located just below the 
valve casings is for the purpose of bringing the automatic 




■ Fig. 405 

^top valve to central position as soon as the piston moves 
away from either end of the cylinder. The shackle bolts 
for the ropes are shown at Q. 

The main and the pilot valves of the Whittier machine 
are shown in detail in Figs. 405 and 406^ the first being a 



< B 




From Cylinder 



Fig. 406 
plan view and the second a sectional side elevation. Ee- 
f erring to Fig. 405^ it will be seen that the operating lever 
K is pivoted at the point F^ so that when actuated by the 
operating ropes AA' it imparts an end movement to the 
pilot valve rod C. The ropes A A' are connected with the 



978 



Steam Engineering 



operating lever in the car by either a running, or a stand- 
ing-rope arangement identical with those used for vertical- 
cylinder elevators. 

In Fig. 406 the pilot valve rod C is shown connected 
with the top end of lever D, the latter being pivoted at G. 
The part B, which holds the pivot G is actuated by the 
lever K. The supply pipe is connected with the right-hand 
end of the pilot-valve chamber through the pipe E. If the 
rod C is moved to the left, high-pressure water will pass 
through the pilot valve to the end I of the main valve and 
force the latter to the left, thereby connecting the cylinder 
with the discharge pipe, when the water will run out and 
the elevator car descend. The forward movement of the 




Fig. 407 



main valve will carry the lower end of the lever D to the 
left and the upper end to the right, until the pilot valve 
is returned to the closed position. If the pilot-valve rod 
C is moved to the right, the end I of the main valve 
will be connected with the discharge and the water will 
escape, then the pressure acting on the piston L will force 
the valves to the right and connect the supply pipe with 
the cylinder, which will fill with water from the pressure 
tank and the car will be forced upward. The movement 
of the main valve to the right will carry the lower end of 
the lever D in the same direction and the upper end to 
the left, and return the pilot valve to the central position. 



Hydraulic Elevators 979 

The pilot valve shown in Fig. 406 is provided with 
stuffing-boxes at each end to insure tight joints with the 
valve-rod;, but this construction is not used in all the 
Whittier elevators; in some of them the pilot valve is 
made as shown in Fig. 407^ where the escape of water at 
the ends is prevented by the use of cup packings. The 
pressure water enters through the port A^ the discharge 
being through the port B; consequently^ the cups are set 
so as to oppose the pressure which is exerted in both di- 
rections from the port A. 

Another design of the pulling-type elevator is presented 
in Figs. 408, 409 and 410. This is called a ''double-decked'' 
machine, and is made by Morse^ Williams & Co., of Phila- 
delphia. Why it is called double-decked can be understood 
from Fig. 408, which is a side elevation and shows two ma- 
chines placed one over the other. In buildings where floor 
space is limited, this construction is often adopted, in some 
cases three and four machines being installed one over an- 
other. Fig. 409 is a top view of Fig. 408, and Fig. 410 
is an end view seen from the right side. In these machines 
there is but one piston rod, as at B., Fig. 408. The 
crosshead is similar to that in the Whittier machine, except 
that the sides of the end bars are square with the side 
frames, instead of in line with the traveling-sheave shaft, 
as at J, Fig. 410. The guides F are set so that the 
crosshead shoes a, slide on top of the upper flange, not 
between the flanges. 

At the stationary-sheave end of the guides there are 
shorter guides U, which carry a shaft provided with small 
rollers b, the function of which is to support the ropes 
running over the upper sides of the sheaves. In Fig. 408 
the upper machine is shown with the traveling sheaves 
close to the stationary sheaves, caused by the car being at 



980 



Steam Engineering 




r^^ 



the lower floor of the building. In this machine the sup- 
porting rollers b' are at- the extreme right-hand end of 



Hydraulic Elevators 



981 



the guides U'. In the lower jnachine sheaves D are close 
to the cylinder^ as they will be when the elevator car is 
at the top floor. In this case the supporting rollers b are 
at the extreme left-hand end of guides U and midway be- 




FiG. 410 



tween the sheaves D and E^ the better to support the ropes 
at the central point. On the upper machine in Fig. 408* 
a hook 1 mounted on a shaft carried by the guide shoes c' 
engages a -piece e^, secured to the part J', as shown in Fig. 
510, at the center. At one end of the shaft which carries 



982 ♦ Steam Engineering 

hook 1 there is a lever k. When the sheaves D' move to- 
ward the cylinder, the hook 1 being engaged with lever e, 
the supporting rollers b' are carried along with the hook ] 
until lever k reaches an inclined plane m, up which the 
rollers slide, causing the shaft to be rotated and hook 1 
to be pulled up' out of the way of the lever e, the rollers 
being left in the position of those shown on the lower 
machine. The supporting roller shaft is kept in line, 
notwithstanding that it is carried along by the part e 
acting at the central point, by reason of the guide-shoes c 
being provided with grooves that fit over the guides U, as 
clearly shown in Fig. .410. When the traveling sheaves 
move forward, the piece e engages hook 1 when the latter 
is reached, and the roller shaft is carried forward to the 
end of the guides, as shown at b. These supporting rollers 
relieve the ropes of considerable strain when the stroke is 
long, and the traveling sheaves are near the cylinder, but 
they are of little service in short-stroke machines. The 
movement of the roller shaft is equal to one-half the stroke 
of the machine. 

The Stop and Main Valves. — In a machine of the pull- 
ing type the piston is forced toward the back end of the 
cylinder on the upward motion of the car. If the auto- 
matic stop-valve is properly adjusted, it will begin to close 
at the right time to stop the car even with the upper floor ; 
but if it is improperly adjusted, the car is likely to run 
into the overhead beams, therefore buffers g g, faced with 
rubber cushions h h, are provided. In the machine illus- 
trated in Fig. 408 the automatic stop-valve does not fit 
perfectly, and if the main valve is not closed when the 
car reaches the upper floor, the car will not stop but will 
slowly move upward until the crosshead brings up against 
the buffer cushions h h.. On the downward trip, if the 



Hydraulic Elevators ' 983 

main valve is not closed when the car reaches the lower 
floor^, the car will settle gradually until it rests on the 
bumpers^ or the piston strikes the front cylinder head. 

In Fig. 408 the main valve is located at G and is 
actuated by a pinion at n which meshes with a rack in 
the neck-bearing n'. The automatic stop-valve is con- 
tained within the casing H and is actuated by a rod con- 
necting with a crank-pin on a crank-disk mounted on the 
shaft with the sprocket-wheel Q, Figs. 408 and 409. Tne 
sprocket-wheel Q is rotated by means of a sprocket 
mounted on the shaft with sprocket i, Fig. 409^ which 
latter is operated by a chain^ the ends of which are affixed 
to the ends of two square rods^ the lower of which is shown 
at L. Another chain around the sprocket P is connected 
with the opposite ends of these two rods. To stop the 
movement of the piston^ the stop-valve is actuated to the 
left. If the traveling sheave is moving toward the cylin- 
der the actuating bar E attached to the crosshead will 
strike the stop IST and move it to the lef t^ which will set up 
a counter-clockwise rotation of the sheaves and Q^ and 
this" will move the crank-pin and the stop-valve to the 
left. If the traveling sheave is moving away from the cylin- 
der^ the lower end of bar E will strike the stop N on the 
square rod L and^ by carrying the latter to the right, ro- 
tate sheaves and Q counter-clockwise in the same direc- 
tion. The stops N are hook-shaped; they slide over the 
side projections on bar E^ Fig. 410^ and lock with it, 
with the result that when the elevator is started on the 
return trip the movement of the crosshead carries the stop 
N with it, and the automatic stop-valve H is pulled open. 
When the elevator is started it moves very slowly for a few 
inches, as only the water that leaks by the automatic stop- 
' valve is available to move it^ but as the movement of the 



984 



Steam Engineering 




Fig. 411 



Hydraulic Elevators 985 

crosshead also operates the valve^ the opening of the latter 
is rapidly increased and the car speed correspondingly ac- 
celerated. 

"WTien the bar E has carried the stop N as far as the 
stop T the releasing lever S strikes the latter and the hook 
on the stop K is raised so that the bai* E may slide by and 
leave the stop N adjoining the stop T^ ready to be struck 
by the bar E on the next stroke. The actuating stops T 
are not held on the rod L but on a rod directly in front 
of it (see Pig.. 410), and this rod is secured, so it will 
not move endwise, in the frame V. 

Fig. 411 shows a double-deck arrangement of two sepa- 
rate machines. This grouping of horizontal elevator en- 
gines is often resorted to for the purpose of economizing 
space, the machinery for operating two cars occupying the 
same floor area as that ordinarily required for one. 

High Pressure Elevators, — The types of elevators hither- 
to discussed belong in the low pressure class, the water 
pressures used in operating them not exceeding 200 lbs. per 
square inch, the average being about 150 lbs. But the 
increase in the height of modern office buildings, and the 
demand for a high car speed have resulted in the develop- 
ment of high pressure elevators, operating under pressures 
as high as 700 lbs. per square inch, and even higher in 
some cases. 

The reduction in the size of the machine and piping 
that can be effected by using this pressure is much greater 
than would be supposed by those who have not investigated 
the subject. To give a general idea of how great the re- 
duction actually is, suppose a low-pressure elevator has 
a cylinder 16 inches in diameter and works with a pres- 
sure of 100 pounds. For such a machine the supply pipe 
would probably be not less than 6 inches in diameter. Sub- 



986 Steam Engineering 

stitute for this a high-pressure machine working with 800 
pounds pressure per square inch ; then^ if everything else 
remains unchanged^ the area of the cylinder will be re- 
duced to one-eighth, and this will make the diameter a 
trifle under 5% inches, as compared with the low-pressure 
cylinder of 16 inches diameter. This is not all the gain 
that can be made; there can also be effected a great re- 
duction in the size of the supply pipe, for as only one- 
eighth of the quantity of water is required, the size of the 
pipe can be reduced to the same degree as that of the cylin- 
der, provided the water is to run through it at the same 
velocity. This reduction would cut the pipe down from 
6 inches to a trifle over 2 inches in diameter. 

These reductions are not exactly what would be made in 
actual practice, because the frictional loss in the small 
high-pressure cylinder would not be as great as in the 
large low-pressure cylinder, and the velocity of the water 
through the supply pipe could be made greater for the 
same percentage of loss; this would permit a farther re- 
duction in the size of the pipe. In practice the gain in 
this direction is utilized in part to reduce the size of the 
apparatus, and in part to reduce the loss of energy in forc- 
ing the water through the pipes. As a result, the loss of 
energy due to the friction of the water passing through 
the pipes, lifting cylinder and valves is reduced to about 
5 or 6 per cent, whereas in low-pressure machines it runs 
from, say, 10 to 30 per cent. The change of pressure 
from 100 to 700 or 800 pounds brings about other changes 
in the construction of the machine and apparatus and also 
in the general arrangement of the system. 

The arrangement of the various parts of a high-pressure 
system is indicated by the diagram, Fig. 412. This dia- 
gram shows a machine geared six to one. The cylinder is 



Hydraulic Elevators 



987 



shown at C^ the plunger at P and the traveling sheaves 
below it ; the cylinder is inverted^ the plunger being forced 
downward by the pressure of the water. This construc- 




ISuapiog 



Pump to return Pilot Valr* IHsohatst 



Fig. 412 



tion is \ised because the small size of the cylinder makes 
it impracticable to use a piston and piston-rod, therefore 
a, solid plunger is provided and the pressure acts to push 
it out of the cylinder. 



988 Steam Engineering 

In Fig. 412 the pump forces water into the lower end 
of the accumulator, from which a pipe runs to the main 
valve, through which it passes to the pipe A and thence 
to the lifting cylinder. On the return stroke the water 
passes out of the cylinder through the pipe A and through 
the upper end of the main valve to the discharge pipe, 
which runs up to a tank placed on or near the roof of the 
building. The object of this arrangement is to provide 
a low pressure to operate the pilot valve, which is shown 
in the diagram just above the main valve. In the first 
high-pressure elevators made, the pilot valve was operated 
with water at the same pressure that was used for the lift- 
ing cylinder, but these valves were not successful, owing to 
the fact that they had to be very small and the packings 
would not withstand the wear due to the pinhead jets of 
water striking them at terrific velocities; in addition, the 
small holes through which the water passed were soon en- 
larged so that the valve would not work satisfactorily. 
With the low-pressure pilot valve there is no trouble. A 
small tank is provided to receive the discharge from the 
pilot valve and its actuating cylinder, and this water is 
returned to the roof tank by means of a small pump as 
shown in Fig. 412. 

The Accumulator,— The accumulator takes the place of j 
the pressure tank of the low-pressure system. A pressure 
tank cannot be used with the high-pressure system, owing 
to the fact that it is troublesome and expensive to pump air 
against a high pressure, and it is necessary to do this so 
as to replenish the air that gradually leaks out of the pres- 
sure tank. Even if there were no difficulty in pumping air 
into a high-pressure tank, the accumulator would be pref- 
erable, because with it the pressure depends upon the 
weight on top of the plunger, not on the height of the 



Hydraulic Elevators 989 

water in the cylinder. With a pressure tank the pressure 
^^ drops as soon as water is drawn out, and it runs up as 
soon as the outflow stops, consequently the pressure is con- 
tinually varying. 




Fig. 413 



\ The arrangement of the entire apparatus of an Otis high- 
pressure vertical elevator is shown in Pig. 413. This il- 
^lustration shows several parts not represented in the ele- 
^Wntary diagram, Fig. 412. The main pump is at A and 



990 Steam Engineering 

at B is shown the prime mover, which in this case is an 
electric motor, although in practice steam power is almost 
always used. The accumulator is shown at C and the 
main valve, and pilot valve are at D. From the main 
valve the water passes to the lifting cylinder through pipe 
E, passing first through an automatic stop-valve F, thence 
through pipe G to cylinder H. The plunger is shown at 
I, and the traveling sheaves at J. 

The high-pressure water from the accumulator reaches 
the main valve through pipe K and is discharged from the 
valve through pipe L which runs up to the tank at the 
top of the building. Through pipe M, the water returns 
to the pump A. An air chamber is provided at Q to 
smooth out any pulsations of the pump that its own air 
chamber does not subdue. The small pump to return the 
water discharged from the pilot valve to the roof tank is 
also shown. 

It will be noticed in Fig. 413 that the machine proper 
of a vertical high-pressure elevator is not very elaborate. 
• Fig. 414 shows a sectional, and also a plan view of the 
main and pilot valves. 

The pilot valve is at A, and the main valve at C; B is 
a motor cylinder, the piston of which moyes the main 
valve. In this construction, the pilot valve" is not much 
smaller in diameter than the main valve, tod the motoi 
piston is very much larger than the main valve. The dif- 
ference in the proportions of these parts as compared witl 
the valves described in connection with low-pressure ma 
chines is due to the fact that in the high-pressure systen 
the motor piston is actuated by low-pressure water, so a 
to make it possible to use a pilot valve of large enoug] 
size to be durable. As is shown in Fig. 413, the tank int 
which the lifting cylinder discharges is placed high enoug 



Hydraulic Elevators 



991 



to give enough pressure to operate the motor piston^ and 
from this tank water passes through the pilot valve A to 
the cylinder B. If the motor piston were operated by 
the high-pressure water, the pilot valve and its port holes 
would have to be so small that the parts could not be made 
sufficiently substantial. For this reason water at a pres- 




FiG. 414 



sure of about 80 pounds per square inch is used to operate 
the motor piston. 

It might be thought that having to discharge the water 
in the lifting cylinder against a back pressure of 80 pounds 
would cause considerable loss, and make the high-pressure 
system objectionable on the score of low efficiency, but this 
is not the case because the main pump draws water from 



992 Steam Engineering 

this same discharge tank; therefore, the back pressure 
against the lifting cylinder acts to help the pump, so that 
in reality all the work the pump has to do is to force water 
against a pressure equal to the difference between the pres- 
sure of the accumulator and that of the discharge tank. 
The net result is that if the accumulator pressure is 750 
pounds, and that of the discharge tank is 80 pounds, the 
actual pressure against which the pump acts is 750 — 80 
1=670 pounds, and the pressure that acts in the lifting 
cylinder to raise the elevator car is 670 pounds, not taking 
into account the losses due to friction of the water through 
the pipes and valves on its way from the accumulator to 
the cylinder. 

Operation of Main and Pilot Valves. — The operation 
of the main and pilot valve in Fig. 414 is as follows : If 
the operator desires to run the car upward he moves the 
car lever so as to pull up the rope W on the right side, 
thus tilting the rock lever N in a counter-clockwise direc- 
tion. . The levers N and L are secured to the shaft P; 
hence, the end of L will move down and through the con- 
necting rod L' will pull down the lever L" : and the latter, 
through M, will depress the pilot valve. The center pipe 
E is connected with the upper discharge tank : hence, water 
will flow in and through the lower end of the pilot- valve 
chamber, pass to the lower end of the motor-piston cylin- 
der B, and raise the piston, the water above the latter pass- 
ing out into the pilot-valve chamber above the valve, and 
thence to the pipe D. As the motor-piston rod is connected 
at both ends by arms J J with the ends of the main valve 
C, the upward movement of the piston will lift the main 
valve, and then the water from the accumulator coming 
through the pipe I will pass into the center of the main 
valve through the port S. The port Q will be above the 



Hydraulic Elevators 993 

packing R^, so that the water will pass out into the cen- 
tral pipe H and thence to the lifting cylinder^ and by 
pushing the plunger out of the latter will lift the elevator 
car. If the rock lever N is tilted in the opposite direction^ 
the pilot valve will be raised^ and then water will pass to 
the upper end of the motor cylinder and depress the pis- 
ton, thus moving the main valve down so that the water 
in the lifting cylinder may escape through the ports Q' 
into the upper end of the main valve and thence through 
the ports S' to the upper discharge pipe G; from there it 
passes to the discharge tank near the top of the building. 

Cylinder and Plunger, — Pigs. 415 and 416 show the 
construction of the plunger, cylinder, and sheaves of the 
Otis high pressure vertical cylinder elevator. 

Pig. 415 gives external and sectional views of the cylin- 
der, the upper end of which is seen at A and the lower 
end at B. To shorten up the drawing the cylinder is 
broken at C C. The plunger is indicated by D. Above 
the cylinder are shown the stationary sheaves held between 
side f]'ames made of channel iron G, to the lower end of 
which the cylinder is bolted, as shown at G'. The channel 
frames G are bolted to a rod H at the upper end, and 
this is held between beams I that are secured to the wall 
or floor framing of the building. The traveling sheaves 
are carried in a crosshead attached to the lower end P of 
the plunger. 

The internal construction of the cylinder is shown in 
the vertical section, which is taken at right angles to the 
exterior view. The upper end of this drawing shows the 
iway in which the bearings of the stationary sheaves are 
iheld between the side. frame channel beams G G, and in 
Hike manner the lower end shows the construction of the 
cap P that forms the end of the plunger and the support 



994 



Steam Engineering 




Fia. 415 




Fig. 416 



for the traveling-sheave frame. This cap is constructec 
cup-shaped on its upper side to receive the drip from th 



Hydraulic Elevators 995 

cylinder. The plunger^ it will be noticed, does not fit the 
cylinder throughout its entire lengthy but only for a short 
distance at the lower end^ where the stuffing-box is lo- 
cated. The cylinder is held up by the rod H^ and is sus- 
tained against side displacement by means of one or more 
rings K and the frame J^ the construction of both of which 
can be readily understood from the drawings. 

The outlet M in Pig. 415 is the pipe connection through 
which the actuating water enters and passes out of the 
cylinder. T-bars I' V to which the frame J is bolted 
form the guides for the crosshead of the traveling sheaves^ 
and the cylinder is held true with these by means of the 
frame J so as to keep the plunger and the crosshead guides 
in line. 

Pig. 416 shows side^ and edge views of the crosshead, 
the guides, and the traveling sheaves. 

Pig. 417 shows the speed regulator used in connection 
with the Otis high pressure type of elevator. This device 
will not allow the car to attain an excessively high speed 
under any conditions, for the reason that it depends for 
its action upon the velocity of the current of water passing 
through it, and not upon the pressure. The device is con- 
nected in the piping so that the water that flows into or 
out of the lifting cylinder passes through it. If, when 
the car is ascending, the water enters through .port, C, and 
passes out through D, then on the descending trip the 
water will enter through D and pass out through C. In, 
either case, the water will have to pass through the open- 
ings, E, in the valve piston, this passage causing a cer- 
tain amount of loss in pressure dependent entirely upon 
the velocity of the water through the holes, E. 

Suppose that, when the car is running at 400 feet per 
iiinute, the loss of pressure suffered by the water in 



996 



Steam Engineering 




Fig. 417 



passing through the piston holes, E, is 20 pounds; then, 
if the car is running up, and the pressure of the water 
when it reaches one side of' B is 800 pounds, it will be, on 



Hydraulic Elevators 997 

the other side^ 780 pounds. If the car is running down 
and the water is discharging into the delivery tank^ a pres- 
sure of 100 pounds on the cylinder side of B will corre- 
spond to 80 pounds on the tank side of B ; that is to .say, 
in either case the difference in pressure between the two 
sides of B will be 20 pounds. 

From the construction of the device^ it will be seen that 
the force with which the piston rod^ A^ is moved endwise by 
the difference in the pressure on the opposite sides of B 
is resisted by the springs K^ so that by properly adjusting 
this spring, the car can be made to run at any desired 
speed with the main valve wide open, regardless of the 
magnitude of the load or whether it is running up or 
down. Thus it will be seen that^ when this speed regulator 
is provided^ the car cannot attain an excessive velocity^ 
even if the operator becomes 'confused and opens the main 
valve too wide. 

In passing from either of the inlets^ C or D, into the 
interior of the cylinder^ the water must flow through the 
small holes in the casings P. These holes are drilled on 
spiral lines so that^ when B moves in either direction^ it 
covers the holes one at a time^ thus gradually closing the 
outlet. The end movement of B is transmitted to one, or 
the other of the levers, Gy through rod, A, and the move- 
ment of either lever will compress -spring, K. 

Direct Acting Plunger Type, — A direct acting plunger 
elevator consists of a cylinder set vertically in the ground 
directly under the car, and of length a few feet greater 
than the travel of the elevator car. In this cylinder is a 
plunger of the same length, carrying a car on its upper 
end. The bottom of the plunger is supported by an in- 
compressible body of water, and the car cannot descend 
faster than the water is forced out. 



998 



Steam Engineering 




Fig. 418 
direct acting plunger elevator 



Hydraulic Elevators 999 

The success of this elevator depends largely upon the 
merits of the operating mechanism. In the installation of 
this type of hydraulic elevator it is necessary to sink the 

ihole for the reception of the cylinder to a depth equal 
to the height of the building. Fig. 418 shows the general 

^ arrangement of the Otis direct acting plunger elevator, 

; This illustration is broken at a point between the elevator 
car and the bottom of the elevator shaft in order to reduce 

yits length;, but the part broken away would only show the 
continuation of the guides^, plunger^ operating ropes, etc.; 
all the operating parts of the outfit are shown in the 
illustration. 

In plunger elevators, as the full pressure on the end of 
the plunger acts to lift the car, the diameter of the plunger 
is much smaller than iii the geared types of elevators. The 
pressure used varies from about 140, to 200 pounds per 
square inch and the diameter of the plunger may be from 
5 to 7 inches. The cylinder is made of steel pipe about 
2 inches larger in diameter than the plunger, and the 
hole in the ground is a couple of inches larger than the 
cylinder. It will thus be seen that the hole in which the 
cylinder is placed is not very large, so that it can be bored 
in a manner similar to that employed for driving pipe 
wells. If the subsoil is earth, a steel pipe lining is pro- 
vided which is large enough to receive the cylinder. If 
the hole is drilled in rock, no lining is required. 

For the cylinder, a number of lengths of steel pipe are 
turned true on the ends, threaded in a lathe, and Joined 
by sleeve couplings. The upper end of the cylinder is 
screwed into a cast-iron section which is bored to fit the 
plunger, and is provided with a stuffing-box and a pipe 
connection through which the water enters and passes out 
of the cylinder. The lower end of the cylinder is closed 



1000 steam Engineering 

by means of a suitable cap. The cylinder is coated with 
a protecting paint and when in position, the space bet\^een 
it and the sides of the hole is filled with sand. 

For the plunger^ a number of lengths of steel pipe are 
turned true and well polished. The sections are joined by 
means of long internal sleeves which are so proportioned 
that the transversa strength of the plunger at the joint is 
as strong as at any other point. 

As the elevator car can rise only as high as the plunger 
travels, it follows that when the rise is 300 feet, the cylin- 
der must extend down into the earth several feet more 
than 300, because when the car is at the top of the elevator 
hatchway the bottom end of the plunger must be some dis- 
tance below the top end of the cylinder. Furthermore, it 
is necessary to provide sufficient length of plunger to carry 
the car a short distance above the upper floor, say, two 
feet, in order to avoid running the bottom of the plunger 
too high up in 'the cylinder if the elevator should overrun 
the upper limit of travel. 

The plunger passes through a stuffing-box at the upper j 
end of the cylinder, and is provided with guide shoes at '^' 
the' lower end to keep it in line and central. 

Eef erring to Fig. 418, the car rests upon the upper end 
of the plunger P, and the latter runs down into the cylin- 
der C, the upper end of which projects above the ground 
floor. From the top of the car a number of cables E ex- 
tend upward and over a sheave S and thence down to a 
counterbalance W. This counterbalance serves to reduce 
the pressure required to raise the elevator, and also to 
reduce the compression stress to which the plunger is 
subjected. 

The pipe of which the plunger is made weighs about 22 
pounds per foot, so that a plunger 200 feet long will weigh 



Hydraulic Elevators 1001 

about 4,400 pounds; this is more than the car is likely 
to weigh, the latter ranging between 3,000 and 4,000 
pounds. If the car weighs, say, 3,600 pounds, and the 
plunger 4,400 pounds, the two combined will weigh 8,000 
pounds, and with no counterbalance this weight would have 
to be raised in addition to the load. Consequently the 
plunger would be subjected to a compression stress of 3,600 
pounds plus the load at the upper end, and 8,000 pounds 
plus the load at the bottom, the stress increasing from top 
downward at the rate of 22 pounds per foot. With a coun- 
terbalance weighing 5,000 pounds, the weight raised will 
be reduced to 3,000 pounds plus the load, and as the coun- 
terbalance exceeds the weight of the car by 1,400 pounds, 
it will actually hold up about one-third of the plunger^ 
from the upper end downward, when the car is empty. 

When the car is at the bottom of the shaft the plunger 
is immersed in the water in the cylinder, consequently 
a portion of its weight is balanced by the water it dis- 
places. When the car is at the top of the shaft the 
plunger is out in the air and its weight is not counter- 
balanced to any extent by the water. This being the case, 
the weight lifted will be less when the car is at the bottom 
of its travel than when at the top, the difference being equal 
to the weight of water displaced by the plunger. By prop- 
erly proportioning the weight of the cables E, the load 
j lifted can be made equal at all points, for when tlie car is 
ji at the bottom of the shaft these cables will hang above the 
cCar, and thus will offset a portion of the counterbalance 
L'W, while when the car is at the top of the shaft the cables 
twill hang above the counterbalance W and balance a por- 
tion of the weight of the car. 

The main valve for controlling the movement of the 
jjjfCar is shown at V, and the pilot valve at V. The two 



1002 Steam, Engineering 

valves A and B are the automatic stop or limit valves, A 
being the top limit and B the bottom. The valve A is 
actuated b}^ the rope A" which pnlls np the lever A' and 
thereby closes the valve. This rope moves the lever A' 
through the motion of the elevator car. Looking at the. 
illustration^ it will be seen that the rope A" runs over 
a sheave D mounted on top of the elevator car^ and it can 
also be seen that when the car approaches the upper limit 
of travel^ D begins to put a bend in A" and thereby draws 
up the lever A'; by the time the car reaches the upper 
floor^ A' will be raised enough to close the valve A. By 
this arrangement the valve is closed gradually and the 
car is as gradually brought to a state of rest. 

The valve B is actuated by the rope B" in precisely the 
same manner that A is operated by the rope A". The rope 
B" passes over the stationary sheave D' and under the 
sheave D" located under the car^ and when the latter de- 
scends near enough to the lower floor^ the bend put in the 
rope B" by the sheave D" will raise the lever B' and grad- 
ually close the valve B. 

The pressure water enters through the valve A; hence, 
at the top landing the automatic stop arrests the movement 
of the car by shutting off the supply water. When the 
elevator car descends^ the discharge water passes out 
through the valve B; hence^ the bottom limit valve stops 
the descent of the car by stopping the escape of water 
from the cylinder. 

Construction of Cylinder. — The construction of the upper 
end of the cylinder is shown in Fig. 419. This drawing, 
which is a vertical sectional elevation of the top of the 
cylinder and plunger, also shows the way in which the 
plunger is fastened to the under side of the car, as well 
as the construction of the plunger. For the purpose of 



Hydraulic Elevators 



1003 






^^ 




1 

V/ 


|^__A II 




. 1 



Fig. 419 



1004 Steam Engineering 

reinforcing the plunger, a steel cable B is strung inside, 
both of its ends fastened to a pin A, located some distance 
below the center of the plunger, and the loop or bight, at 
the top of the plunger, is passed around a tightening block 
; this block is arranged so as to be drawn up by the bolts 
0' to put the desired tension on the rope B. The plunger 
D is made of as many lengths of piping of the proper 
size as may be necessary, these being connected by means 
of long internal sleeves C. The plunger sections are turned 
true and highly polished, and the screw threads at the 
ends are made with great accuracy, so as to hold the sec- 
tions in perfect alignment when connected. The threads 
are also made extra long, so that the joints may be as 
strong as the other parts of the pipe. For the purpose of 
making the pipe sections come together perfectly central 
when joined, the center portion of the sleeve is turned true, 
and the ends of the pipe are bored to fit this portion ; when 
the parts are screwed up, the turned central portion of 
the sleeve slides into the bored-out ends of the pipes and 
brings them into line, so that there is no point around 
the joint where one part projects over the other. 

The top of the cylinder is finished ofl with a casting F 
screwed to the top of the upper section of the cylinder 
barrel E. On top of the cylinder cap F is mounted a 
stuffing-box casting G, containing the usual packing space 
T and fitted with a gland G'. The latter is constructed 
so as to form a space surrounding the plunger to hold oil 
which is fed in from the oil cup K. Above this oil reser- 
voir is a recess in which babbitt metal wiping rings I are 
placed for the purpose of scraping the oil off the plunger 
as it moves up, and retaining it in the space in gland G'. 
In Fig. 418 it will be noticed that buffers F are provided 
for the car to rest upon when at the lower floor. Similar 



li 



Hydraulic Elevators 



1005 



buffers are also provided for the counterbalance W to rest 
iipon^ this to prevent running the car up against the over- 
head beams. The construction of the car buffers is shown 
in Pig. 420^ which is an external view of the upper end of 
the cylinder taken at right angles to Fig. 419. The buffer 
consists of a plunger P made of pipe, provided with a 




Fig. 420 

■cast cap P' and a rubber cushion P". The plunger P 
slides within a cylinder C, also made of pipe. Within this 
.cylinder there is a spring that is compressed by the plunger, 
;the lower end of the latter being provided with a tJat head 
to press against the top of the spring. The cylinder C is 
held in position by a side extension P, formed on the top 
cylinder casting P. The nuts P' P" are screwed on the 



1006 Steam, Engineering 

cylinder C, the latter being threaded, and by this means 
the height of the buffer is adjusted. To furnish additional 
support, so that the buffer may not be pushed down, and 
the thread of the nut F' stripped if the car should come 
down unusually hard, a pipe extension E is provided, ex- 
tending down to the floor, or some other firm support. 
These buffers are set so as to be struck and compressed 
every time the car comes down to the lower floor, acting 
to stop the motion gradually. If the car descends at the 
normal speed, the buffer is compressed slightly, just a 
trifle more than is necessary to hold the unbalanced por- 
tion of the weight of the car, but if the car speed in ap- 
proaching the floor is excessive, the buffers will be com- 
pressed farther, and the car will run a few inches below 
the floor. 

Boiler Power for Elevators, — The following very able 
discussion of this subject is presented by Charles L. Hub 
bard in Power: 

"The power necessary to operate an elevator depends 
upon its size, the method of construction and counterbal- 
ancing, the speed, and the efficiency. Placing these con- 
ditions in the form of an equation : 

{W+u)8 

H.P. — ^—^—^ 

eX 33,000 

in which 

Tr= weight of live load, 
i^=unbalanced weight of car, 
/S=speed in feet per minute, 
e= efficiency. 
The elevators in most general use for passenger service 
are of the hydraulic and- electric types: for freight ^o^k, 

some steam and belted elevators are in commission, the 

r 



1 



Dl 



It 



Boiler Power for Elevators 1007 

latter being connected directly with the line shaft in shopg 
and factories. The general method of computing the power 
is the same for both hydraulic and electric elevators, al- 
though they differ to some extent in detail, making it ad- 
visable to consider them separately. 

The live load for a passenger elevator is usually figured 
on a basis of from 60 to 80 pounds per square foot of floor 
space, and the weight of the elevator itself from 100 to 
125 pounds per square foot, which also includes the safety 
device. These figures will be found ample for cars of or- 
dinary construction, but may be exceeded somewhat in 
the case of metal cars of especially massive design. 

Hydraulic Elevators. — It is common practice with ele- 
vators of this type to counterbalance up to about three- 
fourths of the weight of the car. The speed varies from, 
say 200, to 600 feet per minute, 400 feet being about the 
average for office buildings of medium size. The efficiency 
is in the vicinity of 60 per cent. 

In computing the boiler power, it is usually assumed 
'that probably all of the elevators will not be running at 
■ one time at their maximum capacity ; it must be remem- 
bered also that power is required only on the upward trip, 
ias the weight of the car causes it to descend under the 
control of a suitable braking device. When there is no 
definite information at hand, it is customary to compute 
the power necessary to operate all of the elevators at one 
time under full load, and base the boiler power on two- 
thirds of this result. 

Example. — An office building has four hydraulic eleva- 
tors, each having a floor space of 30 square feet. What 
ooiler power should be provided, using the following aver- 
ige data: Live load, 70 pounds per square foot of floor 
mace; weight of elevator, 100 pounds per square foot of 



If 



1008 Steam Engineering 

floor space; speed, 400 feet per minute; efficiency, 60 per 
cent; steam consumption of pumps, 65 pounds per hour 
per horse-power. 

From the foregoing, 

W=30X70X3=6300; 
«=30X100X3X0.25=2250. 
Then for a continuous upward movement with a full load 
the required horse-power would be: 

(6300-^2250) 400 

^ -:=172 horse-power. 

0.60X33,000 
hut, of course, under actual conditions one-half of the 
time is occupied by the downward trips, and the power 
required is therefore only one-half of this, or 86 horse- 
power. Making allowance for stops at the various floors 
and for the time that part of the elevators are idle, it 
may be assumed that it will be sufficient to provide for 10 
per cent of the full time, or 0.70X86=60 horse-power. | 
The steam consumption under the conditions stated would I 
be 60X65=3,900 pounds per hour. 

Assuming 30 pounds of steam per boiler horse-power, 
which may be taken with sufficient accuracy when the pres- 
sure and feed-water temperature are not given, the re- 
quired boiler horse-power will be 3,900-30=130. The 
boiler liorse-power required for running a pump is com- 
puted in a similar manner to that for an engine. 

The rating, or capacity of a pump, however, is usually 
expressed in gallons of water per minute raised to a given 
height, instead of horse-power, as in the case of an en- 
gine. 

The weight of water in pounds per minute multiplied 
by the height in feet to which it is raised, divided by 
33 000 will give the useful, or delivered work of the pump 



t; 



Boiler Power for Elevators 1009 

in horse-power. The friction of the water flowing through 
the passages and valves is so great under ordinary working 
conditions that not much more than 50 per cent of the 
indicated horse-power of the steam cylinders is represented 
by the net useful work. This calls for a large amount of 
steam in proportion to the work done^ as shown by the 
table herewith^ which gives the average steam consumption 
of the ordinary duplex pump. 

TABLE SHOWING AVERAGE STEAM CONSUMPTION OF DUPLEX 

PUMPS. 

Pounds of Steam 
per hour 
Type of Pnmp per delivered 

horse-power 

Simple non-condensing 120 

Compound non-condensing 65 

Triple non-condensing 40 

High-duty non-condensing 30 

The head against which a pump works is the vertical 

distance between the surface of the water in the suction 

reservoir and that in the discharge reservoir. If the 

pump is delivering against a pressure, as in feeding a 

•boiler, the pressure may be reduced to ^^feet head/' by 

•dividing the pressure per square inch by 0.43. 

Electric Elevators. — The type of electric elevators most- 
ly used is the drum. The speeds at which this type com- 
. monly runs may be taken as 300 and 500 feet per minute, 
respectively, for single, and double-drum machines; for 
regular work, speeds above 400 feet are not usually found 
necessary for the average building. 

So far as the necessary power is concerned, the single 
.drum and duplex machines may be considered together. 
The efficiency of these is ordinarily from 50 to 70 per 



,1? 



1010 steam Engineering 

cent, although theoretically the former is the more efficient 
type. In practice it is not customary to count on much 
more than 50 per cent, which gives results on the side of 
safety. 

The method of balancing the electric elevators of the 
drum type differs from that applied to the hydraulic, in 
that the entire vreight of the car plus from 40 to 50 per 
cent of the maximum live load is counterbalanced. From 
this it is evident that with no load the power required to 
pull the car down is that necessary to raise the excess 
counter-weight, which may be taken as equal to one-half 
the maximum live load, and to overcome the friction of 
the machine. When the car is half loaded it is bal- 
anced, and the power required is that to overcome friction 
only. At full load the conditions are the same as for an 
empty car, except the power is required during the up- 
ward trip instead of the downward. It is evident that 
power may be required for both the upward and downward 
trips, depending upon the number of people in the car, 
but it will never be as great at any one time as in the 
case of the hydraulic elevator. 

Example. — Taking the same conditions as in the pre- 
ceding example, what boiler power will be required to 
operate electric elevators of the drum type, having an 
eflBciency of 50 per cent and a speed of 300 feet per minute? 

In this case i^^ the unbalanced weight of the car, disap- 
pears, and the maximum live load is equal to only one- 
half the weight of the people in the car, the other half 
being counter-balanced, so that : 

F=30X70X3X0.5=3150 pounds, 
from which 

3150X300 
■ ■■ 0.50X33,000 ~ 



Boiler Power for Elevators 1011 

If the full load was carried on both upward and down- 
ward trips^ or sufficient of it on the downward trip to 
overbalance the counter-weight and the friction of the car^ 
the conditions would be the same as in the case of the 
hydraulic elevator, that is, power would only be required 
on the upward trip. 

This condition, however, does not hold, especially in the 
case of office buildings, where during the morning hours 
the maximum loads are on the upward trips, with empty 
or nearly empty cars coming down. Under these con- 
ditions the power is practically the same on both trips, 
owing. to the necessity of raising the counter- weight when 
the car is descending. This makes it necessary to treat 
the problem the same as though the machine were raising 
a continuous load. 

Assuming, as before, that a certain amount of time is 

required for passengers to enter and leave the car, and 

that all of the cars will not be running at one time, we 

may take 70 per cent of the above, or 57X0.7=40, as the 

maximum horse-power to be delivered continuously by the 

motor. 

,^ Assuming efficiencies of 80, 90 and 85 per cent for the 

motor, generator and engine, respectively, the required 

indicated horse-power of the engine will be 

40 

'=:62 horse-power. 

0.80X0.90X0.85 

|i The boiler power will, of course, depend upon tlie water 

I rate of the engine. Assuming that a simple non-condens- 

ng engine is employed, requiring 30 pounds of steam per 

ndicated horse-power per hour, 'the boiler power will be 

practically the same as that of the engine, that is, 62 

iOrse-power. The power required to operate duplex eleva- 



1012 Steam Engineering 

tors is practically the same, except a higher speed may be 
allowed/^ 

The method of balancing a screw machine is practically 
the same as for the hydraulic type. The efficiency of this 
machine may be taken as abont 70 per cent. The horse- 
power for driving elevators of this type is calculated the 
\same as for the hydraulic, except for the higher efficiency. 
After the power of the motor has been computed, the 
boiler power may be determined as in the preceding ex- 
ample. 

Freight elevators are computed in the same way, exi-ept 
they are run at lower speeds, and are built especially to 
carry the desired load in each particular case. When ap- 
plying these methods of computation to any particular 
case, the engineer should obtain all the data possible 
regarding the type of machine to be used, the probable 
speed, efficiency, etc., before proceeding; but if any of 
the data are lacking, the average figures already given 
may be used with approximate results. 

QUESTIONS AND ANSWERS. 

661. What are the essential parts of the Otis traction 
elevator ? 

Ans, A traction motor driving sheave, and a pair of 
electrically released brake shoes. 

662. What type of electric motor is used in the Otis 
traction elevator? 

Ans, A slow speed shunt-wound motor. 

663. What is the principal function of the armature 
shaft besides carrying the armature? 

Ans. To support the load. 

664. How, then, is the drum, or sheave driven? 
Ans. By means of projecting arms from the armature, 

that engage: with similar- arms projecting from the drum 



Questions and Answers 1013 

665. Describe the system of safety devices with which 
this elevator is equipped ? 

Ans. There are two groups of switches located respec- 
tively at top and bottom of the shaft, each switch in series 
being opened one after the other by the car as it passes. 
This retards the speed and finally brings the car to stop, 
applying the brake, independent of the operator in car. 

666. Are there any other safeties besides this? 

Ans, Yes — speed governors, wedge clamps for gripping 
the guides, and potential switches. 

667. Describe in general terms the construction of the 
Otis geared traction elevator ? 

Ans. A multi-grooved driving sheave around which the 
cable works. The sheave is mounted upon a shaft driven 
by geared wheels actuated by a right and left hand worm 
cut on the armature shaft. 

668. What advantage is gained by the use of the double 
screw, or worm ? 

Ans. The elimination of all end thrust. 

669. With what kind of brake is this machine equipped ? 
Ans. A mechanically applied, and electrically released 

brake. 

670. What type of motor is used? 

Ans. Compound- wound — speed 800 E. P. M. 

671. When is the series field of this motor used? 
Ans. Only at starting. 

672. Why? 

Ans. To obtain a highly saturated field in the shortest 
ji possible time. 

673. How is a gradual slowing down of speed of car 
obtained with this elevator? 

Ans. By throwing a low resistance field across the ar- 
mature, thus providing a dynamic brake action. , 



1014 Steam Engineering 

674. What kind of current is used for operating elec- 
tric elevators? 

Ans. Either alternating, or direct current. 

675. How is the transmission of current to the motor 
of an electric elevator controlled? 

Ans, By means of an electric magnet controller op- 
erated through the switch in the car. 

676. How may considerable power be wasted in the 
operation of electric elevators? 

Ans. By careless handling — making unnecessary stops 
and starts, or too sudden stops or starts. 

677. Briefly, of what does the mechanism of a hydraulic 
elevator consist? 

Ans. A cylinder and piston with one or more rods con- 
nected to a crosshead which carries the sheaves over which 
run the lifting cables from which the car is suspended. 

678. What moves this piston? 

Ans. Water under pressure admitted by means of suit- 
able valves causes the piston to move from one end of the 
cylinder to the other, and back again. 

679. How is this motion transmitted to the elevator 
car? 

Ans. By means of the sheaves mounted on the cross- 
head which carry the lifting cables. 

680. In what position is the cylinder placed? 

Ans, Either vertical alongside the hatchway, or hori- 
zontal in the basement of the building. 

681. How are the valves of a hydraulic elevator op- 
erated ? 

Ans. In some cases by a hand rope passing through 
the car and over small sheaves at the top and bottom of 
the hatchway, and connected with the main valve in the 
basement. By pulling this rope down the valve is opened. 



Questions and Answers 1015 

and the car will ascend, while pulling the rope np will 
cause the car to descend. 

G82. What safety devices are attached to this type of 
elevator? 

Ans. Two balls are attached to the hand rope^, one near 
the bottom, and the other near the top. These balls come 
in contact with the top, or bottom of the car, according 
as it is going np or coming down, and being carried along 
they, of course move the cable, thus actuating the valve, 
bringing the car to a stop. 

683. Is this device safe, and automatic? 
Ans. It is. 

684. Mention another safety device connected with 
hydraulic elevators. 

Ans. Safety clamps under the control of a speed limit 
centrifugal governor which causes the clamps to grip the 
guides and thus hold the car. 

685. How is this safety governor operated? 

Ans. By means of a small cable connected with the car 
and moving with it, which passes over the sheave pulley 
of the governor. 

686. Why are some elevator pistons fitted with two pis- 
ton rods? 

Ans. To prevent the piston, and crosshead from turn- 
ing or twisting, and also to strengthen the construction. 

687. What other methods are used for manipulating 
the water valve, besides the one already described? 

Ans. Eunning ropes^ and standing ropes, either of 
which may be operated by means of a lever, or wheel in 
the car. 

688. Do these devices directly operate the main valve? 
Ans. No. They operate a small valve called the pilot 

valve. 

689. What is the function of the pilot valve? 



1016 Steam Engineering 

Ans^ Whm opened it admits the pressure water to a 
small cylinder with piston connected to the main valve 
stem. This actuates the main valve, which in turn, by its 
movement, closes the pilot valve. 

690. Upon what does the amount of opening given the 
pilot valve, and consequently the main valve depend? 

Ans. Upon the distance the lever in the car is moved 
from central position. 

691. What is meant by central position of lever? 
Ans, That position in which there is no flow of water 

either into or out of the cylinder, and the car is moving 
only by its momentum. 

692. What is the result of moving the lever too quickly 
to central position when the car is moving at a high 
rate of speed? 

Ans, The motion of the car will be arrested with a 
sudden jerk. 

693. How many kinds of horizontal hydraulic elevators 
are in use ? 

A71S, Two. One is the pushing, and the other the 
pulling type. 

694. Describe the action of the pushing type? 
Ans. The car being at the bottom, the pressure water 

is admitted behind the piston which then moves, pushing 
the crosshead and cable sheave and lifting the car. 

695. Describe the action of the pulling type? 
Ans. It is the opposite of that just described. 

696. Is there much difference. in the valve mechanism 
of the horizontal, and vertical types of hydraulic elevators ? 

Ans. Very little except a few minor details. '^^ 

697. What is meant by a double-deck machine? ^^ 
Ans. Where the floor space is restricted two, and some- 
times three or four machines are mounted one above the fP* 
other* 



lei 



Questions and Answers 1017 

698. What water pressure is usually carried in operat- 
ing the types of hydraulic elevators that have hitherto 
been described? 

Ans. Pressures not exceeding 200 Ibs.^ the average being 
150 lbs. per square inch. 

699. Are any higher pressures than this being used for 
operating hydraulic elevators? ^ 

Ans. Yes. Pressures of 700 to 800 lbs. and higher. 

700. Why are such high pressures used? 

Ans. Owing to increased height of buildings, and the 
demand for high car speed. 

701. What advantage, other than high speed, is gained 
by the use of high pressure elevators? 

Ans. A reduction in the size of the valve mechanism^ 
piston areas and piping. 

702. Mention another advantage in connection with 
the high pressure system? 

Ans. A reduction in the loss by friction of the water 
passing through the pipes, owing to reduced areas. 

703. What is the percentage of loss due to this cause? 
Ans. In low pressure machines from 10 to 30 per 

cent, and in high pressure machines from 5 to 6 per cent. 

704. Describe in general terms the construction of the 
cylinder and piston of a high pressure machine. 

Ans. The cylinder area is reduced to about one-eighth 
that of the low pressure type, and the piston is a solid 
plunger. 

705. How is the pressure maintained? 

Ans. The pump forces water into the lower end of the 
accumulator, an air-tight tank, which is also weighted. 
Prom the accumulator a pipe runs to the main valve. 

706. Describe in general terms the construction and 
operation of the direct-acting plunger elevator. 



1018 Steam Engineering 

Ans. A cylinder is set vertically in the ground under 
the center of the car^ and the length of it is slightly 
greater than the travel of the car. In this cylinder is a 
plunger of the same lengthy which carries the car. "Water 
under pressure is forced into the cylinder and thus lifts 
the car, and allowed to run out at the top when the car 
descends. The cylinder is about two inches larger in dia- 
meter than the plunger, and is always full of water. 

707. What is the usual diameter of the plunger? 
Ans, 61/^ to 7 inches. 

708. How is it constructed? 

Ans, Of lengths of highly polished steel pipe, joined 
together with an internal sleeve, and having its lower end 
closed. 

709. What pressure is ordinarily used on this type of 
elevator? 

A71S, 150 to 200 lbs. per square inch. 

710. How is the top of the cylinder arranged? 

Ans, With a packing gland through which the plunger 
moves up and down. 

711. What types of elevators are in general use for 
passenger service? 

Ans, Electric and hydraulic' 

712. How is the capacity of a pump usually expressed? 
Ans. In gallons of water per minute raised to a given 

height. 

713. What is meant by the head under which a pump 
works ? 

Ans, The vertical distance between the surface of the 
water in the suction reservoir, and that in the discharge 
reservoir. 



Electricity for Engineers 

Electricity is an invisible agent, the exact nature of 
which is not very well known, although the laws governing 
its action, the methods of controlling it, and the effects 
produced by it are becoming well known. It is necessary 
to assume in the start that it is of such a nature as to 
be susceptible of possessing quantity. We may, and do 
use terms to designate definite and definable quantities 
of electricity without being able to say just what is meant 
by the word itself. Eor instance, referring to an electric 
current, it is the transfer of definite quantities of elec- 
tricity along a conductor, just as .in a current of water^ 
gallons, or cubic feet are transferred through a pipe. But, 
the idea of large quantities of electricity being stored up 
in receptacles for future use, in a similar manner to water, 
cannot be followed except in a limited sense, as for in- 
stance, in the case of storage batteries. One of the most, 
if not the most important generalizations ever made in 
physical science is the doctrine of the conservation of 
energy, or as it is sometimes called, the doctrine of the 
indestructibility of energy. This doctrine teaches that the 
total quantity of the energy in the universe is unalterable; 
that is, if energy is expended or disappears in one form, 
it must reappear in another form. A simple analogy will 
serve to make this matter plain: Suppose a man, by means 
of a rope passing over a pulley, raises a 100-pound weight 
one foot above the surface of the earth, which means 100 
foot pounds of work, or energy. Now, the man has ex- 
erted, or put forth that amount of energy, and so far as 

1019 



i 



1020 Steam Engineering 

he is concerned, he no longer possesses it. Apparently it 
has been blotted out of existence — annihilated. But this 
annihilation is only apparent for the reason that energy is 
capable of existing in two forms, viz., kinetic, and potential 
or stored energy. While the muscular force of the man is 
being expended in actually doing work raising the 100- 
pound weight, it is in a condition called kinetic energy. 
While the weight is held in position at a distance of* one 
foot above the earth, it is producing a stress, or pull on the 
rope, and is in the condition of stored or potential energy. 
If the rope is suddenly loosed, the weight will descend, and 
during this descent will put forth an amount of kinetic 
energy exactly equal to the 100 pounds of work or energy 
that was expended in raising it one foot from the ground. 

Much of the mystery that exists in the minds of many 
persons concerning electricity will be unraveled and made 
clear when it is understood that, like all other natural 
forces, electricity is only one of the many forms in which 
energy manifests itself. Like all other forms of energy, 
electric energy, or the power that electricity possesses of 
doing work, is fixed and determinate. 

An electric source, whether it be a voltaic cell, or a dyna- 
mo, is capable, under given conditions, of producing a 
certain quantity of electricity. In the case of the dynamo 
being operated by the steam-engine, the heat energy stored 
in the fuel by the sun^s rays, is made to do a certain 
amount of work, through the medium of the boiler, the 
steam, and the engine, and this work or energy is simply 
changed by the dynamo into the form of electric energy, 
and passes on out through the circuit to do useful work in 
the way of power, lighting, etc. 

When electricity is caused to flow between any two 
points in a circuit, the amount of work it can perform is 



Electricity for Engineers 1021 

equal to the amount of electricity that passes^ multiplied 
by what is called the difference of potential through which 
the electricity falls or moves. 

When work is done on a quantity of water by forcing 
it into a reservoir at a higher level than that from which 
the water has been raised;, the amount of work done can 
be measured in foot-pounds by the quantity of water in 
pounds so raised;, multiplied by the difference in level 
through which it is raised in feet. While it is not the 
intention to suggest that electricity is a fluid, yet it pos- 
sesses many of the properties of a fluid;, so that the amount 
of work electricity is capable of doing depends on the 
quantity of electricity moved^ as well as on the difference 
of the electric level or potential through which it has been 
raised. 

The unit of quantity of a water current may be taken 
as a cubic foot or a cubic inch. In electricity the practical 
unit of quantity is a certain quantity of electricity called 
a coulomb. In measuring this quantity of electricity;, ref- 
erence must be had to certain other electrical units, i. e., 
the amperC;, the volt and the ohm. 

The ampere is the name given to a practical unit of 
electric current^ and is such a rate of electric flow as is 
capable of transmitting a quantity of electricity equal to 
one coulomb per second. A current of electricity equal 
to one ampere will flow through a circuit whose resistance 
is one ohm^ when acted on by an electromotive force or 
pressure of one volt. An ampere is approximately such a 
current of electricity that is capable of depositing 1.118 
milligrammes of silver per second from a specially pre- 
pared solution of silver nitrate. 

The volt or practical unit of electromotive force is an 
electromotive force or pressure that is capable of causing 



1022 Steam Engineering 

the flow of an electric current of one ampere through a 
circuity the electric resistance of which is equal to one ohm. 

The ohm is the practical unit of electric resistance. It 
is the resistance that would limit the flow of electricity 
under an electromotive force of one volt to a current of 
one ampere^ or to a discharge of one coulomb per second. 
It is equal to the resistance of a column of pure mercury 
one square millimetre in area of cross section and 104.9 
centimetres in length. 

A coulomb is the practical unit of electric quantity. It 
is the quantity of electricity that would pass in one second 
through a circuit carrying a current of one ampere. 

Electric energy can be measured in terms of electric 
power or rate of doing work. A careful distinction should 
be made between work^ or the product of force by the dis- 
tance through which the force acts^ and power or rate of 
doing work. As we have already seen^ the unit of work 
is called the foot-pound. The unit of power or rate of 
doing work^ or^ as it is sometimes called/ the unit of 
activity is equal to the foot-pound per second^ or foot- 
pound second. 

The amount of work electricity is capable of doing is 
equal to the quantity of electricity that flows, multiplied 
by the difference of level or potential through which it 
flows. This is the volt-coulomb or joule. The amount of 
electric activity or work per second is equal to the volt- 
ampere or the watt. 

THE WATT. 

The volt-ampere or watt is equal to the power developed 
when 44.25 foot-pounds of work are done per minute, or 
0.7375 foot-pounds per second. 



Magnets 1023 

If the ampere is replaced by the symbol C, the volt by 
the symbol E, the watt by the symbol W^ and resistance 
by E, then, CXE=W, and C^X^=W, 

The square of the current multiplied by the resistance 
equals watts; and the square of the voltage divided by the 
resistance equals watts, thus: E2-f-E=W, expressed in 
figures as follows: 

First. An electromotive force or pressure of 10 volts 
and a current of 20 amperes equals, 

10X^0=200 watts. 

Second. A current of 10 amperes and a resistance of 
80 ohms equals, 

10X10X30=3000 watts 

Third. An electromotive force of 10 volts, and a re- 
sistance of 20 ohms equals, 

10X10-f-20=5 watts 

MAGNETS. 

The natural magnet is a mineral consisting of a com- 
bination of iron and oxygen, and its composition is indi- 
cated by the chemical formula Fcg O4. The mineral is 
called magnetite, and it is attracted by the magnet just 
as iron is, only not so powerfully. 

Some samples of magnetite attract iron. These are 
natural magnets known to the ancients as the lodestone. 

The permanent magnet is a piece of steel which has been 
charged with magnetism, and retains it. It attracts iron, 
its ends having the strongest attractive power, it tends to 
point north and south, the same end always tending to- 
wards the same pole. The poles of the magnet are thus 
determined, and are designated the north pole, and the 
south pole. 



1024 Steam Engineering 

The north poles of two magnets tend to repel each j . 
other^ and the south poles influence each other in the same 
manner. But the north pole of one magnet attracts the 
south pole of another; like repels like^ and unlike attracts 
unlike. 

There are various methods of charging magnets. One 
process is as follows: Lay a bar of steel on a table^ and 
with one pole of a permanent magnet, stroke the steel 
bar from center to end, always lifting the magnet clear of 
the bar on the return stroke. This is repeated a number 
of times, and then the same operation is applied with the 
other pole of the magnet to the other half of the bar. The 
end of the bar stroked with the north pole of the magnet 
will be a south pole, and vice versa. The stroking may be 
done for both halves of the steel bar by using two mag- 
nets at the same time. The north pole of one magnet 
and the south pole of the other are brought almost to- 
gether at the center of the bar, and simultaneously moved 
out to the ends, always lifting them clear of the bar on 
the return stroke, and the stroking is repeated. 

The U-shaped Magnet, or as it is usually called, the 
horseshoe magnet, may be charged or magnetized by strok- 
ing with another horseshoe magnet from near the bend to 
the ends, or from the ends to the bend. A piece of iron 
should be laid across the ends during the process. 

The Electro-Magnet, — ^^If a bar of iron be surrounded 
by a coil of wire through which an electric current is 
passing, it will become charged magnetically, and will 
attract iron. 

LINES OF FORCE. 

The passing of a current of electricity produces a con- 
dition of more or less strain, or whirl in the ether, and 



Field of Force 1025 

unless distorted in some way the locus or locality of the 
condition is symmetrical with respect to the current. This 
locality is called the field of force. It affects iron^ and 
is traced, and may be located by its effects upon the 
needle of the compass, or upon iron filings. It is by virtue 
of the field of force that every dynamo electric generator, 
and every electric motor works. A needle held near a 
magnet is attracted because of the field of force. In the 
ease of the mariner^s compass, the needle is influenced by 
the earth^s field of force. A coil of wire rotated within 
any artificial field of force, will generate electromotive 
force, and it is due to this principle that the revolving 
armature of a dynamo, or more properly speaking, a gen- 




Fig. 421 
lines of fokce surrounding an active conductor 

erator, produces currents and potential capable of doing 
work of various kinds. We can thus see that the electric 
current in its effects is a very real and tangible thing, 
although in theory it is somewhat imaginary. The mag- 
net is the most familiar producer of lines of force, and the 
polarity, or direction of these lines is fixed by assuming 
that they pass through the steel of the magnet from its 
south pole to its north pole, and issuing from the latter, 
curve around through space and return to the south pole. 
The direction taken by the electric current is fixed by 
assuming that when produced by a galvanic battery, it 
starts from the copper electrode, and passes through the 
outer conductor, to the zinc plate, and the lines of force 



1026 Steam Engineering 

surrounding the conductor will be in planes at right angles 
to it;, and will form closed lines around it. These lines 
may be circular or otherwise^ and their polarity^ or in other 
words^ their direction of rotation^ may be expressed by 
saying that it is opposed to the motion of the hands of a 
watch or clock^ assuming that the current is coming toward 
a person, and corresponds to the motion of the clock hands 
when going away from the person. In the first case, the 
polarity is anti-clockwise, and in the second case, it is 
clockwise. Figs. 421 and 422 will serve to illustrate the 
principle governing the action of these lines, the arrows 



//,{, 






Fig. 422 
lines of force surrounding an active conductor 

in Pig. 421 indicating the direction of the current, while 
Tig. 422 may be called an ^^end view.^^ 

The smoke rings often produced from the smoker^s pipe 
are good representations of the whirling motion of these 
lines of force. A conductor that is swept through a field 
of force in such a direction as to cut the lines of force, has 
electromotive force impressed upon it, and if the ends 
of the conductor are connected so as to form a closed 
circuit, a current of electricity will pass through it. The 
electric current may therefore be considered as electricity 
in motion, and the line of force with absolutely fixed di- 



Field of Force 1027 

rection may be assumed to have a whirling motion around 
its axis^ which latter does not change, see Figs. 421 and 
422. 

When a current passes through a spiral conductor, as 
shown in Fig. 423, in the direction indicated by the small 
arrows, the direction of the lines of force produced will 
be as indicated by the large arrow ; but if, instead of pass- 
ing through the spiral conductor, the current should pass 
through a conductor occupying the position of the large 
arrow, then the lines of force would follow the direction 
of the small arrows. 




Fig. 423 • ' 

direction of lines of force produced by a circular current 
There are, then, surrounding a conductor carrying a 
current of electricity, an infinite number of lines consti- 
tuting in fact a volume of force, and the strength of this 
volume, or field, varies with its nearness to, or distance 
from the conductor. 

In practice, the field near the conductor is the only 
\ portion strong enough to play any part in useful work, and 
I this strength or density is estimated by the relative num- 
i ber of lines of force in a given cross-sectional area of the 
1 field. 



1028 Steam Engineering 

THE MAGNETIC CIRCUIT. 

A fundamental difference exists between the electric, 
and the magnetic circuit. By a constant electric current 
passing upon its circuity energy is developed^ and energy 
must be expended to maintain it; but the lines of force 
are maintained in their circuit without the expenditure 
of energy. The entire course taken by lines of force must 
be a closed curve, either a circle, or an ellipse. In the 
field of force maintained by the horseshoe magnet, or other 
shaped magnets, the lines of force pass through the mag- 
net, and also through the space surrounding it, and their 
path may approximate a circle, or an ellipse, or be a com- 
bination of lines and curves, but this path must be con- 
tinuous. A straight line of force, or a line of force ex- 
tending into space without limit, is impossible. For the 
passage of an electric current, a conductor forming a closed 
circuit is required. This conductor may be any form of 
matter, although a distinction is to be made between good 
and bad conductors. For the passage of the magnetic cir- 
cuit or lines of force no such arbitrary requirement exists, 
although a distinction is also to be made, as, for instance, 
air, or a vacuum are the worst conductors, while iron is 
the best. There is in fact very little difference in sub- 
stances as regards their ability to pass lines of force, with 
the exception of iron which has over three hundred times 
the power of passing lines of force that air has. The 
electric current passes through a conductor in intensity 
proportional to the electromotive force urging it. The 
magnetic circuit passes through air or a vacuum in pro- 
portion to the magneto-motive force urging it. 

In order to create new lines of force, or in other words 
to build up a field of force, new energy must he expended ; 



Field of Force 1029 

but when the field of force is once built up, no energy is 
required to maintain it, as the full current passing through 
the circuit unopposed, except by resistance, maintains the 
field of force without the expenditure of energy. This con- 
dition is similar to the carrying of a weight up a fiight 
of stairs. Energy is expended in carrying the weight to 
the top of the stairs, but when there it is maintained there 
without requiring the expenditure of energy, and the 
energy exerted in bringing the weight up-stairs would 
seem to have disappeared, or to have been annihilated. 
But this is not the case. On the contrary, the energy is 
stored in the weight, and will be again expended when the 
weight is taken down. So also the energy expended in 
building up a field of force is stored there in the form of 
electric potential, and may be expended in the production 
of kinetic electric energy when the field goes out of ex- 
istence. This disappearance of the field occurs when the 
electric current ceases, the lines of force disappearing at a 
more or less rapid rate, and in doing so they develop for- 
ward electromotive force of the same polarity as the orig- 
inal current, thus forcing additional current through the 
line. 

The leading characteristics of the field of force may be 
summed up under the following general headings : 

First. Energy is expended in building up a field of 
force. 

Second. No energy is expended in the maintenance of 
a field of force. 

Third. Energy is expended in the destruction of a field 
of force. 

Fourth. A field of force, then, must be, and is the loca- 
tion of potential energy. 



1030 



Steam Engineering 



Electro-Magnetic Induction, — If we take a coil of wire, 
Fig. 424^ and rapidly thrust a magnet into it, we shall 
observe a certain deflection of the galvanometer needle 
shown with it. This deflection continues only while the 
magnet is in motion. After we have inserted the magnet 
and it has come to rest the galvanometer needle will return 
to its normal position. When we withdraw the magnet the 
deflection of the needle will be in the opposite direction. 
If the magnet is inserted or withdrawn with a very quick 




Fig. 424 



motion, the deflection will be considerable. If the magnet 
is very slowly inserted, or withdrawn the deflection will 
hardly be noticeable. The same phenomena will occur if 
instead of moving the magnet, we hold it stationary and 
move the coil, or if both of them be moved towards or from 
each other. The deflection of the compass needle indicates 
that a current of electricity is passing along the wire, and 
the experijnents above described show exactly how currents 
of electricity are produced in dynamos. 



Field of Force 



1031 



While a natural magnet will maintain a field of force in- 
definitely without the expenditure of energy, it is necessary 
that energy be indirectly expended in maintaining the field 
of a dynamo^ for the reason that an electro-magnet is pre- 
ferred to a natural magnet in such a machine^ because by 
its use the dynamo may be made much smaller and lighter. 

An electro-motive force is induced by rapidly cutting 
lines of force^ that is^ by moving either a magnet over a 
wire or a wire over^ or near a magnet. The current in turn 
is the result of this electro-motive force acting in a closed 
circuit. A bar of iron becomes an electro-magnet if we 






'1 ^m 



' / / / 




wind about it a few turns of wire and cause a current of 
electricity to flow along the wire^ Fig. 425. The magnetism 
is conceived to consist of lines of force, which leave the 
bar at one end and enter it at the other, the direction of 
these lines depending upon the direction in which the cur- 
rent circulates about the bar of iron. The number of these 
lines of force depends upon the number of ampere turns in 
the iron bar and on the diameter, length, and quality of the 
iron bar. 

The meaning of the word ampere as used in electric 
practice has already been defined. 



1032 Steam Engineering 

Ampere turns is a term used to indicate the magnetizing 
force ; it is the number of turns of wire on a magnet mul- 
tiplied by the current in amperes flowing through these 
turns of wire. 

Haskins, in Electricity Made Simple, explains it in this 
manner: ^^If, for instance^ we have a current of one am- 
pere flowing through a single turn of wire around a bar of 
soft iron, and we have developed enough magnetism to lift 
a keeper or other piece of iron, weighing one ounce, then 
with one-half the amount of current and two coils around 
the bar, we would obtain the same result, and with three 
turns of wire we would require but one-third the current 
to develop the same lifting power in the bar or magnet/^ 

The law of magnetic flow is very much the same as the 
law of current flow. If the iron bar is of low magnetic re- 
sistance, the flow will be quite great ; if of high resistance, 
the flow will be small. 

Lines of force can also be shunted just as a current of 
electricity can ; that is, they will follow the path of lowest 
resistance just as a stream of water or a current of elec- 
tricity will. 

Faraday's law of induction is as follows : ^^When a con- 
ductor is moved in a magnetic field so as to cut the lines 
of force, there is an electro-motive force impressed on the 
conductor in a direction at right angles to the direction of 
the motion, and at right angles also to the direction of the 
lines of force.'' 

Foucault or Eddy Currents. — If a conductor should be 
so moved in a magnetic field that the number of lines of 
force passing through it at an angle with its direction of 
motion vary, a current will be produced within it. This 
current will circle, or eddy around within the conductor, 
and will absorb energy, and expend it in Heating the me- 



The Dynamo 



1033 



tallic body of the conductor. These local currents are 
called Foucault or eddy currents, and are a hindrance, 
rather than a help to the generation of useful currents. 



DYNAMO-ELECTRIC GENERATORS. 

The dynamo is a machine for transforming mechanical 
energy into electrical energy — mechanical energy is re- 

1 




Fig. 426 



quired to operate the mechanism for changing field and 
armature relations, and this energy is absorbed by the dy- 
namo, and electric energy is produced in its stead. The 
easiest way to comprehend the principles of the dynamo is 
to follow up its construction from the most simple type, to 
one of the more complicated forms. Dynamos are classi- 
fied into two grand divisions, viz., alternating (A. C.) dy- 
namos, and direct current (D. C.) dynamos. The A. C, 



1034 Steam Engineering 

dynamo produces a current that reverses its direction of 
flow periodically^ in practice from twenty times and up- 
ward per second. The D. C. dynamo produces a current of 
unchanging direction. 

The principal constituent parts of a dynamo are the ar- 
maturC;, consisting of a core and windings, the field con^ 
sisting also of core and windings^ the collecting rings^ or 
commutator^ and brushes. The armature and field vary 
in construction^ their windings vary in system, and from 
these variations, many different varieties of dynamos are 
constructed. 

Eig. 426 is an elementary sketch of a D. C. dynamo. 

The wire a represents the armature, and we have also the 
iron bar, and the coil of wire wound on it and, for the pres- 
ent, we may consider the battery B as the source of the 
current which produces the magnetism or lines of force in 
the iron bar. The battery current magnetizes the iron bar 
(which in dynamos is known as the field magnet) and pro- 
duces the lines of force indicated by arrows. 

These lines of force leave the field magnet of the dyna- 
mo at the north pole marked N, and pass through the air- 
gap, and armature into the south pole marked S. As we be- 
gin to move the wire or armature, it cuts through these 
lines of force and begins to generate an electro-motive 
force, which in turn will cause the current- to flow if the 
circuit is closed through a lamp or other device. 

This current reverses in direction as the wire a passes 
from the influence of the south pole into that of the north 
pole, and the brushes B' and B", which transmit the current 
to the outside wires, are so set that they change the con- 
nection of the wire a at the time that it passes from one 
pole to the other. By this means the current in the external 



The Dynamo 



1035 



circuit is kept constant in direction^ although it alternates 
in the armature. 

The faster we turn the wire or armature^ the greater 
will be the electro-motive force generated. Instead of 
using only one wire^ as in. Fig. 426, we may take many 
turns before bringing the end out, and in so doing obtain 
the well known drum armature, or, by a slightly different 
method of winding, the gramme ring armature. Fig. 427. 




Fig. 427 



Here we have many wires cutting the lines of force at once 
and the electro-motive force with the same number of rev- 
olutions of the armature is correspondingly increased, and 
the more turns of wire we arrange to cut those lines of force 
per second the greater will be the E. M. F. Instead of pro- 
viding more wire or increasing the speed of the armature 
we can increase the magnetism, or number of lines of force, 
by sending more current through the fields, that is increas- 
ing the ampere turns. 



1036 



Steam Engineering 



If we wish to reverse the current flow we can do so by re- 
volving the armature in the opposite direction, or by re- 
versing the current through the fields. 




Fig. 428 
use of collecting or slip rings 



D ^A. B 




LAJSXPS 

Fig. 429 
the simple alternating current dynamo, 
positive 



BRUSH M IS 



Elementary Idea of an Alternating Current Dynamo, — 
If instead of the brushes B' and B" as shown in Fig. 436, 
we collect and transmit the current to the outside circuit 



The Dynamo 



1037 



by means of collector rings as shown in Fig. 428^ we will 
then have an alternating, instead of a direct, or constant 
current as before mentioned. 

In Figs. 429 and 430 are shown two positions of the 
loof) on the armature of an alternator. The collector rings 
are insulated from the shaft and each other by mica. The 
terminals of the loop are soldered or riveted (sometimes 




Fig. 430 

the simple alternator, shows coil at one-half a revolution 

FROM Fig. 429. brush m is now negative 

both) to the rings, and current is led to the external circuit 
containing the lamps by stationary strips of copper which 
form a sliding contact with the rings. 

Eeferring to Fig. 429 it will be seen that during the 
first half of the revolution of the loop ABCD, the direction 
of the electro-motive force in AB is from B to A, and in 
CD is from C to D. 



1038 



Steam Engineering 



The current flows from the brush M to the lamps so that 
M is positive. 

Eeference to Fig. 430 shows that the wire in front of the 
S-pole is still positive;, but that it is now the wire CD in- 
stead of AB, so P is the positive brush for the second half 
of the revolution. There are two reversals of the current 
per revolution. 




Fig. 431 
simple d. c. generator. at this instant the brush m is 

positive 

The number of alternations per minute is the speed in 
revolutions per minute multiplied by the number of poles. 
The number of cycles is found by multiplying the speed 
in revolutions per second by the number of pairs of poles. 
The number of cycles is usually spoken of as the frequency 
of the alternator. 



The Dynamo 



1039 



The usual frequencies are for' power 25^ for motor cir- 
cuits;, and arc lamps ^^, and for incandescent lighting 133. 

The Direct Current Generator, — In Fig. 431 is shown 
a loop and a two part commutator of a direct current gen- 
erator. 

Since the wire AB is moving down past a S-pole^ the 
current flows from B to A and out of the brush M, which 




Fig. "432 

» SIMPLE D. C. GENERATOR. THE ARMATURE HAS MADE HALF A 
REVOLUTION, BUT BRUSH M IS STILL POSITIVE 

is called the positive brush. In wire CD the current flows 
from C to D^ making P the negative brush. 

After half a revolution the wire CD is over where AB 
waSj and is now delivering the current towards the external 
circuit instead of away from it; iut CD is now connected 
through its commutator bar to brush M instead of to P so 
that the brush M is still positive, (See Pig. 432.) 



1040 Steam Engineering 

This arrangement of commutator bars and brashes per- 
forms the duty of connecting the brush M to that part of 
ihe winding, and only that part which is moving down in 
front of a S-pole. As long as the wire AB moves up in 
front of a N-pole the commutator connects it to brush P, 
but as soon as it moves down in front of a S-pole it is im- 
mediately disconnected from P, and a connection made 
with M. 




Fig. 433 

ait abmature coil connected to a two-part com mutator, so as 

to deliver direct current 

The two brushes are placed as shown in Fig. 434. In 
ihis case the alternating electro-motive force will be re- 
"versed or commuted at the proper instant, and there will 
be a one direction electro-motive force impressed on the 
outside circuit. The split ring is called a commutator, and 
is formed of alternate sections of conducting and non-con- 
ducting material, running parallel with the. shaft with 
which it turns. It is placed on the shaft of the armature 
so that it rotates with it, as shown in Fig. 437. The 
brushes press upon its surface and collect the current from 



The Dynamo 1041 

the bars. (See Fig. 438.) The function of the commu- 
tator as before stated, is to change the connections of the 
armature coils from the + or positive to the negative or — 
side of the circuit at the time at which the coil connected 
to the bar under the brush passes from the influence of one 
pole piece into that of the other. This is the time at which 
the current in the coil reverses in direction, and is called 
the neutral point. If we consider, for the sake of simplic- 
ity, an armature having only one turn of wire on it, as Fig. 
426, there will be a time while the coil is in the position 
indicated by dotted lines at c and d when no current is 
being generated. The brushes on any dynamo should al- 




FiG. 434 

CROSS SECTION OF SIMPLE COMMUTATOR. BLACK REPRESENTS 
COPPER ; WHITE SPACE IS MICA INSULATION 

ways be set at this point, for this is the point of least spark- 
ing. In actual practice all commutators have quite a num- 
ber of bars and it is impossible to avoid, in passing under 
the brushes, that at least two of them are in contact with a 
brush at the same time. If a brush did leave one bar before 
it touches another, the current would be entirely broken 
for that length of time, and much sparking would result. 
The nature of all armature windings is such that while the 
brush is in contact with the commutator bars it short cir- 
cuits that coil between them. This is the main reason why 
,|the brushes must be kept at a point at which the coil which 
is short circuited generates no current. 



1042 Steam Engineering 

Although the electro-motive force generated in one coil 
of a d3Tiamo is very weak, the resistance of the ^^short cir- 
cuit^^ formed by the dynamo brush is also very weak and 
therefore the current may be quite strong. This current is 
the main cause of sparking in dynamos. The num.ber of 
bars constituting a commutator depends upon the winding 
of the armature, and the number of coils grouped thereon. 
By increasing the number of coils and commutator sections 
the tendency to spark at the brushes is decreased, and the 
fluctuations of the current are also decreased. However, 




Fig. 435 
a single coil armature of many turns 

there are many reasons against making the number of bars 
on a commutator very great. Increasing the number of 
bars in a commutator increases the cost of manufacture, 
and in sm.aller dynamos, if the number of bars be increased 
beyond a certain extent, each bar becomes so thin that a 
brush of the proper thickness to collect the current from 
the commutator would lap over too many bars of the com- 
mutator at one time. Each commutator bar should be of 
the size that will present sufficient metal for the carrying 
capacity of the current generated in the coil to which it is ' 
connected. Different builders of dynamos have different 
ideas as to the number of amperes that may be carried per 



i 



i 

mi: 
end 



The Dynamo 



1043 



square inch in a commutator bar, but where a commutator 
is made of 95 per cent, copper it is usual to allow for each 
100 amperes a commutator bar surface of IVo sq. in. 
The method of electrical connection between the com- 




FiG. 436 

AN ARMATURE COIL OF MANY TURNS SHOWING HOW THE INDUCED 
E. M. F. OF EACH TURN ADDS ITSELF TO THAT OF OTHER TURNS 

mutator bar and the coil of the armature varies in different 
designs. Some builders solder the terminals of the coils 
to the commutator bars; others bolt the terminals of the 
coils to the bars; and some makers use hard drawn copper 




Fig. 437 
and "form^^ the armature coil in such a manner that both 
3nds of the coil become commutator bars, making the coil 
continuous from one end of the commutator bar to the end 
)f the diametrically opposite commutator bar. 
To increase the electro-motive force. The greater the 



1044 



Steam Engineering 



field strength, and the higher the speed the greater the 
electro-motive force. 

When the speed has been raised until the surface of the 
armature is traveling at the rate of 3,000 ft. per minute* 
no further increase is made, lest the bursting stresses be- 
come too great. 




Fig. 43S 

SEPARATELY AND SELF-EXCITED SERIES DYNAMO. 

In order to further increase^ the electro-motive force 
more turns or loops of wire must be wound on the arma- 
ture. A coil of 16 turns as in Fig. 435 will give an electro- 
motive force 16 times as great as a coil like Pig. 426. Eef- 
erence to Fig. 436 will serve to make this plain. 

Suppose the direction of rotation to be the same as the 



*This is called the Peripheral Speed of the armature 
and is calculated by this rule : 

P. S. equals 3.1416 x D x E. P. M. where D is the di-i 
ameter of armature in feet and E. P. M. is the revolution; 
of the armature per minute. 



The Dynamo 



1045 



hands of a watch when viewed from the commutator end of 
the machine ; then the electro-motive forces induced in the 
successive portions of the wire will be as shown by the ar- 
rows^ and will add to each other impressing a high electro- 
motive force on the brushes. These turns of wire are said 
to be in series. 




Fig. 439 

drum winding on a drum core. four coils and four 
commutator bars. for direct current 




Fig. 440 
diagram of fig. 439 



Any betterment of the magnetic conductivity of the frame 
of the machine will increase the electro-motive force; by 
producing a greater flux per pound of copper on the field 
magnets. Hence the winding of the armature inductors 



1046 Steam Engineering 

(wires) on a core of very softest iron is an economic ne- 
cessity^ resulting in either a higher electro-motive force or 
a reduction of the expense for copper in the field coils. 

These cores are called Drum cores when the central hole 
is just large enough for the shaft and the insulation around 
it (Fig. 439) ; and are named Ring cores when the inter- 
nal diameter of the ring is much larger than the shaft. 
(Fig. 441.) The armature in Fig. 442 has a ring core^, but 
the end plates being in position^ the large hole is concealed. 

These cores are built up of a great many punchings of 
soft iron from 15 to 40 mils thick, pickled so as to rust 
them a little. Every tenth one is varnished or tissue paper 




Fig. 441 
simple gramme ring winding 

parted on. The rust, varnish and paper are all insulators 
and when the punchings are assembled in a qotq, prevent 
Eddy currents from flowing from one end of the armature 
to the other and heating it. 

These cores are sometimes smooth, but more frequently 
are slotted with the wires laid in the slots. 

About 10 to 15% of the length of the core is insulation, 
and about 50% of the surface is slotted, containing the in- 
ductors (wires.) 

Continuous Electro-Motive Force. — While a single coil 
of many turns produces a high electro-m.otive force, which 
by a two part commutator is always applied to the exter- 



TJie Dynamo 1047 

nal circuit in the same direction^ yet this coil passes 
through all the changes in voltage mentioned in connec- 
tion with Fig. 426. Fig. 441 shows the construction of the 
Gramme ring^ so named from the inventor, Gramme. The 
winding is on a ring coil made up of soft iron punchings 
25 mils thick. The wires on the outer surface are active, 
having electro-motive force induced in them^ and called ar- 
mature inductors. Fig. 443 shows the same winding with 
eight coils, and eight commutator bars. In Fig. 442 the 
armature as diagramed in Fig. 443 is sliown completed 
with its four bands. These bands are from 12 to 25 con- 




FiG. 442 

EIGHT SECTION EIGHTY COIL RING WINDING ON A SMOOTH RING 
CORE, WITH EIGHTY BAR COMMUTATOR. FOR DIRECT CURRENT 

volutions of phosphor-bronze wire in sizes varying from 
No. 20 up to 14, laid on tightly over a mica insulation and 
sweated with solder all the way round. 

Eeferring to 443 it will be seen that the complete wind- 
ing can be divided into two parts^ one influenced by the N- 
pole^ the other by the S-pole standing at the commutator 
end. The N-pole side moving upwards has its electro-mo- 
tive force in direction from back to front of armature 
through the inductors ; the S-pole side has electro-motive 
force in direction from back to front of armature through 
the dead loire. 



1048 Steam Engineering 

In winding the armature the wire is laid on in a con- 
tinuous spiral as shown. This makes the electro-motive 
force in each half of the armature in series^ and allows the 
current to flow from one coil to another, except at the 
points where the N-half and S-half of the armature meet. 
Here the electro-motive forces oppose and if wires were con- 
nected for an instant to the winding, as shown in the cut. 
the two opposing electro-motive forces would both force 
electricity out into the wire at the top of the armature, and 




Fig. 443 

EIGHT COIL GRAMME RING WINDING, WITH EIGHT PART 
COMMUTATOR 

draw it in at the bottom as shown by the arrows on these 
wires. This will cause a current to flow in the external 
circuit. 

If the junctions of the coils are connected to eight com- 
mutator bars, (one bar per coil); and connect the ends of 
the external circuit by brushes to the commutator bars 
which are midway between the N- and S-poles, then each 
half of the armature separately generates an electro-motive I 
force, and delivers current- to the external circuit. 



The Dynamo 1049 

Suppose the armature to be revolving at the highest safe 
speed. Each inductor will move past the magnet poles at 
a 'speed of 3,000 feet a minute. With pole pieces 5x8 
inches and a flux density of 90,000 lines per square inch, 
the total flux will be 5 x 8 x 90,000 or 3.6 million lines. 

The armature may be 9 inches in diameter which gives 
it rotative speed 1,270 (nearly). 

For E. P. M.*=izP.S.t^(3.1416Xdiameter). 

3000X12 

= =1270 nearly 

3.1416X 9 '^ 

and E.P.S.1:=:21 nearly. 

An inductor therefore cuts 3.6 million lines of mag- 
netism twenty-one times a second, which is equivalent to 
cutting 75.6 millions once per second. 

Since the cutting of 100 million lines per second by an 
inductor induces 1 Volt pressure, each inductor on this 
armature revolving in this field will produce 75.6-^100 or 
% of a volt approximately. 

The 4 coils of 4 inductors each (Pig. 443) on the N-half 
of the armature being in series produce 3 volts per coil or 
a total of 12 volts which is the electro-motive force of the 
generator. 

The S-half of the armature also generates a pressure of 
12 volts, which is not added to the pressure of the N-half, 
i being in parallel with it. An inspection of Fig. 443 sliows 
that they oppose rather than add to each other ; but an out- 
let being provided they turn aside through it, and send cur- 



* Be volutions per minute, 
t Peripheral speed. 
JEevolutions per second. 
§American Wire Gauge. 



1050 



Steam Engineering 



rents separately and independently towards the outside cir- 
cuit. 

If the s^rmature is wound with No. 10 wire A.W.G.§ the 
diameter of which is 0.102 inch or 10.2 mils^ its area is 102 
squared equal to 10^404 c m. Allowing 700 c. m. per am- 
pere, it will carry 15 amperes^ without too much heating. 




A /f 

Two Pole, TwoClrciu; 





Four Pole, Four Circult.Ciuss Connected 
Two Brushes or Four Brushes, 
laMultlDle. 



^ -P 

Four Pole.Two Circuit Rlug 

Two Bruslies or Four Brushes, 

!u Multiple. 



Fig. 444 

SHOWING THE NUMBER AND POSITION OF BRUSHES ON DIFFERENT 
ARMATURE WINDINGS 

The black brushes are the ones actuaHy used, the dotted ones 
being dispensed with on account of the particular winding. 

Since each side of the armature delivers its own current 
to the brushes^ the safe current output of this generator is 
30 amperes. 

Suppose there are 250 ft. of this 'No. 10 wire on this 
armature. The resistance of the wire according to the wir- 
ing table is 1.02 ohms per 1,000 ft. 






■(i;- 



The Dynamo 



1051 



The resistance oi all the tvire on the armature is 0.255 
ohm^ and the resistance of the wire on each half of the ar- 
mature is 0.128 ohm. 

But the two halves are in parallel so the resistance of 
the armature as measured from brush to brush will be one- 



iM 




Fig. 445 



Jialf of 0.128 or 0.064 ohm. The drop, or loss of pressure 
in the armature will be C x E or 30 x 0.064=1.92 or say 2 
\'olts. This machine being a shunt generator, the main 
^nr- current does not pass through the fields, and there is no 
further voltage lost. 



1052 



Steam Engineering 



The electromotive force of this dynamo is 12 volts, and 
its voltage is 10 volts. 

Its output in watts will be 10X30=300 watts or 0.3 
K.W. This is the rating of the machine, and it will carry 




Fig. 446 jO 

this load 22 hours a day without getting more than 90° 
Fahr. hotter than the surrounding atmosphere. A prop-L 
erly proportioned machine will stand a 25 per cent over- ; 
load for half an hour, rising an extra 30° in temperature. , 



The Dynamo 1053 

and it will stand a 50 per cent overload for one minutQ 
without being damaged by the heat. 

Drum Winding, — The extra labor involved in passing 
the dead wire through the bore of a ring core is avoided 
by going back to first principles again, and placing on the 
core, (either drum or ring) a number of coils shaped as in 
Fig. 435, producing a winding as shown in Fig. 439. It 
is to be noted that the inductors lie entirely on the outer 
surface of the core, and that the percentage of dead wire is 
less than in Fig. 441. For a long, small diameter arma- 
ture, drum winding uses the least wire, while for a short, 
large diameter core, the. ring winding will require fewer 
pounds of copper. In order to make the diagram in Fig. 
440 clear it has its proportions wrong. The dead pa^t of 
the wire is drawn very long and the active part very short. 
The reverse is true of an actual winding. 

Keferring to Fig. 439, and using Fig. 440, as a guide, 
the left side of the armature is the N-pole side and the 
right the S-pole side; and the armature is revolving anti- 
clockwise (otherwise the upper brush would be positive). 

The electro-motive forces on the IST-side and S-side of coil 
T, as in Fig. 436, are in series and add up, producing a 
current flow towards the lower (positive) brush. The cur- 
rent passes through the inactive (dead) coil E in order to 
get to the positive brush. 

At the same time the electro-motive forces in coil B add 
up and passing through the dead coil L, drive current out 
of the lower brush. 

The value of the electro-motive force is eight times that 
which one inductor can produce. For the active coil T has 
A loops, i. e., 8 inductors in series, as also has the coil B. 
Suppose T produces 8 volts, the two coils T and B are in 
parallel and do not add their electro-motive forces. 



1054 



Steam Engineering 



The coils L and E are dead, L being in series with B and 
E in series with T^ but they produce no electro-motive force. 
At the present instant they are but a wasteful resistance; 
their value^ however, will be soon seen. 

When the armature has moved about % of a revolutian, 
T is cutting flux slantingly and E, which is in series with 




Fig. 447 



it, is beginning to cut flux also. T is only % active, pro- 
ducing say 6 volts, and E is not totally dead but 14 active^ 
producing 2 volts. Hence the voltage of the machine is 
still 8. 

At 14 revolution E is doing full work and B is dead and 
in series with it, while T is dead and L in series with it is 



Th.e Dynamo 1055 

at full activity. Now E and L produce the electro-motive 
force. 

The current enters the armature through the upper 
brush, splits and passes through the armature by two par- 
allel circuits, one containing T and E in series and the 
other containing L and B. During a revolution these coils 
interchange places, but two coils are always in each circuit. 

When 6 amperes flow in the external circuit the No. 16 
wire of the armature is not overheated, as it has but 3 




Fig. 448 

amperes to carry. It has 2583 circular mils, which is more 
than 3X^00 C. M. .. ; \ ^ ; V ^^ 

Self -excitation of a Dynamo, — When a dynamo is stand- 
ing idle the field magnets are weakly magnetic, due to 
residual magnetism. 

Let the armature revolve, and in a shunt, or compound 
machine open, and in a series generator close the external 
circuit. 

A .few volts will be generated and cause a current to 
flow though the fields, hence the magnetism will increase 



1056 



Steam Engineering 



and more voltage will be induced. This voltage will send 
increased current through the shunt field, and cause more 
volts to be induced. 

The machine is now ^^building up.^^ 

As more and more magnetism is put into the fields, it 
becomes harder to get any more in as the iron is approach- 
ing saturation and there is more and more leakage. 

Hence at a certain point, depending on the design of the 
machine, the difficulty of increasing the magnetism being 




Fig. 449 

added to the eflEect of the leakage just balances the tendency 
of the voltage to be increased. If nothing else is done the 
voltage of the dynamo will remain constant. 

In the series field, is passing all the current drawn from 
the machine, and the field strength and voltage tend to in- 
crease. This increase is opposed by the C. E. loss in arma- 
ture and field, and the effect of the increasing field density. 
The net result is a building up of the voltage and if the 
load is not changed the voltage of the machine will remain 
constant. 



The Dynamo 1057 

Regulation, — If now in the shunt generator the external 
circuit is closed^ an extra current (very large in proportion 
to the field current) is drawn from the armature and causes 
a C.E. loss. 

A lower voltage is thus impressed on the external cir- 
cuity also on the field. Hence the field weakens, and the 
added results of C.E. loss and weaker field is a considerable 
drop in voltage for each increase in load. 

Eesistance must be cut out of the field as load increases. 

When in the series generator the load increases^ a shunt 
should be placed around the field to weaken it, if a con- 
stant potential is desired. 

Position of the Brushes, — -In order that one set of 
brushes may take away from, and the other set deliver cur- 
rent to the generator in a bipolar machine these sets are on 
opposite sides of the commutator. 

In some dynamos when the inductors come out of the 
slots, one goes straight on to a commutator bar, and the 
other is bent over to its proper bar. This puts the brushes 
in line with part of the coil, and they will be found half 
way between the pole tips. 

It is usual to bend both inductors as they leave the slots 

, and connect to bars half way between the slots. Then the 

brushes will be found opposite the middle of the pole piece. 

In dynamos and non-reversing motors the brushes are a 
little distance away from the points mentioned, but in re- 
versing motors are exactly at these points. 

The alternate brushes are of the same polarity, and there 
is usually a set of brushes for each field magnet. 

The placing of the brushes on the commutator with a 
certain relation to the winding is necesary as a reference to 
Fig. 444, or to the diagram of any winding will show that 



1058 Steam Engineering 

the brush while collecting current is at the same time short 
circuiting one of the coils. 

In order that an excessive current may not be generated 
in this short circuited coil it must be out in the interpolar 
space at the time the brush touches the two bars belonging 
to it. 

Brushes and Commulators, — ^Figs. 445 to 449 show dif- 
ferent arrangements of modern brushes and brush-holders. 
These are used to take the current from the commutator 



^' 


\ 




\ 


1 




\ 






\ 


1/ 


B 


WWrr^ 


</f 


Ak 




Fig. 450 



and deliver it to the outside wires in the case of a dynamo, 
and for the opposite in the case of a motor. 

There are many different designs and constructions of 
brushes and brush-holders, and these designs are brought 
about by the various ideas of different builders in their at- 
tempt to produce various advantageous results, but the 
electrical connections and underlying principles. remain the 
same whether a copper or a carbon ^rush be used. 

In any construction of brush holding device, if great care 
is not exercised in keeping it thoroughly clean, trouble is 



Brushes and Commutators 1059 

sure to be the result^ and trouble of this nature increases 
BO rapidly that unless the attendant immediately sets about 
to right it, a burned out armature is aimost sure to be the 
consequence sooner or later. In alternating current dyna- 
rhos, where brushes rest on collector rings instead of com- 
mutators, it is much easier to keep out of trouble, because 
the brushes in this case merely collect the current from the 
rings, and do not commutate or rectify it. 

The brushes and commutator of a dynamo or motor are 
probably the most important parts with which the engineer 

/ 



D 




Fig. 451 



has to deal. Great care should be taken that the brushes set 
squarely on the commutator, and that the surface of the 
brushes and commutator are as smooth as possible. It is a 
good plan, and in some cases the brush-holders are so 
made, that the brushes set in a staggering position, that is 
to say, in a position so that all the brushes will not wear in 
the same place over the circumference of the commutator 
and cause uneven wear across the length of the commutator 
bars. In most machines the armature bearing is arranged 
so that there is more or less side motion, which, when the 



1060 



Steam Engineering 



armatnre is running, causes a constant changing of the po- 
sition of the brushes and commutator. 

Whatever style of brush is used, the commutator should 
be kept clean and allowed to polish or glaze itself while 
running. No oil is necessary unless the brushes cut, and 
then only at the point of cutting. A cloth (not cotton 
waste) slightly greased with vaseline and applied to the 
surface of the commutator while running is best for the 
purpose of preventing the commutator from cutting. 
Should the commutator become rough, it should be 

/ 




Fig. 452 



smoothed with sandpaper, never using emery cloth, because 
emery is a conductor of electricity, and the particles of 
emery are liable to lodge themselves between the commuta- 
tor bars in the mica and short circuit the two bars, thereby 
burning a small hole wherever such a particle of emery has 
lodged itself. The emery will also work into the brushes 
and copper bars and wear them down; it being almost im- 
possible to remove all the emery. 

In the end-on carbon brushes. Pig. 449, the contact sur- 
face of the brushes should be occasionally cleaned by taking 
a strip of sandpaper, with the smooth side of the paper to 



Brushes and Commutator 



1061 



the commutator, and the sanded side toward the contact 
surface of the brush, and then by leaving the tension of the 
brush down on the sandpaper, it is an easy matter to move 
the sandpaper to and fro and thoroughly clean off the 
glazed and dirty surface from the carbon, leaving it with a 
concave *that will exactly fit the commutator. 

The advantages of carbon brushes are many. Among the 
cardinal points are: The armature may run in either di- 
rection without it being necessary to alter the brushes ; the 
carbon can be manufactured with a quantiy of graphite in 
its construction, thereby lowering the mechanical friction 



r^ /^«t-« ' 



WR 



AAAAA^-Q 




Fig. 453 



of the brushes on the commutator ; they do not cut a com- 
mutator so much by sparking ; the commutator has a longer 
life, the wear being more evenly distributed. 

Carbon brushes, due to their rather high resistance, will 
often heat up considerably, but, although this heat is ob- 
jectionable, their resistance tends to cut down the sparking. 
The brushes are sometimes coated with copper to reduce 
their resistance. Often a carbon brush will be found which 
is very hard. As a rule such a brush should be thrown 
away, as it will heat abnormally and at the same time wear 
the commutator. 



1062 Steam Engineering 

In Fig. 450 we have one of the various so-called old 
styles of leaf brush-holders. The end-on brushes are more 
generally used in modern practice^ because their contact 
surface area is not increased or decreased by wear. Conse- 
quently the brushes always remain in a diametrically oppo- 
site position. With the old style brush-holding device^ 
where the brushes rest on the commutator at a tangent^ 
great care should be exercised not to allow the brushes to 
wear in a position so that their points will be out of dia- 
metrical opposition. Fig. 450 shows the correct setting ox 




Fig. 454 

this type of brushy and Figs. 451 and 452 show the incor- 
rect setting. 

By remembering that each one of the commutator bars 
is the end of a coil, and then just mentally tracing the cur- 
rent through the coils from one brush to the other, we can 
readily understand what the results are when the brushes 
are neglected and left in a relative position, as shown in 
these figures. 

Sparking is the usual result of brushes allowed to wear 
to such an extent. Overloading of a dynamo or motor will 
also cause serious sparking, and no amount of care can 



Brushes and Commutator 1063 

prevent damage to armature, commutator or brushes, if a 
machine is permitted to be overloaded. 

Sometimes the commutator will contain one or more 
bars which, as the com^mutator gets old and wears down, 
will wear away either too fast or too slow, due to the metal 
being harder or softer than the rest of the bars forming 
the commutator. This causes a roughness of the commu- 
tator, and results in the flashing of the brushes and heating 
of both the commutator and brushes. About the only sat- 
isfactory method of remedying this evil is to take out the 
armature, and have the commutator turned down in a lathe. 

A short-circuited coil in the armature, or a broken arma- 
ture connection, will also cause considerable sparking. 
Either of these conditions can be located by means of a 
Wheatsone bridge, or by what is known as the fall of po- 
tential method. To make a test with this latter method, 
connect in series with the armature to be tested some re- 
sistance capable of carrying the necessary current, also an 
ammeter. Some apparatus for varying the current strength, 
such as a water rheostat, or lamp rack, must be connected 
in the circuit, a diagram of which is shown in Fig. 453. 

In the diagram, WR is the water rheostat or lamp rack, 
E the known resistance, A the ammeter and M the arma- 
ture to be tested. By means of the water rheostat regulate 
the current passing over the apparatus until it is of such 
stj-ength that a deflection can be obtained on a voltmeter 
when it is connected to two adjacent bars on the commuta- 
tor. Suppose the armature coil between bars 1 and 2 on 
the commutator were broken. The voltmeter connected 
across these two bars would give the same reading as when 
connected across the two points 10 and 11. If the volt- 
meter were connected between any other two points on the 
commutator on the same side as the broken coil no deflec- 



1064 Steam Engineering 

tion would be obtained, while connecting the voltmeter be- 
tween any two adjacent bars on the other side of the com- 
mutator would give practically the same reading irrespect- 
ive of which bars were used. The resistance of one or more 
sections of the arm.ature winding could also be found by 
using Ohm^s law, R=E/C, or the resistance would be equal 
to the voltage divided by the current as shown on the am- 
meter. It must be remembered that this latter will be true 
only when there is an open coil in one side of the armature, 
for in this case only will the whole current flow through the 
one side. If the coil between bars 1 and 2 were short cir- 




FiG. 455 

cuited, the voltmeter would show practically no reading 
between these bars ; while between any other bars some de- 
flection would be obtained. An open circuit, or short cir- 
cuit will nearly always be found by examination, as the 
trouble usually happens very close to the commutator con- 
nections in the case of an open circuit, and may very often 
be found between the commutator bars themselves, in the 
case of a short circuit. If the trouble is not at these places 
it will usually be in the windings, in which case the only 
remedy is to have it re-wound. Temporary repairs may be 
made in the case of an open circuit by short circuiting the 



Brushes and Commutator 



106E 



commutator bars around the open circuity but this method 
should only be used in emergency^ as the sparking will in 
time destroy the commutator. 

With many dynamos, especially of older types, it is nec- 
essary to shift the brushes with every change of load. The 
current produced by the armature makes a magnet out of 
it, and the magnetism of the armature opposes that of the 
fields. In Fig. 454 the armature is working with a very 
light load and the lines of force of the field magnets are 



I -posi 



i^ivc 




Fig. 456 
showing position of brush for sparklers. 

CURRENT 



COLLECTION OF 



only slightly opposed by those of the armature. In Fig. 
455 we assume a heavy load on the dynamo and conse- 
quently the magnetism of the armature opposes that of the 
fields. This changes the location of the neutral point 
(when the coils under the brush generate no current) and 
it becomes necessary to shift the brushes accordingly, or 
great sparking would result The amount of shifting nec- 
essary with changes of load varies in different dynamos. 
If the field is very strong compared to the armature, it will 
be but little. If the armature (as in some arc dynamos) 



1066 



Steam Engineering 



is very strong compared to the field, it \^ill be considerable. 

In dynamos, with increasing load, the brushes should 
be shifted in the direction of rotation, and in the opposite 
direction when the load decreases. 

Never allow a dynamo or motor to stand in a damp place 
uncovered. Moisture is apt to soak into the windings and 
cause a short circuit or ground when started. Great care 
should also be used should it ever be found necessary to use 
water on a heated bearing. If the water is allowed to reach 




Fig. 457 
circuits in a series dynamo or motor 



the armature, or commutator, it is bound to cause trouble. 
Water should only be used in case of emergency, and then 
sparingly. 

Sparking. — "V^Tien a current is broken there is always a 
spark, which is greater the more turns in the wire, and the 
more iron within these turns. That is, the more inductive 
the current the worse the spark. 

The conditions are right for excessive sparking in a ma- 
chine, for the circuit is inductive and, although the circuit 



Brushes and Commutator 1067 

is not actually broken, the current being merely shifted, 
yet the result is equivalent to it. 

Looking at Fig. 456 and considering the line N N" to be 
about midway between the pole pieces. The coil B is short 
circuited but has no currei^t in it because: 

1. The field is very weak and the coil is moving paral- 
lel to it, so no electro-motive force is generated in the coil. 

2. The currents from the N- and S-side of winding en- 
ter the brush without going through the coil B. 

Coil B has therefore no current in it, but being connected 
to A and C whose potential is high, B is charged with elec- 
tricity, and it is full of coulombs,^ which, are at rest. 

When the armature revolves as shown and the toe of a 
copper brush leaves bar 3 the current from C must instantly 
change over going through B to reach the brush. The 
coulombs in B which are at rest should instantly move at 
full speed becoming a part of the armature current. 

It being impossible to set the coulombs in B into motion 
instantaneously, it is evident that the current from C en- 
counters more than the ohmic resistance of the coil B. This 
extra opposition is called reactance. 

The path through B being momentarily practically non- 
conducting, the circuit is broken by the bar moving away 
from the brush, and a spark or arc formed. 

The circuit being inductive (having turns containing 
iron), the spark is persistent and holds until the reactance 
of coil B decreasing, it begins to conduct and diverts 
enough current into the proper path, and the arc goes out 
for lack of current to maintain it. 



*A coulomb is a certain quantity of electricity. When 
a coulomb passes a given point every second a current of 
one ampere is said to flow. 



1068 Steam Engineering 

This sparking is avoided in the following way: 

1. Carbon brushes of high resistance are used which, 
as the part of the brush touching a bar gets narrower, due 
to the high resistance, throttle the current, gradually forc- 
ing it over to the coil B. Hence B does not have to in- 
stantly carry all the current. 

2. Move the brushes of a dynamo in direction of rota- 
tion until they are nearer the pole shoe, exactly as is shown 
in Pig. 456. 

The short cicuited coil B is now under the fringe from 
the pole piece ; and is moving obliquely through a stronger 
field. A small electro-motive force is generated in it. 

From the illustration it will be seen that a current in the 
same, as in G (for B and C are under influence of same 
pole piece) flows around through B, the bars 2 and 3 and 
the brush. 

By shifting the brushes a little to and fro the correct 
strength of field can be selected, and the obliquity at which 
it is cut adjusted, so that a current will be made to flow 
in B not only of the same direction as that in C, but also 
of exactly the same value. 

Hence when the toe of the brush slips from bar 3 the 
current in C instead of running against the impedance 
(the sum of the resistance and reactance) of coil B, finds 
itself merely falling in behind the flow already established, 
and there is no tendency to spark. 

In a motor the brushes are shifted in opposite direction 
to the rotation to get the no sparking position. Hence the 
positions for sparkless forward or backward running are 
some distance apart. ' 

It is a mere matter of first cost to produce a machine 
with absolutely sparJcless commutation under any condi- 
tions. It is the skill of the designers which has (without 



Types of Dynamos 



1069 



prohibitive cost) so reduced the distance between these two 
points that it may be spanned by a thick carbon brush. 



TYPES OF DYNAMOS. 

Dynamos are divided into different types with reference 
to the manner in which their fields and armature are inter- 
connected. 

Ammeter 



Resistance Box 




~affi 



Fig. 458 
circuits of a shunt dynamo with instruments and a load of 

LAMPS 

The series dynamo, — Pig. 457. The same current tra- 
verses the fields armature and main or external circuits. 
The conductors in these circuits are about the same size. 
The circuits are all in series. 

This dynamo is used for arc lighting and, as a booster 
for increasing the pressure on a feeder carrying current 
furnished by some other generator. 

The characteristic of this type is to furnish power at an 
increased voltage as the load increases. If sufiicient current 
is drawn to overload the machine, the voltage will drop. 



1070 Steam Engineering 

The shunt dynamo. — Fig. 458. Here the field circuit is 
arranged as a shunt circuit. The armature and external 
circuits are in series. The armature current is the sum of 
the external^ and field currents. The conductors on the 
field are very much smaller than those on the armature, as 
they carry only 2 to 5 per cent as much current! The shunt 
dynamo is used for incandescent lamp lighting, and mill 
and factory power. 

The leading characteristic of the shunt generator is ta 
allow the voltage to fall, as the load is increased. It is 
evident that only by a combination of these two classes into 
a compound dynamo, Fig. 459, can a generator be pro- 
duced which will deliver any power within its rated capac- 
ity, and still hold a steady voltage. 

The armature is similar to the armature of the shunt dy- 
namo, but the fields have two distinct windings, one shunt 
and the other series. 

The series dynamo is often called a constant current 
generator because its tendency is that way, and with a reg- 
ulator it will furnish a constant current. 

The shunt dynamo is similarly termed a constant poten- 
tial generator. For with a regulator it will keep to a con- 
stant voltage. 

If a compound wound dynamo is supplying a circuit at 
a constant potential it may be almost self regulating. Sup- 
pose that the resistance of the external circuit be dimin- 
ished. This will send more current through the series coil, 
thus increasing the intensity of the field. But the reduc- 
tion of the resistance in the outer circuit reduces the cur- 
rent in the shunt winding. This action tends to reduce the 
intensity of the field. 

If the two exciting coils, viz. shunt and series, are prop- 
erly proportioned, the intensity of the field may be main- 



Types of Dynamos 



1071 



tained practically constant^ even though the resistance of 
the external circuit is increased or diminished. The arma- 
ture being kept at a constant speed of rotation^ in a con- 
stant field of f orce^ by the engine^ or other source of power, 
it will impress upon the circuit a constant voltage. This 
applies of course to an accurately arranged winding. 

Over compounding. — The result of such even action is 
the maintenance of a constant voltage at the terminals of 
t}]e machine. In electrical work^ all sorts of conditions 
must be met. A verv usual one is that on a circuit a con- 




FiG. 459 

CIRCUITS IN A COMPOUND DYNAMO 

stant voltage is required, not at the generating plant, but 
in the heart of the district several miles distant. In an 
over-compounded dynamo the series coil is given a certain 
number of turns in proportion to the turns in the high 
resistance shunt coil, and the influence of the series coil 
overbalances that of the shunt coil. The result of over- 
compounding is to cause the voltage at the terminals of the 
machine to rise with the increase of current. The propor- 
tional increase of voltage with increase of current can be 
accurately regulated by the relative sizes of the coils. It is 
only necessary to follow what has been said regarding the 



1072 Steam Engineering 

series dynamo, and to regard the compound wound ma- 
chine as a series dynamo greatly reduced in its character- 
istic action. Over-compounding makes it possible to main- 
tain a constant voltage at any point within a district. The 
resistance of the mains between the dynamo in the central 
station, and the given point in the district is known. The 
drop in voltage due to that resistance varies with the cur- 
rent. The over-c'ompounding of the machine can be reg- 
ulated to give the same increase in voltage with the in- 
crease in current, and thus the voltage at any desired point | 
in the district can be kept constant, following Ohm^s law. 
Suppose that the resistance of a single lead of the mains is 
0.01 ohm. Then the resistance of the two leads is 0.02 ohm. 
Assuming a maximum current of 500 amperes is needed, 
the drop due to the specified resistance and current will be 
1{I=E, or 0.02X500=10 volts. This is an extreme case, 
but the dynamo by over-compounding can be made to vary 
its voltage at the terminals in this, or in any other desired 
proportion to the current. With the resistance given above, 
and the variation in voltage for the current as calculated 
above, which variation is at the terminals, a constant volt- 
age would be maintained at the outer portion of the leads. 
The series field coils of a dynamo can only be excited by 
the working current, or by a portion of it. When the ma- 
chine is compound wound, the series coils are taken care of 
by the machine, but the shunt coils may receive their cur- 
rent from other sources. But in order to make the dynamo 
self regulating, the shunt coil should be fed from the ma- 
chine proper. This practice also makes the dynamo self- 
contained. In some cases the terminals of the shunt coils 
are connected to the leads, or bus bars of the main circuit, 
and if several dynamos are operated, and a constant poten- 
tial maintained in the circuit at all times, a new element is 



Types of Dynamos 



l<i17& 



introduced in the excitation of the field, for the reason that 
the current in the shunt coil is independent of the speed 
of the dynamo, and the shunt coils continue to excite the 
field to a certain extent, and this excitation is never re- 
duced to zero until the connection with the bus bar, or main 
connection is broken. This is a case of under-compound- 
ing, and the advantage of it is that it makes it possible to 
excite the field before starting the dynamo. The field is 
not only excited, but the correct polarity is established be- 




FiG. 460 

SEPARATE-CIRCUIT DYNAMO 

fore the armature begins to revolve. The capacity of the 
shunt coil is considerable, and it cannot with safety be dis- 
connected by a simple opening of a switch. A bank of 
lamps is generally mounted in series with it, and the field 
break switch is placed between the lamps and the main cir- 
cuit. When it is opened the resistance of the lamps pre- 
vents undue sparking. The shunt coil may also be excited 
by an entirely independent source of electric energy, as a 
storage battery, or an exciting dynamo. The exciting ma- 



lO^i 



steam Engineering 



chine may be run at a constant voltage^ thus passing an 
absolutely constant current through the excited shunt coils. 
The separately excited dynamo resembles the magneto 
in its action^ as the field strength does not directly depend 
upon the current generated. The separate circuit dynamo 
has either two separate armatures in the field space, or it 
may have two sets of coils. Whichever it is, one armature 
or coil set is used to excite the field, and the other to sup- 
ply the current to the circuit. Fig. 460 shows such a dyna- 
mo with two commutators, one for supplying the main cir- 
cuit, and the other the field magnet current. 

OPERATION or DYNAMOS. 

Constant Potential Dynamos. — In order to thoroughly 
explain the operation of dynamos, let us assume that we 




Fig. 461 



have the task of starting a new shunt dynamo, one that 
has never generated any current. Our first step is to open s 



Operation of Dynamos 



1075 



the main switch and turn the rheostat or field resistance 
box so that all the resistance is in circuit. A rheostat con- 
sists of a number of resistances, Figs. 461 and 462, so ar- 
ranged that they can be cut in or out of the circuit with- 
out opening the circuit. By reference to Fig. 462, it will 
be seen that the current enters at the handle, and from 
there passes to the contact point upon which the handle 
happens to rest. If the handle is at 1 the current must 
pass through all the wire in the box; if it is at 2 it simply 
passes through the handle and out. 




Fig. 462 

Eheostats for the shunt circuit of a dynamo should have 
iSufficient resistance, so that when it is all inserted, the 
ivoltage of the dynamo will slowly sink to zero. This 
method of stopping the action of a dynamo is perfectly 
safe, and should be followed wherever possible. 

We are now running our dynamo with all resistance in 
the shunt circuit. This is simply as an extra precaution 
because we know nothing about this particular dynamo. 
When it is known that the dynamo is in good order, the 



1076 



Steam Engineering 



engineer or attendant "asually cuts out all the resistance, 
and as the generator builds up or, in other words, generates 
current, he proceeds, by the aid of the resistance box, to cut 
down or diminish the flow of electricity around the field 
magnets of the dynamo, and thereby diminish the mag- 
netic density of the field magnets, and the electro-motive 
force of the dynamo. 




(ttrrnrf) 



Fig. 463 



We must now gradually turn our rheostat so as to cut 
out resistance, and watch the voltmeter, which is connected 
as shown at V in Fig. 463, and receives current whenever 
the dynamo is operating. Suppose that the voltmeter in- 
dicates nothing, and we find that the dynamo will not gen- 



Operation of Dynamos 1077 

erate. On examination of all the connections we find every- 
thing correct, and we now discover that the dynamo field 
magnets do not contain what is termed ^^residual magne- 
tism^^ sufiicient to start the process of generating current. 

Before an armature can generate current it must cut 
lines of force, that is, is must revolve in a magnetic field. 
If the dynamo has been generating current it is likely that 
the iron cores of the field magnets will retain sufficient 
magnetism to start the generation of current again. This 
magnetism which remains in the iron is known as residual 
magnetism. It will make itself manifest by attracting the 
needle of a compass, or if strong, a screw driver or a pair 
of pliers. If we find no magnetism in the iron core of the 
field magnets, we may take the ends of the shunt winding 
on the field magnets and pass current over them from a 
battery. This current will produce sufficient magnetism 
to cause the generator to build up; in other words, if we 
disconnect these batteries, and connect the wires back again 
from where we got them, we will find that we can generate 
current with the machine. 

When the machine begins to generate, we watch the volt- 
meter, and cut resistance in or out of the circuit according 
whether we need to lower or raise the voltage. If we have 
only one dynamo we may close the main switch before we 
begin generating, or after we have attained full voltage. 

Again referring to the pole pieces on the dynamo, it is 
possible that there is a sufficient quantity of residual mag- 
netism in the pole pieces, and that the polarity of both 
field magnets, between which the armature is revolving, is 
the same. This would also cause the dynamo to fail in 
generating current. If sending battery current through the 
coils does not make one field a north pole and the other a 



1078 Steam Engineering 

south pole, one of the fields must be connected wrong and 
we must make some changes in the connection. 

Eef erring to Fig. 463, a and & are the terminals of the 
shunt winding on the fields. If the winding of the fields 
is correctly put on it will be as in the little sketch at lower 
corner ; that is, if both field magnets were taken out of their 
places and put together, the winding should run as one 
continuous spool. But if the winding on one field is wrong, 
we need simply change its connection, as, for instance, 
transferring c to a and a to c. 

In order that a dj^namo may excite itself, it is necessary 
that the current produced by the residual magnetism shall 
flow in such a direction as to strengthen this residual mag- 
netism. If the current poduced by the residual magnetism 
flows through the field coils in the opposite direction, it 
will tend to weaken the residual magnetism, and conse- 
quently to reduce the current which flows. 

For this reason if the first attempt to start a dynamo 
with battery current fails, the battery should be applied 
with the opposite poles so that the magnetism it produces 
in the fields will be in the opposite direction. 

The magnetism, the fields, and all parts of the dA^namo 
may be in perfect working order, and yet a short circuit in 
any part of the wiring will prevent the dynamo from build- 
ing up. This short circuit will furnish a path of such low 
resistance that all current will flow through it and none 
can flow through the flelds to induce magnetism. Often 
dynamos fail to generate because of broken wires in the 
field coils, poor contacts at brushes, or loose connections. 
Sometimes also part of the wiring may be grounded on the 
metal parts of the dynamo frame. A faulty position of 
the brushes may also be a cause for the machine not gen- 
erating. In some machines the proper position for the 



Operation of Dynamos 



ia79 



brushes is opposite the space between the pole pieces, while 
in other machines their proper position is about opposite 
the middle of the pole piece. If the exact position is not 
known^ a movement of the brushes will sometimes cause 
the generator to build up. 

If there are several dynamos to be started great care 
must be taken to see that the second m.achine is operating 
at full voltage before the switch is closed connecting it to 




Fig, 464 



the switch board. The voltage should be exactly the same 
as that of the first machine and the rheostat worked to keep 
it so. If it is less^ it is possible that the first machine will 
run the second as a motor; if it is more, the second ma- 
chine may run the first as motor, the machine having the 
higher voltage will always supply the most current. 

It is also necessary before throwing in the second. ma- 
chine (connecting it to the switch board) to see that its 
polarity is the same as that of the machine with which it 



5080 Steam Engineering 

is to be run. By reference to Pig. 464 it will be seen that 
the + poles of both machines connect to the same bar, and 
if one of these machines is running and we wish to connect 
the other with it, we must first be sure that the wire of the 
second machine which leads to the top bus-bar is of the 
same polarity. That is, if the top bus-bar is positive, or 
sends out current, the wire of all dynamos connected to it 
must also be positive. The simplest way to find the posi- 
tive pole of a dynamo, is with a cup of water. Take two 
small wires and connect one to each of the main wires of 
the dynamo and then insert the bare ends of both wires 
into the water, small bubbles will soon be seen to rise in 
the water from one of the wires. That wire which gives 
off the bubbles is the negative wire. Take care that in 
making this test you do not get the ends of the small wires 
together or against the metal of the cup or you will form 
a short circuit. The polarity of both dynamos must be 
tested and wires of same polarity connected to the same 
bus-bar. 

Where several machines are to be operated in parallel, 
compound dynamos are generally used, because it is 
troublesome to keep two shunt machines working in har- 
mony. 

The starting of a compound wound dynamo is the same 
as that of a plain shunt dynamo, but in connecting a com- 
pound wound dynamo to its circuit it is necessary to be 
sure that the shunt coils and series coils tend to drive the 
lines of force around the magnetic circuit in the same di- 
rection. If the series coil is connected up in the opposite 
direction to the shunt coil the dynamo will build up all 
right, and will work satisfactorily on very light loads. 
When, however, the load becomes even, five or ten per cent, 
of full load, the voltage draps off very rapidly, and it is im- 



Operation of Dynamos 1081 

possible to get full voltage with even half the load on. This 
is because the ampere turns due to the series coils decrease 
the total ampere turns acting on the magnetic circuit in- 
stead of increasing them as the load comes on. This lowers 
the magnetic flux and of course lowers the resulting volt- 
'age. In such a case it will be necesary to reverse either the 
field or series coils. 

Pig. 464 shows connections for two compound wound 
dynamos run in parallel. When two or more compound 
wound dynamos are to be run together^ the series fields of 
all the machines are connected together in parallel by 
means of wire leads or bus-bars which connect together the 
brushes from which the series fields are taken. This is 
known as the equalizer^ and is shown by the line running 
to the middle pole of the dynamo switch. By tracing out 
the series circuits it will be seen that the current from the 
upper brush of either dynamo has two paths to its bus-bar. 
One of these leads through its own fields^ and the other, by 
means of the equalizer bar^ through the fields of the other 
dynamo. So long as both machines are generating equally 
there is no difference of potential between the brushes of 
No. 1 and No. 2. Should, from any cause, the voltage of 
one machine be lowered, current from the other machine 
would begin to flow through its fields and thereby raise the 
voltage, at the same time reducing its own until both are 
again equal. The equalizer may never be called upon to 
carry much current, but to have the machines regulate 
closely it should be of very low resistance. It may also be 
run as shown by the dot^ted lines but this will leave all 
the machines alive when any one is generating. The am- 
meters should be connected as shown. If they were on the 
other side they would come under the influence of the 
equalizing current and would indicate wrong, either too 



1082 Steam Engineering 

high or too low. The equalizer should be closed at the 
same time^ or preferably a little before the mains are closed. 
In some cases the middle^ or equalizer^ blade of the dyna- 
mo switch is made longer than the outside to accomplish 
this. 

The series fields are often regulated by a shunt of va- 
riable resistance. 

To insure the best results compound machines should 
be run at just the proper speedy otherwise the proportions 
between the shunt and series coils are disturbed. 

GENEKAL RULES. 

1. Be sure that the speed of the dynamo is right. 

2. Be sure that all the belts are sufficiently tight. 

3. Be sure that all connections are firm and make good 
contact. 

4. Keep every part of the machine and dynamo room 
scrupulously clean. 

5. Keep all the insulations free from metal dust or 
gritty substances. 

6. Do not allow the insulation of the circuit to become 
impaired in any way. 

7. Keep all bearings of the machine well oiled. 

8. Keep the brushes properly set^ and see to it that they 
do not cut^ or scratch the commutator. 

9. If the brushes sparky locate the trouble and rectify 
it at once. * 

10. The durability of the commutator and brushes de- 
pends on the care exercised by the person in charge of the 
dvnamos. 



Operation of Dynamos 1083 

11. At intervals the dynamos must be disconnected 
from the circuit and thoroughly tested for leakage and 
grounds. 

12. In stations running less than twenty-four hours 
per day^ the circuit should be thoroughly tested and 
grounds removed (if any are found) before current is 
turned on. 

13. Before throwing dynamos in circuit with others 
running in multiple, be sure the pressure is the same as 
that of the circuit; then close the switch. 

14. Be sure each dynamo in circuit is so regulated as 
to have its full share of load, and keep it so by use of re- 
sistance box. 

15. Keep belting in good order; when several machines 
are operating in parallel and a belt runs off from one, the 
others will run this machine as a motor. 

16. In the same way if you shut down an engine driv- 
ing a generator, the other generators will run the genera- 
tor and the engine. 

Constant Potential Switchboard. — Fig. 465 illustrates 
the usual type of switchboard employed to connect, or 
switch various dynamos, and to feed various circuits from. 
These types, sizes and arrangements of switchboards vary, 
and depend entirely on the type and size of the plant, the 
number of dynamos used and the number of circuits to be 
controlled. The switchboard in this cut has three dynamo 
panels, and one load panel. At the left of the board and 
near the top is the voltmeter, while on the three left panels 
are the dynamo main switches and their respective amme- 
ters. On the lower part of these three machine panels will 
be noticed the protruding hand wheels of the field resist- 
ance boxes, which are hidden back of the board. The meter 



1084 



Steam Engineering 



at the top of the right hand panel is the load ammeter and 
registers the total number of amperes that are being sup- 
plied to the circuits whose several switches are just below 
the meter. 




Fig. 465 



Fig. 466 shows diagrammatieally the reverse side of a 
similar switchboard. Below all of the switches there are 
installed fuses in each wire. The object of these fuses is 
to protect the wires and also the dynamos. These fuses 
consist of an alloy which melts at a comparatively low 
temperature. If^ for instance^ a short circuit occurs in 



Operation of Dynamos 



1085 



any line^ the current will suddenly become very strong and 
will generate considerable heat. This heat will cause the 
fuse to melt and open the circuit. If the fuse did not 
melt^ the current would continue and overheat the wires, 
causing considerable damage and perhaps fires. The fuses 




6 o 0, 



^ 6 



6 6 6 
+ 9 o 9 



6 6 6| 
+ 9 9 9 



Ml.. ... 

^■' 6 6 6 6 6 6 6 

?8 n n u 



IS 2+ iS 2+ 



U 1 U i 

Sujitches 

^ 9^ y ? ^ 



Fig. 466 

should always be chosen of such a size that they will melt 
before the current rises enough to do any damage. 

Operation of Constant Current Dynamos, — Constant cur- 
rent dynamos differ from^ constant potential dynamos 
mainly in the higher voltage for which they are usually 
constructed. Such machines are always more or less dan- 



1086 Steam Engineering 

geroTis to life, and great care must be taken not to touch 
any of the current-carrying parts with bare hands. 

AVhen such parts must be handled, rubber gloves are 
very convenient and useful if kept dry. High voltage 
machines should always be surrounded by insulating plat- 
forms of dry wood, or rubber mats, so arranged that one 
must stand on them in order to touch any part of the 
^machine. By reference to Fig. 467 it will be seen that 
the constant current dynamo is not equipped either with 
a voltmeter or a field rheostat; but an ammeter should 
always be used. The troubles encountered with these dy- 
namos are much the same as those of constant potential 
dynamos. Most of them are referred to in the following 
descriptions and instructions for different systems and to 
avoid repetition need not be mentioned here. 

The type of dynamo generally used with constant cur- 
rents is shown in Fig. 467 and is series wound; that is, 
the same current that passes through the lights and outer 
circuit also passes through the fields and excites them. 
The fields of this dynamo are connected with a short cir- 
cuiting switch S, which is generally used when the ma- 
chine is to be shut down. When this switch is closed it 
forms a path of much lower resistance than do the fields 
of the dynamo, and all current passing through it and the 
dynamo loses its magnetism and stops generating. A 
constant potential dynamo will not begin generating if 
there is a short circuit anjr^here in the wiring connected 
with it, but with the constant current dynamo it is often 
necessary to provide a short circuit in order to start it. 
If there is very much resistance in the line, or if it is 
entirely open the dynamo will fail to generate. 

In order to start generation a small wire may be at- 
tached to one of the terminals of the dynamo and the 



Operation of Dynamos 



1087 



other end brought in contact with the other terminal for 
a fraction of a second or the shortest possible instant. If 
the circuit happens to be arranged somewhat as shown in 
Fig. 467^ the plug may be inserted so that the dynamo 
is started through only one lamp. When this lamp is 
burning properly the plugs may be suddenly withdrawn 




Fig. 467 



and the current will now force itself through the other 
lamps. This process is known as "jumping in'^ and should 
be used only in an emergency, as much damage may be 
caused, especially if a dynamo is already running a large 
number of lamps and is then "jumped into^^ a bad circuit. 
This is also often done, but is just as dangerous as it would 



1088 Steam Engineering 

be to attempt to start a heavy steam engine by opening 
up the throttle valve with a quick jerk. 

Constant current dynamos are^ or should be always equip- 
ped with automatic regulators^ and before the dynamo is 
started special attention must be given the regulator to 
see that it is in proper working order. 

Often it may be desirable and even necessary to run two 
dynamos in series, as, for instance, if a circuit has been 
extended beyond the capacity of one machine. In such 
a case the regulator of one machine is cut out, and that 




Fig. 468 



machine set to operate at about its highest electromotive 
force, and the variations are taken care of by the other 
dynamo. 

The Brush System, — The brush arc dynamo is quite dis- 
tinct from other constant current dynamos in general use. 
The brush arc generator is of the open coil type, the funda- 
. mental principle of which is illustrated in Pig. 468. Two 
pairs of coils, placed at right angles on an iron core, are 
rotated in a magnetic field. The horizontal coils repre- 
sented in the diagram are producing their maximum elec- 
tromotive force, while the" pair of coils at right angles to 



Operation of Dynamos 



1089 



them is generating practically no electromotive force. The 
brushes are placed on the segments of the four-part com- 
mutator^ so as to collect only the current generated by the 
two horizontal coils. The other coils are open circuited or 
completely cut out of the circuit. 

Such a machine will generate current^ continuous in di- 
rection^ but fluctuating considerably in amount. These 







Fig. 469 



fluctuations will be diminished by the addition of more 
coils to the armature. 

Fig. 469 shows the connections of an eight-coil brush 
arc generator. Each bobbin is connected in series with 
the one diametrically opposite. The connection is not 
shown on the diagram. It will be noticed that of those 
coils connected to the outer ring on which the brushes A 



1090 Steam Engineering 

and A^ bear^ only 3^ 3^ are in circuit, 1, 1^ being entirely 
cut out; while on the inside ring all coils 2, 2^ and 4, 4^ 
are in circuit, the two pairs being parallel ; 4, 4^ are com- 
ing into the field of best action; in other words, they are 
approaching that part of the field in which there is most 
rapid change of magnetic flux, while 2, 2^ are approaching 
that part in which the flux is uniform. In 4, 4^ there is 
an increasing electro-motive force being generated, and 
the current is rising; while in 2, 2^, the electromotive force 
is decreasing and the current falling. Unless 2, 2^ were cut 
out of the circuit a point would soon be reached where the 




Fig. 470 

electromotive force in 2, 2^ would be zero, and consequently 
4, 4^ would be short circuited through 2, 2^. Just before 
this occurs, however, 2, 2^ have passed from under the 
brush, and the small current still flowing draws out the 
spark seen on the commutator of all open coil machines. 
Setting the Brushes. — A pressure brush should always 
be used over the under brush in the same holder, ^as it 
improves the running of the commutator and secures 
better contact on the segment. The combination is re- 
ferred to as the ^^brush.^^ The brushes should be set 
about 5% in. from the front side of the brass brush- 
holder. 



Operation of Dynamos 1091 

In setting the brushes^ commence with the inner pair 
and set one brush about 5% in. from the holder to tip of 
the brushy then rotate the rocl^er or armature until the 
tip of the brush is exactly in line with the end of a copper 
segment^ as shown in Fig. 470. The other brush should 
be set on the corresponding segment 90° removed (the 
same relative position on the next forward segment) ; but 
if the length of the brush from the holder is less than S^/s 
in., move both brushes forward until the length of the 
shorter brush from the holder is 5^/8 in. Now set the two 
extreme outer brushes in the same manner^ clamping 
firmly in position, and by using a straight edge or steel 
rule, all the brushes can be set in exactly the same line 



1 I 

Fig. 471 Fig. 472 Fig. 473 

and firmly secured. The spark on one of the six brushes 
may be a trifle longer than on the others. In this case, move 
the brush forward a trifle so as to make the sparks on the 
six brushes about the same length. Equality in the spark 
lengths is not essential, but it gives at a glance an in- 
dication of the running condition of the machine. 

Brushes should not bear on the commutator less than 
% in. from the point of the brush, or, as illustrated in 
Fig. 471, they will tend to drop into the commutator 
slots and pound the copper tip of the wood block, causing 
the fingers of the brushes to break off. If, on the other 
hand, the bearing is too far from the end, or the brushes 
are set too long, as in Fig. 472, the point of the brush will 
not be in contact with the segment, thereby prolonging 



1092 Steam Engineering 

the breaks and allowing the spark to follow the tip with 
consequent burning of the segments and brushes. 

Fig. 473 shows correct setting with the tip of the brush 
nearly tangential and stiff on the segment as it leaves. 

Care of Commutator, — If the commutator needs lubri- 
cation, oil it very sparingly. Once or twice during a run 
is ample. If the oil has a tendency to blacken the com- 
mutator instead of making it bright, wipe the commutator 
with a dry cloth. Too much oil causes flashing. 

The machine, of course, generates high potential, and 
the cloth, or whatever is used to oil the commutator, 
should therefore be placed on a stick so that the hand is not 
in any way between the brushes. 

A rubber mat should be provided for the attendant to 
stand on when working around the commutator or brushes. 

One hand only should be used, and great care 'exercised 
not to touch two brush clamps or brushes at the same 
time; never with switches closed. 

As soon as current is shut off from the machine the com- 
mutator should be cleaned. A piece of very fine sandpaper 
held against the commutator under a strip of wood for 
about a minute before the machine is stopped, will scour 
the commutator sufficiently. The brushes need not be re- 
moved. An effort should be made to have the machine 
cleaned immediately after it is shut down. Five minutes 
at that time will give better results than half an hour when 
the machine is cold. K'ever use a file, emery cloth or cro- 
cus, on the commutator. New blocks will sometimes cause 
flashing, due to the presence of sap in the wood. The ma- 
chine should be run for a few hours with a slightly longer 
spark, say % in., and the commutator then thoroughly 
cleaned with fine sandpaper. 



Operation of Dynamos 



1093 



All constant current arc machines require an auto- 
matic regulator to increase the voltage as more lamps are 
cut into the circuit, and decrease it as lamps are cat out. 




To Controller 



Fig. 474 



\ To Control /er 



We will give only one of the several forms of regulators 
used with this system. 

The form 1 regulator is placed on the frame of the 
machine beneath the commutator, and a constant motion is 
imparted to its main shaft through a small belt running 



1094 



Steam Engineering 



around the armature shaft. (See Fig. 474.) By means 
of magnetic clutches and bevel gears^ a pinion shaft is 
rotated, which moves the rack and the rocker arm and so 
shifts the brushes on the commutator to maintain a spark 
of about % in. on short circuit and % iii- at full load; 
at the same time the rheostat arm is moved over the con- 
tacts to cut resistance in, or out of the shunt around the 
field circuit. 



CONNECTIONS OF BRUSH CONTROLLER 




To Circuit or Plmrneter 



To Clutch a-fc P for Clockwise. 

To Clutch at E for Counter Clockwise. 



To Clutch at E for Clockwise. 
To Clutch at r for Coun<;.er Clockv** 
Changed 6 June '98. 



Fig. 475 

The current for the magnetic clutches is regulated by 
the controller. 

The controller consists principally of two magnets which 
are energized by the main current, and act when the current 
is too high or too low by sending a small current to one 
of the clutches. 

A careful examination of the controller (see Fig. 475). 
in connection with Fig. 474, will give a clear idea of it^ 



Operation of Dynamos 1095 

regulating action. It is generally advantageous to make 
the yoke which carries the brushes on the machines, and the 
arm moving the rheostat^ rather tight. As the magnetic 
clutches act with considerable force, it is not necessary to 
adjust these moving parts so loosely that they will move 
without considerable pressure on the rocker handle. Less 
difficulty will then be experienced in adjusting the con- 
troller. 

For shunt lamps, the controller may be adjusted to per- 
mit a variation of A ampere above or below normal; for 
differential lamps, the variation above and below normal 
should not exceed .2 ampere. The limits given in the fol- 
lowing instructions are for differential lamps, and may be 
extended .2 ampere above or below for shunt lamps. 

If the controller is out of adjustment and fails to keep 
the current normal, do not try to adjust the tensions of 
both armatures at the same time. For example, suppose 
the current is too high, either one of the two spools 
may be out of adjustment. The left-hand spool I may 
not take hold quickly enough, or the spool F may take 
hold too quickly. To make the adjustment, screw up the 
adjusting button K on the right hand spool, increasing the 
tension. This will have a tendency to let the current fall 
much lower before the armature comes in contact with H, 
to cause the current to increase. By simply tapping the 
armature G quickly with a pencil or piece of wood, forcing 
it down to its contact, and at the same time watching the 
ammeter, the current may be brought up to 6.8 amperes if 
6.6 amperes is normal, or to 9.8 if 9.6 amperes is normal. 
With the current at 6.8 amperes, which is .2 amperes high, 
the adjusting button L should be turned to increase the 
tension on this spring until the armature M comes in touch 
with contact N, which will force current down through 0. 



1096 Steam Engineering 

The clutch which pulls the brushes forward and rocks the 
rheostat back for less current will thus be energized. Re- 
peat this adjustment two or three times^ but do not touch 
the adjusting button K ; adjust L until it is just right. 

At the side of the armature M a little wedge is screwed 
in by means of an adjusting button^ and increases or 
decreases the leverage on this armature. See that this 
wedge is fairly well in between the core or frame of the 
spool and the spring of the armature. The armature M 
may have to be taken out and the spring slightly bent. 
It is advisable to have the screw which passes through the 
adjuster button L about half way in, to allow an equal 
distance up and down for adjusting this lighter spring 
after the wedge shaped piece is in the right position to 
give the necessary tension on the spring which is fastened 
to the armature M. 

In the right-hand corner P, a small bent piece of wire 
is placed for tightening up the screw which fastens the 
spring to the frame of the spool. As the contact made 
by the spring and the frame of the spool held together 
by a screw and button is a part of the magnetic circuit, it 
will be almost impossible to get this spring back to exactly 
the same tension after once removing it. Therefore, the 
adjusting buttons of the controller must be turned slightly 
in order to bring* it back to its proper adjustment. This, 
however, is an after consideration, and care should be 
taken to have the screw which holds the spring and frame 
together always tight. 

Having adjusted the spool I so that the current will 
not rise above 6.8 amperes (or 9.8 amperes), move the ar- 
mature M up to contact N with a pencil or piece of wood, 
causing the current to be reduced to about 6.2 (or 9.2). 
After the current settles at this point, decrease the tension 



Operation of Dynamos 1097 

on the spring which is fastened to armature G^ allowing 
this armature to fall down to contact H. Current will 
then flow through Q, which will rock the brushes back and 
also move the rheostat arm for more current. As the 
spool I has been adjusted for 6.8 (or 9.8) amperes, the 
current cannot rise above that amount no matter how the 
spool F is adjusted. 

With very little practice in moving the armature of 
one spool with a pencil;, the other can be adjusted much 
more readily than if an attempt is made to adjust the 
screws K and L at the same time. 

The two small shunt coils E and S^, are connected 
around the two contacts simply to decrease the spark be- 
tween the silver and platinum contacts. If they should 
become short circuited in any way^ so that their resist- 
ances become diminished^, sufficient cuirent may pass 
through eithei of them to operate the regulator. If unable 
to locate the trouble disconnect these coils at points T and 
U, when a thorough examination can be made. M and G- 
need not move more than just enough to open the con- 
tact ; 3^2 i^- is ample. 

In starting the machine^, the lower switch, which short 
circuits the field, should be opened last. 

The switch in the left-hand corner of the controller, 
Fig. 475, cuts out the two resistance wires which are used 
to force the current through wires and Q to the clutches. 
Open this switch, which leaves the automatic device of the 
controller in circuit, so that it will move the brush rocker. 
Unclamp the brush rocker from the rheostat arm rocker. 
Move the brushes by hand to give the proper spark, al- 
lowing the rheostat arm, however, to be moved by the con- 
troller. After the switches are opened, the rlieostat arm 
will go clear around to a full load position, and then, as 



1098 



Steam Engineering 



the current rises^ the controller takes hold and brings the 
arm back. In the meantime^ rock the brushes forward or 
backward and keep the sparK about the proper lengthy 
say % in.^ at full load to % in.^ on short circuit. Gradu- 
ally the rheostat arm will settle^ the spark will become con- 
stant^ and the machine will give its proper current. Then 
clamp the rocker and rheostat arm together and let the 
machine regulate itself. 

This method is much better than opening the switches 
on the machine, and allowing the wall controller to take 

PULLEY END COMMUTATOR END 




Fig. 476 



care of the machine from the start. By allowing the 
controller to start the machine, a trifle longer spark is ob- 
tained than by the other method, unless the machine is run 
from the beginning on a very full load. 

The machine will require a trifle longer spark on light 
load, or on bad circuits, than when running at full load. 
This fact shuld be borne in mind in wet weather, when 
trouble with grounds is experienced. 

A reliable ammeter should always be connected in the 
circuit of an arc generator,, so that the exact current may 



Operation of Dynamos 



1099 



be read at a glance. It should be connected into the nega- 
tive side of the line where the circuit leaves the regula- 
tor. 

The Thomson-Houston System. — The Thomson-Houston 
dynamo differs from other arc dynamos principally in the 
nature of its armature winding. This is shown in Fig. 476. 
One end of each of the three coils is connected to a copper 
ring common to all. The other end of each coil terminates 
at one of the three commutator segments. 




Fig. 477 



The following instructions regarding the management^ 
and operation of this machine may prove useful : 

Setting the Cut-out. — After the brushes are in position 
tlie cut-out must be set. This is done by turning the com- 
muntator on the shaft in the direction of rotation (if the 
commutator is set in position the whole armature must be 
revolved) until any two segments are just touching the 
primary brush on that side^ as segments A' and A"' touch 
brush B4 in Fig. 477. 



1100 steam Engineering 

Under these conditions brush B^ should be at the left- 
hand edge of upper segment. Then turn commutator until 
the same two segments are just touching brush B^^ when 
the end of Brush B^ should just come to the right-hand 
edge of the lower segment. If the secondary brush projects 
beyond the edge of the segment the regulator arm should 
be bent down; if it does not come to the edge of the seg- 
ment, the arm should be bent up. 

Care must be taken that the regulator armature is down 
on the stop when the cut-out is being set. These adjust- 
ments by bending regulatoi arm are always made in the 
factory before testing the machine, and should never be 
made on machines away from the factory, unless the regu- 
lator arm has been bent by accident. If it becomes nec- 
essary to make any adjustments they should be made by 
means of the sliding connection attached to the inner yoke. 

Always try the cut-out on both primary brushes. If it 
does not come the same on both, turn one over. If the 
brush-holders are correctly set by the guage, there should 
be no trouble in getting the cut-out set properly after one 
or two trials. 

To set the commutator in the proper position on a right- 
hand mxachine, with a ring armature, find the leading wire 
of No. 1 coil. Fig. 476. It is the custom in the factory to 
paint this lead red, also to paint a red mark on the center 
band between two groups of coils, namely, the last half 
of No. 1 coil and the first half of No. 3 coil. The first 
half of a coil is that group from which the lead comes. The 
last half is diametrically opposite the first half, and the 
lead wire belonging to it is connected with the brass ring 
on the outside of the connection disk on the commutator 
end. 



Operation of Dynamos 



1101 



In Fig. 478, the first halves of the three coils are rep- 
resented by 1^ 2 and 3, and the last halves by 1\ 2' and 3'. 

A narrow piece of tin with sharply pointed ends is bent 
Tip over the sides of the middle band at the center of the 
red mark so that the points are opposite each other. 

When the red mark and red lead have been founds turn 
the armature until the last half of No. 1 coil has AvhoUy 
disappeared under the left field and until the left-hand 







Fig. 478 



edge of the first coil to the right of the red mark (No. 3 
in Fig. 478) is just in line with the edge of the left field. 
The red lead will then be in position shown in Fig. 478 and 
the armature is in proper position to set the commutator. 
In the case of the right-hand drum armature, the lead- 
ing wire of the first coil should be found. This lead may 
be recognized from the fact that it is more heavily insul- 
ated than the rest, and is found in the center of the outer 



1102 



Steam Engineering 



coil^ on the commutator end. With this wire turned under- 
neath, rotate the armature forward^ or counter-clockwise, 
until the pegs on the right-hand side of this coil just dis- 
appear under the left field. (See Fig. 479.) 

The position of the red lead and the red mark on the 
band are the same on all armatures^ but their positions in 
the fields of the machines called left-hand (clockwise ro- 




FiG. 479 



tation), should be as shown in Pigs. 480 and 481 when set- 
ting the commutator. 

When the armature of a right-handed machine is in 
position^ the commutator is turned on the shaft until seg- 
ment No. 1 is in the same relative position as the last half 
of No. 1 coil; segment No. 2 should correspond with the 
last half of No. 2 coil^, and segment No. 3 with the last 
half of No. 3 coil, as shown on Figs. 478 and 479. 

For left-hand machines, see Figs. 480 and 481. 



Operation of Dynamos 



1103 



The distance from the tip of the brushy which is on 
top, to the left-hand edge of No. 2 segment on a right- 
hand machine, or to the right-hand edge of No. 3 segment 
in a left-hand machine is called the lead, and should be 
made to correspond with the following table. 




Red mark pairtt^aci 
orv ceot^er iaarvcU 



Fig. 480 



TABLE 
DRUM ARMATURES. 

0^2 1^ inch positive 
C2 % inch positive 
W^ -^^ inch positive 
E^ % inch positive 
H^2 1^ inch positive 
H2 1/4 inch positive 



OF LEADS. 



RING ARMATURES. 

K^2 t\ inch positive 
K2 % inch positive 

M2 

LD12 

LD2 1/^ inch positive 
MD12 i| inch positive 
MD2 ^1 inch positive 



1/4 iiich negative 
% inch negative 
1/4 inch positive 



1104 



Steam Engineering 



Place the screws in the binding posts at the lower ends 
of the sliding connections^ and put on the dash pot con- 
nections between the brushes, with the heads of the con- 
necting screws outward. In every case the barrel part of 
the dash pot is connected to the top brush-holder, and 
plunger part to the bottom brush-holder. 

See that the field and regulator wires are connected 
^nd that all connections are securely made. 




Fig. 481 



When all connections have been made, make a careful 
'examination of screws. Joints and all moving parts. They 
must be free from stickiness, and bind in any position. 

To determine when the machine is under full load, notice 
the position of the regulator armature, which should be 
within % in. of the stop. At full load the normal length 
of the spark on the commutator should be about 3/16 in. 
If it is less than this, shut down the machine and move 
the commutator forward or in the direction of rotation 



Operation of Dynamos 



1105 



until the spark is of the desired length. If the spark is 
too long^ move the commutator back the proper amount. 

A general view of the complete dynamo is given in Fig. 
482, and will help explain the regulator used with this 
system. 

The regulator is fastened to the frame of the machine 
by two short bolts. On the right-hand machine its posi- 




FiG. 482 



tion is on the left-hand side, as shown in Fig. 482. On 
the left-hand machine, i, e., one which runs clockwise, its 
position is on the opposite side. Before filling the dash 
pot D with glycerine, see that the regulator lever and its 
connections, brush yokes, etc., are free in every joint, and 
that the lever L can move freely up and down. Then fill 
the dash pot D with concentrated glycerine. The long wire 



1106 



Steam Engineering 



from the regulator magnet M is connected with the left- 
hand binding post P of the machine^ and the short wire 
with the post P^ on the side of the machine. The inside 
wire of the field magnet^ or that leaving the iron flange, 
of the left-hand field should be connected into post P^ 
also, as shown in Fig. 482. The electric circuit (see Fig. 
483) should be complete from post P^, on the controller 
magnet, through the lamps to the post K on the machine, 
through the right-hand field magnet C, to the brushes 




Fig. 483 

B^B^, through the commutator and armature to the brushes 
B B, through the left-hand field C, to posts P^ and P, 
thence to posts P^ and P on the controller magnet, through 
the controller magnet to P^ The current passes in the 
direction indicated by the arrows. 

When an arc machine is to be run frequently at a small 
fraction of its normal capacity, the use of a light load 
device is advisable to secure the best results in regula- 
tion. 



8izi 



Operation of Dynamos 



1107 



The rheostat for this purpose (see Fig. 484) is connected 
in shu|it with the right field of the generator. Facing 
the rheostat with the right binding posts at the bottom^ 
the contact on the right side or No. 1 gives open circuit 
and throws the rheostat out of use.. Point No. 2 gives a 
resistance of 44 to 46 ohms and Point No. 3 gives a re- 
sistance of 20 to 22 ohms. 

This rheostat with a 75-light machine allows the fol- 
lowing variations: Point 1, 75 to 48 lights; Point 2, 48 to 




Fig. 484 



25 lights; Point 3^ 25 lights or less. For use with other 
sizes of generators^ the adjustment of the rheostat must be 
fmade to suit the conditions. 

When the rheostat is in use^, the sparks at the commuta- 
tor will be somewhat larger than normal^ but will not be 
'detrimental. 

The controller magnet (see Fig. 485) is to be fastened 
securely by screws to the wall or some rigid upright sup- 
port, taking care to have it perfectly plumb. It is con- 



1108 



Steam Engineering 



nected to the machine in the manner shown in Fig. 482, 
i. e., the binding Post P^ on the controller magnet is con- 
nected to the binding post P^ (see Fig. 482) on the end 
of the machine, and likewise the post P on the controller 
to the post P on the l6g of the machine ; the post P^ forms 
the positive terminal from which the circuit is run to the 
lamps and beck to N*. 




eoi 



t 



Great care should be taken to see that the wires P P 
a,nd p2 P2 are fastened securely in place; for if connec- 
tion between P and P should be impaired or broken, the 
regulator magnet M would be thrown out of action, thus 
throwing on the full power of the machine, and if the 



Operation of Dynamos 1109 

wire P2 P2 should become loosened^ the full power of the 
magnet M would be thrown on^ and the regulator lever 
L^ rising in consequence^ would greatly weaken or ^ put out 
the lights. 

The wires leading from the controller magnet to the ma- 
chine should have an extra heavy insulation. 

Care should be taken in putting up the controller mag- 
net that the following directions are followed: 

1. The cores B of the axial magnets C C must hang 
exactly in the center^ and be free to move up and down. 

2. The screws fastening the yoke or tie pieces to the 
two cores must not be loosened. 

3. The contacts must be firmly closed when the cores 
are not attracted by the coils C C^ which is the case^, of 
course^ when no current is being generated by the machine, 
and when the cores are lifted^ the contacts must open from 
1/64 in. to 1/32 in. ; a greater opening than 1/32 in. has 
the effect of lengthening the time of action of the regula- 
tor magnet. This tends to render the current unsteady, 
and in case of a very weak dash pot^ or short circuit might 
cause flashing. Adjustment must be made if necessary 
by bending the lower contact up or down^ taking care that 
it is kept parallel with the upper contact, so that when they 
are closed, contact will be made across its whole width. If 
this adjustment is not properly made there will be destruc- 
tive sparking on a small portion of the contact surfaces. 

4. All connections must be perfectly secure. 

5. The check nuts IST must be tight. 

6. The carbons in the tubes L must be whole. These 
-; carbons form a permanent shunt of high resistance around 
3 the regulator magnet M, and if broken will cause destruc- 
^ tive sparking at contacts 0, burning them and seriously 
ii interfering with close regulation of the generator. In case 



1110 steam Engineering 

a carbon should become broken, temporary repairs may 
be made by splicing the broken pieces with a fine copper 
wire. 

To keep the action of the controller perfect the contacts 
should be occasionally cleaned by inserting a folded 
piece of fine emery cloth and drawing it back and forth. 

The amount of current generated by each machine de- 
pends upon the adjustment of the spring S. If the 
tension of this spring is increased, the current will be di- 
minished, if the tension is diminished the current will be 
increased. 

In starting these dynamos when the armatare has 
reached its proper speed, the short circuiting switch on 
the frame should be opened. This method allows the 
generator to take up its load gradually, and is a ve'^y im- 
portant point in the handling of the machine. 

ELECTRIC MOTORS. 

The doctrine of the conservation of energy alreadv re- 
ferred to in this volume, may safely be regarded a^ the 
corner stone of engineeriijg science, and in nothing ij5 it 
better illustrated than in the reversibility of the dyneano, 
and motor. When the armature of a dynamo is cai?^ed 
ta revolve within the field of force, by mechanical power, 
resistance will be encountered if the circuit is closed, and 
the result is that the mechanical energy is absorbed, and 
converted into electrical energy, the presence of which is 
easily detected by the heating the wires, and other means. 
Energy is conserved. 

In the electric motor, this action is .exactly reversed. 
Electrical energy is absorbed, and mechanical energy is 
supplied by it. In engineering practice an electric ma- 



Electric Motors 1111 

chine (dynamo or motor )^ often automatically changes 
from motor to dynamo^ or the reverse^ and in some cases 
serious trouble results, if the change is not detected in 
time. 

Any dynamo may be used as a motor and consequently 
we have as many types of motors as there types of dy- 
namos. The pull of a motor depends upon the repulsion 
and attraction between the lines of force, or magnetism of 
the wire/ and core of the armature, and that of the fields. 
We have seen that in a dynamo, as we force a wire through 
a magnetic field, current is generated. . The more current 
there is generated, or flowing in such a wire, the greater 
will be the expenditure of power necessary to force such 
a wire through a magnetic field; in other words^ the cur- 
rents flowing in the wires of a dynamo armature, always 
tend to drive the armature in a direction opposite to that 
in which it is being driyen. 

If, then, instead of revolving a dynamo armature by 
machanical means, we connect it to a source of electricity 
and allow a current to flow through it we must obtain 
motion, and the direction of this motion will depend upon 
the direction in which the current flows, so long as this 
current does not alter the magnetism of the fields. 

The electric motor is built exactly like a dynamo; con- 
sequently, as its armature revolves it not only does useful 
work, such as turning whatever machinery it is belted to, 
but it also generates an electromotive force. For instance, 
if a motor, running at full speed and receiving current 
from a dynamo (Fig. 486), were suddenly disconnected by 
opening the main switch, it would at once begin acting as 
a generator and sending out current. This can be easily 
seen with any motor equipped with a starting box, such as 



1112 



Steam Engineering 



shown; for the current from the motor will continne to 
energize the fields^ and the little magnet M so as to hold the 
arm of the starting box nntil the motor has nearly eome to 
rest. If it were not for the current generated by the motor, 
this arm would fly back the instant the switch is onened. 




Fig. 486 

The electromotive force set up by a motor always op-l^i 
poses that of the dynamo driving it; that is^ the currenti 
which the motor tends to send out would flow in the op- 
posite direction to that which is driving it. 

This may be compared^ and is somewhat . similar, to 
the back pressure of the water which a pump is forcing into 
a tank. If the check valvfes were removed and the steam 



of 



Electric Motors 1113 

pressure shut off^ the water would tend to force the pump 
backward. 

This electromotive force is called the counter electro- 
motive force of the motor. The counter electro-motive force 
of the motor varies with the speed of the motor, and also 
limits the speed of the motor, for it is obviously impossible 
that a motor should develop higher counter E. M. P. than 
the E. M. P. of the dynamo driving it. 

The highest possible speed of a motor is^ then, that 
speed at which its counter E. M. F. becomes equal to the 
E. M. P. of the dynamo supplying the current, and this is 
the speed which would be obtained were the motor doing 
no work and running without friction. This condition 
is impossible in practice, and the counter E. M. P. of the 
motor is always less than the E. M. P. of the dynamo. To 
speed up a motor it must run faster in order to develop 
jan E. M. P. equal to that of the dynamo. This may be 
done by lessening the number of turns of wire on the ar- 
mature, or by lessening the magnetism of the fields. In 
doing so, however, the capacity of the motor for per- 
forming work is also lessened. 

The power that can be obtained from an electric motor 
.depends upon two things: the current flowing in its ar- 
1 mature coils, and the strength of magnetism developed in 
the fields. 

Assuming the fields as remaining constant, the power 
of the motor must then vary as the current flowing through 
it. Suppose we have a motor being driven by an E. M. P. 
of 110 volts and it is doing no work; it will be running at 
full speed and its counter E. M. P. will therefore also be 
very near 110 volts. If now a load be thrown on this mo- 
'tor, it must get more current in order to develop the nec- 
essary power to carry the load. 



1114 Steam Engineering 

Throwing on the load will decrease the speed of this 
motor^ and consequently its counter E. M. P. will fall^ 
say to 100 volts. The E. M. F. of the dynamo being 110 
and the counter E. M. P. of the motor 100, there will be 
considerable current forced through the armature of the 
motor, so that it can now handle the load. 

The current in the armature at all times will equal 

E — E' 

where E is the electromotive force of the dy- 

namo, E' the counter electromotive force of motor^ and R 
the resistance of the motor armature. In order that a 
motor should keep a nearly uniform speed, for varying 
loads, the resistance of its armature should be very low, 
for then a slight drop in counter E. M. F. will allow con- 
siderable current to flow through the armature. The above 
applies particularly to the shunt motor shown in Fig. 486. 
In this diagram C is a double pole fuse block, S the main 
controlling switch, E the starting box, or rheostat, M the 
magnet, which holds the arm of the starting box in place 
when it is brought over against it, P the fields, and A 
the armature of the motor. 

The current enters, say at the right hand fuse, and 
passes to the starting box and along the fine wires shown 
in dotted lines through the fields of the motor and coil 
M to the other fuse. The fields of the motor and the little 
magnet M are now charged, but as yet there is no current 
passing through the armature and no motion. We now 
slowly move the arm on the starting box to the right; 
this admits a little current, limited by the resistance in 
the starting box, to the motor armature and it begins to 
revolve, and as we continue to move the arm to the right, 
the armature gains in speed because we admit more current 



Electric Motors 



1115 



to it by cutting ont more and more resistance. When the 
armature attains full speedy the arm comes in contact 
with the little magnet M, and is held there by rnagnetism. 
The whole object of the starting box is to check the inrush 
of current, while the armature is developing its counter 
E. M. F. or back pressure. 




When the armature has attained its normal speed, the 
starting box is no longer in use. If for any reason .the 
current ceases to flow, the little magnet M loses its magnet- 
ism and releases the arm, which (actuated by a spring) 
flies back and opens the circuit so that, should the current 
suddenly come on again, the sudden inrush will not damage 
the armature. 



1116 



Steam Engineering 



In Fig. 487 are sho^ni the connections of a series wound 
motor with an automatic release spool on the starting box 
of a sufficiently high resistance so that it can be connected 
directly across the circuit. This becomes necessary since 
the field windings are in series with the armature. 

The speed of a series motor may be decreased by connect- 
ing a resistance in series with the motor^ and may be in- 




Fig. 4S8 

creased in speed by cutting out some of the field windings. 
In electric railway work where two motors are used on one 
car^ they are usually connected in series with each other 
in starting up^ and then in parallel with each other while 
running at full or nearly full speed. The series motor is 
well adapted to such work as electric railway work, or for 



Electric Motors 1117 

cranes and so forth^ because it will antomatically regulate 
its speed to the load to be moved^ exerting a powerful 
torque at a low speed while pulling a heavy load. Such a 
motor^ however^ requires constant attendance when the 
load becomes lights as it will tend to ^^run away^^ unless 
its speed is checked. 

In Fig. 488 we have a diagram of a compound wound 
motor connected with a type of starting box that cuts 
out the armature when current has been cut off the lines 
supplying the motor^ as before explained. In addition to 
this there is another electro magnet which is traversed 
by the main current on its path to the armature. Should 
the motor be overloaded by some means^ the current flow- 
ing to the armature would exced the normal flow. The 
magnetism thus produced would overcome the tension of 
a spring" on the armature of the so-called '^^overload mag- 
net^^ and cause it to short circuit the magnet which holds 
the resistance lever, and allow it to fly back and open the 
armature circuit. By so doing the liability of burning out 
the armature due to overload is reduced to a minimum. 

The compound motor may be made to run at a very 
constant speedy if the current in the series winding of the 
fields is arranged to act in opposition to that of the shunt 
winding. In such a case an increase in the load of a 
motor will weaken the fields and allow more current to* 
flow through the armature without decreasing the speed 
of the armature^ as would be necesary in a shunt motor. 
Such motors, liowever, are not very often used, since an 
overload would weaken the fields too much and cause 
trouble. 

I£ the current in the series field acts in the same direc- 
tion as that of the shunt fields^ the motor will slow up 
some when a heavy load comes on, but will take care of 



1118 



Steam Engineering 



the load without much t-rouble. Fig. 489 shows a start- 
ing box arranged as a speed controller. It differs from 
other starting boxes only in so far that the resistance wire 
is much larger^ and that the little magnet will hold the arm 
at any place we desire^, so that if we leave the arm at any 




Fig. 4S9 

intermediate point the motor will run at reduced speed. 
This sort of speed regulation can be used only where the 
load on the motor is quite constant. If the load varies, the 
speed will vary. Another ' and a better way of varying 
the speed of motors consists in cutting a variable resist- 



Electric Motors 1119 

ance into the field circuit, because as more resistance is 
cut into the circuit the fields become weaker and the motor 
speeds up. If possible, motors should be so designed that 
they can operate at their normal speed, and they will then 
cause little trouble. 

Motors have much the same faults as dj^namos, but they 
make themselves manifest in a different way. An open 
field circuit will prevent the motor from starting, and will 
cause the melting of fuses or burning out of an armature. 
The direction of rotation can be altered by reversing the 
current through either the armature or the fields. If the 
current is reversed through both, the motor will continue 
to run in the same direction. A short circuit in the fields, 
if it cuts out only a part of the wiring, will cause the mo- 
tor to run faster and very likely spark badly. If the 
brushes are not set exactly opposite each other, there will 
also be bad sparking. If they are not at the neutral point, 
the motor will spark badly. Brushes should always be 
set at the point of least sparking. If it becomes neces- 
sary to open the field circuit, it should be done slowly, 
letting the arc gradually die out. A quick break of a 
circuit in connection with any dynamo, or motor is not 
advisable, as it is very likely to break down the insulation 
of the machine. 

The ordinary starting box for motors is wound with 
comparatively fine wire and will get very hot if left in cir- 
cuit long. The movement of the arm from the first to 
the last point should not occupy more than thirty seconds, 
and if the armature does not begin to move at the first 
point the arm should be thrown back and the trouble lo- 
cated. 

Alternating Current Motors. — By a proper combination 
of two phase or three phase currents it is possible to pro- 



1120 



Steam Engineering 



duce a rotating magnetic pole. By placing inside of the 
apparatus which produces this rotating magnetic pole, a 
suitable short circuited armature, this armature will be 
dragged around by the rotating pole in much the same 
way that a short circuited armature in a direct current ma- 
chine would be dragged around if the fields were revolved. 
Such a machine is called an induction motor. The arma- 
ture will revolve without any current entering it from the 
external circuit. This does away with commutators, collec- 
tor rings, brushes, brush-holders, and in fact many of the 
parts which are so necessary in direct current machines. 

6 B 




The rapidity of the alternations in the external circuit de- 
termines the speed of the motor. 

Synchronous Motors. — Some alternating current motors 
are known as ^"^synchronous^^ motors. What is meant by 
synchronous is, occurring at the same time, or in unison. 
As an example, suppose two clocks are ticking just alike 
so that the pendulums start and stop at the same time; 
we would hear but one tick. These two clocks would then 
be in synchronism. If an alternating current generator 
has 32 field coils and revolves-at the rate of 60 E. P. M., 
then a synchronous motor with only 4 field coils would re- 
volve at the rate of 480 E. P. M. This motor would op- 



Electric Motors 1121 

erate in synchrony with the generator^ and yet would make 
480 E. P. M. while the generator made 60 E. P. M. 

The production of the rotary field is the main reason 
for the generation of polyphase currents. 

Fig. 490 shows four coils of wire. Assume that the 
coils B B receive an alternating current, and the coils A A 
receive another current in quadrature with the first. Then 
when the current in B B is at maximum, the current in 
A A will be at minimum, and as the current in B B de- 
creases, the current in A A will increase. 




Fig. 491 
two phase rotating field coil and armature 

When the B current is at maximum, there will be es- 
tablished N and S magnet poles on a horizontal axis pass- 
ing through the center of the B coil. The A coils when 
active will establish poles on an axis perpendicular thereto. 

Poles at intermediate points will also be established 
when current is passing through all four coils. The result 
of this arrangement is that north and soutli poles are kept 
traveling around the circle by the alternating currents 
acting in quadrature with each other, meaning that the 
angle of lag and lead between the two current waves is 
90° or a quarter circle. 



1122 



Steam Engineering 



Currents of this kind constitute a two phase alternating 
current and the changes occur about 100 times per second. 
Fig. 491 shows a cylindrical laminated core wound with a 
re-entrant coil, and mounted on bearings within the field. 
This core will rotate because the alternating currents 
passing through the field coils will induce currents in its 
wires, owing to their rotary field of force. 

In order to establish in the core the polarity above de- 
scribed, the lines of force must be cut by its windings. 
Consequently it lags behind, and its revolutions per minute 




R 

IVIOTOR 

Fig. 492 
three phase generator, and induction motor 

are from 5 to 10 per cent slower than those of the rotary 
field. If it were made to synchronize with the field it would 
have no induced polarity, and no pull or torque would be 
exerted upon it. Therefore, it constantly falls behind, 
and the amount of this drop is termed its slip. Fig. 492 
is a diagrammatic view of the generation of a three-phase 
current, and the operation by it of an induction motor. 
Following the lines and numbers will show that the stator 
of the motor receives the same currents that are induced in 
the stator of the generator. 



Electric Motors 



1123 



But the poles of the generator travel around it, the 
result being that a rotary field is produced in the stator of 
the generator. Pig. 493 represents a four-pole, three- 
phase generator driving such a motor. 

There are 12 armature coils, three sets marked A, B, C, 
for each pole of the generator, thus giving a three-phase 
current. They are oonnected in Y combination. The gen- 
erator is shown on the left, the field being the rotor. 

The motor is shown on the right of the diagram, and it 
also has 12 coils marked as in the generator, and Y con- 




FiG. 493 

FOUR-POLE THREE-PHASE GENERATOR AND INDUCTION MOTOR 

nected. The generator and motor are connected by the 
three wires a, b, and c, the fourth wire being omitted, as 
it would have no load to carry. The large letters on the 
[armature indicate the course of the windings. The three- 
phase current produces a rotary field, on the same general 
principle as does the two-phase current. Tlie lag of the 
currents behind each other acts to cause the poles resulting 
from the combined action of the coils, to rotate around 
the field. Motors constructed upon this principle are 
termed induction motors, and the coils on the armature 
1 (which is the rotor), are self-contained, having their ter- 



1124 



Steam Engineering 



minals connected so that the winding is re-entrant, and 
has no ontside connection whatever. Fig. 494 shows such a 




Fig. 494 

INDUCTION MOTOR WITH SQUIRREL CAGE ARMATURE 

motor complete. The rotary field referred to in the fore- 
going description should not be confounded with the re- 




FiG. 495 

SQUIRREL CAGE ARMATURE 



volving field. In the rotary field the rotary action is purely 
electrical, the poles simply rotating around the circle, there 
being no rotation of any part of the mechanism. But a re- 



Questions and Answers 1125 

volving field is entirel}^ different. It revolves on an axis 
like a wheel. The student should remember this^ as there 
is danger of confusion in the use of the two terms. A 
combined rotary^, and revolving field may be obtained by 
a simple modification of the mechanical structure^ in which 
the field is mounted on journals^ and the armature is 
stationary. Fig. 495 shows the squirrel-cage armature of 
an induction motor^ the core being laminated^ and having 
straight conductors of copper lying in the longitudinal 
grooves close to its surface. The ends of these conductors 
are connected to two rings of copper. 

QUESTIONS AND ANSWEES. 

714. What is electricity? 

Ans, Electricity is an invisible agent. Its exact na- 
ture is not very well known^ although the laws govern- 
ing its action^ the methods of controlling it^ and the ef- 
fects produced by it are becoming well known. 

715. Is it correct to use the term quantity with refer- 
ence to electricity? 

Ans. It is. We may use terms to designate definite 
quantities of electricity^ passing through a conductor, in the 
same way that we speak of gallons of water flowing through 
a pipe. 

716. Is it proper to assume that there are large quanti- 
ties of electricity stored for future use^ in a manner similar 
to water? 

Ans. It is not, except in a limited sense, as in storage 
batteries. 

718. Define the doctrine of the conservation of energy. 



1126 Steam Engineering 

Ans. The total qnantity of energy in the universe is 
unalterable. When energy is expended, or disappears in 
one form, it must reappear in another form. 

719. In accordance with this doctrine, what would be 
the proper term to apply to electricity with reference to 
the physical requirements of man? 

Ans. It is a useful agent for the rapid transmission of 
stored up energy in fuel, water falls, etc. 

720. What is the practical unit of quantity used in 
speaking of electricity? 

Ans, The coulomb. It is that quantity of electricity 
that would pass in one second through a circuit carrying a 
current of one ampere. 

721. What is an ampere? 

Ans, It is the unit of volume, or rate of flow. A cur- 
rent of one ampere will flow through a circuit whose re- 
sistance equals one ohm, when the electro-motive force, or 
pressure behind it equals one volt. 

722. What is a volt? 

Ans, The volt is the unit of electro-motive force, and 
represents a pressure that will cause the flow of one am- 
pere through a circuit in which the resistance equals 
one ohm. 

723. What is an ohm? 

A71S, The ohm is the practical unit of electrical resist- 
ance. It is that araount of resistance that would limit the 
flow of electricity under an electromotive force of one 
volt, to a current of one ampere, or to a discharge of 
one coulomb per second. It equals the resistance of a 
column of mercury one sq. millimetre in area of cross sec- 
tion, and 104.9 centimetres in length. 

724. What is the unit of work? 
Ans, The foot pound. 



Questions and Answers 1127 

725. What is the nnit of power^ or rate of doing work? 

Ans. The foot pounds per second. 

H26. How is the amount of work that electricity is ca- 
pable of doing, measured ? 

Ans. By the volt-conlomb, or Joule. The amount of 
electrical work per second is, equal to the volt ampere, or 
watt. 

'?27. What amount of power developed is represented 
by the watt ? 

Ans, M.25 foot-lbs. of work per minute, or 0.7375 foot- 
lbs, per second. 

728. What is a magnet ? 

Ans, A mineral consisting of a combination of iron and 
oxygen. 

729. What is the chemical formula of a magnet? 
Ans, Fe^O^. 

730. What is a permanent magnet? 

Ans, A piece of steel that has been charged with mag- 
netism, and retains it. 

731. What is meant by the poles of a magnet? 

Ans, All magnets tend to point north and south, the 
same end always pointing in the same direction ; hence the 
end pointing north is called the north pole, and the end 
pointing south is termed the south pole. 

732. What peculiar characteristic attaches to the poles 
of magnets ? 

Ans, The north poles of two magnets tend to repel 
each other, and the same is true of the south poles. But 
the north pole of one magnet attracts the south pole of an- 
other, like repels like, and unlike attracts unlike. 

733. What is an electro mas^net? 

Ans, A bar of iron surrounded by a coil of wire through 
which an electric current is passing. 



} 



1128 Steam Engineering 

734. What are lines of force? 

Ans, The}^ are certain imaginary lines passing through 
the steel of the magnet from its south pole to its north pole^ 
and issuing from the latter they curve around through 
space and return to the south pole. 

735. What is the magnetic circuit ? 

Ans. It is the path of these lines of force, around and 
through the magnet. It resembles a closed curve, either a 
circle, or an ellipse. 

736. Explain the difference between the magnetic cir- 
cuit and the electric circuit. 

Ans. The magnetic circuit, or field of force, that sur- 
rounds a magnet is maintained without the expenditure of 
energy, while on the other hand an electric current passing 
upon its circuit develops energy, and energy must be ex- 
pended to maintain it. 

737. Are there any other points of difference between 
the two circuits. 

Ans. Yes, the electric current passes through a con- 
ductor in intensity proportional to the electro-motive force 
urging it, while the magnetic circuit passes through air, 
or a vacuum in proportion to the magneto-motive force 
urging it. 

738. What is meant by the term potential as applied in 
electric practice ? 

Ans. Voltage or pressure. 

739. What is the law of induction? 

Ans. When a conductor is moved in a magnetic field 
of force so as to cut the lines of force, there is an electro- 
motive force impressed on the conductor in a direction at 
right angles to the direction of motion, and at right an- 
gles to the direction of the lines of force. 

740. What is a dynamo? 



Questions and Answers 1129 

Ans. A machine for transforming mechanical energy 
into electrical energy. 

741. How is the field of force maintained in a dynamo ? 

Ans, By means of electro-magnets. 

742.' Does not this require the expenditure of energy? 

Ans. Yes; a certain amount of energy is indirectly ex- 
pended. 

743. How are dynamos classified? 

Ans, Into two grand divisions^, viz., direct current dy- 
namos and alternating current dynamos. 

744. What is direct electrical current? 
Ans. A current of unchanging direction. 

745. What is an alternating current ? 

Ans. A current that reverses its direction of flow, pe- 
riodically, from 20 times and upward per second. 

746. Name the principal constituent parts of a dy- 
namo. 

Ans. The armature, the field, the collecting rings, or 
commutator, and the brushes. 

747. How is electro motive force or current induced in 
a dynamo? 

Ans. By rapidly changing field and armature relations 
by means of mechanical energy. 

748. How is the output of a dynamo stated? 

Ans. In Kilowatts equal to 1,000 X volts X amperes. 

749. How is the output of a motor stated? 

Ans. In horse power, equal to Watts intake -f- 746 Xef- 
ficiency expressed decimally. (Not as a percentage.) 

750. What is the voltage of a dynamo? of motor? 
Ans. It is the pressure that the generator or alternator 

delivers at its own terminals. The voltage of a motor is the 
voltage which should be applied to its terminals in order 
to develop full horse power. 



1130 Steam Engineering 

751. What is full load current of dynamo? of motor? 
Ans, Full load current of a dj^namo is that current 

which may be drawn steady for 24 hours without causing 
any part of the machine to exceed a safe temperature, i. e.. 
15jp^ Fahr. This applies to factory motors. 

752. What is meant by the rating- of a dynamo? Of a 
motor ? 

Arts, The product of full load current multiplied by 
the voltage expressed in Kilowatts is rating of a dynamo. 
The actual mechanical horse power developed at the pinion 
of the motor as tested in shop. 

753. AYhat is the armature core? 

Ans, The sheet iron body which carries the armature 
winding, and conducts the flux from pole piece to pole piece. 

754. What is the armature spider ? 

Ans, The casting consisting of hub and arms which 
supports armature core. 

755. What are binding wires? 

Ans, They are narrow bands of phosphor bronze wire 
placed around the armature every three or four inches to 
help bind the winding to the core. They rest on strips of 
mica, and are sweated with solder all around. 

756. What are commutator segments? 

Ans. The commutator segments or bars are the copper 
pieces of which the commutator is built. 

757. A^Hiat are commutator leads? 

Ans. They are the ends of the armature winding ex- 
tending from the core to the lug of the commutator bar. 

758. What are pole pieces? 

Ans. The end of the magnet core nearest the armature. 
Usually larger than the core. 

759. What are magnet cores? 
Ans. The iron inside the field coil. 



Questions and Answers 1131 

760. What is the yoke? 

Ans, The part of magnetic circuit connecting the mag- 
net cores. 

761. What is the pitch of an armature winding? 

Ans. It is the number of teeth between the two sides of 
a formed coil plus one tooth. 

Example : The two sides of a coil are in slots number 
3 and 17, then pitch is 14. 

762. Is there insulation between winding and core ? 
Ans. Yes. Mica or fuller board ; there is also the tape 

on coil. 

763. What insulation is there between conductors of 
winding ? 

Ans. The double cotton covering of each wire makes 
four thicknesses between conductors. 

764. What is the air gap? 

Ans. It is the air space between armature and pole 
pieces. In dynamos it is made as small as possible for ef- 
ficiency. 

In motors it is not made too small because this tends to 
make the machine spark due to the weak field. In D. C. 
series motors it is from % to i/4 of ^^ inch, in A. C. series 
motor it is smaller, say 1/10 to % inch. 

The larger the air gap of a motor the more the bearings 
may wear before there is danger of the armature rubbing 
against the lower pole pieces. 

765. What are field spools? 

Ans. The brass shells on which the field coils are 
wound. 

766. What is the commutator? 

Ans. It is a series of copper bars placed parallel to 
the shaft, insulated from each other and from the frame of 
the machine. Each is connected to the windino^ and cur- 



1132 Steam Engineering 

rent flows from the winding through them to the brushes. 
It at the same time reverses the connections between the 
brushes and the winding at the proper times so that the 
brush always collects current. 

767. What is a collector or slip ring? 

Ans. A collector consists of two or more rings of copper 
placed around the shaft and insulated from it^ and each 
other. Each is connected to a part of the winding. The 
brushes rest on the rings. 

They are used to collect current from a revolving arma- 
ture style of alternator^ to feed current into armatures of 
rotary converters, or the revolving fields of alternators. 

The collector has no corrective influence and passes on 
the A. C. or D. C. current exactly as it receives it. 

Single phase machines have two rings; two^ three, and 
six phase machines have three rings. 

768. Is there a difference between no load and full load 
voltage of dynamos? 

Ans. Yes. A shunt dynamo gives highest voltage at no 
load and lowest at overloads ; the series dynamo gives lowest 
at no load and highest at full load. The compound dj^"- 
namo is a combination of series and shunt, and gives same 
voltage at all loads. 

An alternator acts like a shunt dynamo. 

769. What is a field rheostat ? 

Ans, It is a resistance in the field circuit which can be 
varied to change the current, and hence the field strength. 
This alters the voltage of the dynamo. 

770. What are commutated fields? 

Ans. In some motors the field coils are arranged in sec- 
tions so that they may be arranged in parallel, or series, or 
in combinations. 



Questions and Answers 1133 

All coils in parallel give the greatest current and hence 
slowest speed of motor; all coils in series give the weakest 
field and the fastest speed. 

771. What relation has field strength to the speed ol 
motor ? 

Ans, The weaker the field the faster the speedy for the 
motor mnst revolve fast to generate its proper counter 
E. M. F. 

772. What relation has armature strength to the speed 
of motor ? 

Ans. The greater the armature current the higher the 
speed. 

773. What effect on the power of motor does field, and 
armature strength have? 

Ans. The greater the field and armature current the 
greater the power. 

774. What is a ring winding? 

Ans. One which passes over and under around the core, 
a space being left between the shaft and core to accommo- 
date the winding. 

775. What is a drum winding? 

Ans. One where all winding is on the outer surface of 
the core. 

776. Upon what does sparkless commutation of current 
depend ? 

Ans. (1) The more commutator bars the better, there 
being less voltage and therefore tendency to spark between 
bars. The average railway motor has from 100 to 125 
bars on commutator. 

(2) The fewer the ampere turns on the armature in 
comparison to the ampere turns on the field the less spark- 
ing. 



1134 Steam Engineering 

(3) The more turns short-circuited by the brush wheQ 
touching two or more bars at once^ the greater the tendency 
to spark. 

777. What is a shunt field? 

Ans. One whose coils are placed as a shunt across the 
brushes. It carries a small current. 

778. What is a series field? 

Ans, One which carries the main, or nearly all the 
main current^ and is placed in series with the armature. 
A small strip of resistance metal is used sometimes to di- 
vert a portion of the main current from the series field. 

779. What are Foucault;, or eddy currents? 

Ans. Local currents set up within the armature, and 
acting as a hindrance to the generation of useful current. 

780. How may the electro-motive force be increased ? 
Ans. By increasing the speedy or by adding more turns 

or loops of wire to the armature winding. 

781. What is meant by self excitation of a dynamo? 

Ans. When the dynamo is standing stilly the field mag- 
nets become weakly magnetic^ but when the armature begins 
to revolve a few volts of electric current will be sent through 
the field coils, gradually increasing the magnetic strength 
until full voltage is reached. 

782. What is a series dynamo ? 

Ans. One in which the same current that travels the 
main circuit also traverses the field. 

783. Explain the action of the shunt djoiamo. 

Ans. The field circuit is a shunt, and only a portion of 
the main current passes through it. 

784. How are the fields of a compound dynamo ex- 
cited ? 



Questions and Answers 1135 

Ans. The fields have two distinct windings ; one shunt, 
and the other series. 

785. What advantage pertains to the compound wound 
dynamo ? 

Ans. It is practically self-regulating. 

786. What is the difference between the dynamo and 
the electric motor? 

Ans, Practically none in the principles governing the 
design of the machines. Any dynamo may be used as a 
motor, and vice versa. 

787. State the difference in their functions. 

Ans. The dynamo converts mechanical energy into elec- 
trical energy, while the motor converts electrical energy 
into mechanical energy. 

788. Upon what does the power to be obtained from 
a motor depend? 

Ans, Two things, viz., the current flowing in its arma- 
ture coils, and the strength of magnetism developed in its 
fields. 

789. How is the speed of motors controlled? 
Ans, By a starting box or rheostat. 

790. How may the direction of rotation of a motor 
be reversed? 

Ans, By reversing the current through either the ar- 
mature or the fields. 

791. Upon what principle does the alternating current 
motor act ? 

Ans. Upon the principle of induction, having for it? 
main accessory the rotary field. 

792. How is a rotary' field produced? 



1136 Steam Engineering 

Ans. By the use of polyphase currents. ^ 

793. Explain the meaning of the term rotary field. 

Ans. In a rotary field the rotary action is purely elec- 
trical, the poles simply rotating around the circle. There 
is no rotation of the mechanism of the field. 

794. What then is a revolving field ? 

An^. A field that revolves around an axis like a wheel. 



Electric Currents 

Eeferenee having been frequently made in the foregoing 
pages to different kinds of electric currents^ such as direct, 
alternating^ two and three phase^ etc.^, it is now in order to 
give a short explanation of their leading characteristics. 
The direct current is in a measure explained by its title 
direct, meaning that it travels in the same pressure direc- 
tion straight from the generator to the locality where it 
does work, and then back again to the generator, over the 
return wire. The natural tendency of the current gener- 
ated in all dynamos is to alternate, that is it starts at a 
value of zero, rises to a maximum of one polarity, de- 
scends to a value of zero again, and changing in direction 
of pressure, attains a maximum of opposite polarity, from 
whence it returns to zero again, these alternations being 
constantly repeated over and over again. In the direct 
current generator the alternating electro-motive force pro- 
ducing this current is reversed or commuted at the proper 
Instant by means of the commutator, and brushes, and the 
result is that a one direction electro-motive force, having a 
constant fixed potential or voltage, is impressed upon the 
■external circuit. 

The alternating current. In order to get a clear concep- 
ition of the true nature of the alternating current it is ab- 
solutely necessary that the student should comprehend, and 
bear in mind the meaning of the different terms used in 
alternating current practice, such as volts, amperes, fre- 
quency, phase, and power-factor. These will be taken up 
and discussed in their logical order, with reference to their 

1137 



1138 



Steam Engineering 



practical meanings omitting as much as possible all theo- 
retical^ and mathematical deductions. The voltage^ or 
pressure in an alternating current does not have a constant 
fixed value, as in the direct current system;, but is contin- 
ually changing in amount, and alternating in the direction 
of pressure at equal, regular intervals of time. Eeference 
to Fig. 496 will serve to explain the action of the alternat- 
ing electro-motive force within the generator, and also the 
action of the alternating current producedby it. The hori- 
zontal line having degrees from to 360 marked upon it 
represents the line of zero values or no voltage. The lengths 




270^ 



Fig. 496 

SINE CURVE OF GENERATING CIRCLE. 

of the vertical lines correspond to the distance of points of 
the curve -from the horizontal or zero line. The left hand 
quadrant of the generating circle is divided into angles of 
22 V2^ or one sixteenth of a circumference. For each angle 
lines are drawn, such as M P. On the zero line, divisions 
corresponding to the angles are laid off, and ordinates 
erected upon them. Each sine determines the length of the 
ordinate corresponding to its angle, as for instance the sine 
M P of 45° determines the length of the ordinate M P 
erected on the second (or 45°) of the sixteen divisions of 
the zero line. 



k 



Electric Currents 1139 

The sines as drawn in Fig. 496 represent the values of 
the E M F from zero to 90° or one- quarter of the gener- 
ating circle, and the length of the ordinate erected upon 
the 90° point of the zero line corresponds to the highest 
voltage value of the current wave above the zero line. The 
portion of the wave above the line may be assumed to rep- 
resent the positive pole, and the portion below the line the 
negative pole. 

It will easily be seen that if sines are drawn in each 
quadrant of the circle, the lengths of the ordinates for the 
remaining parts of the. wave curve may be determined from 
them, and thus a true representation of one complete wave, 
or cycle, be obtained. 

In the alternating current dynamo the current is sent to 
the line exactly as it is generated in the armature, flowing 
out one wire, and back on the other and then reversing, and 
flowing out on the wire on which it has just flowed in, and 
back on the wire on which it had formerly flowed out. An 
illustration which will more fully explain this action can 
be found by supposing the two ends of the cylinder 
of a piston pump were connected by means of a pipe 
and then, having done away with all the valves except 
the suction valves, the pump was started. At the be- 
ginning of the stroke, water would be forced out one 
side of the cylinder around the pipe into the other 
side of the cylinder, and after the piston had reached 
the end of the stroke and started back, the water 
VN^ould then take a return course back to where it had 
started. In this case the pump could be likened to the dy- 
namo, and the pipe to the wires, and the current to the 
water flowing back and forth. As the water pressure in the 
pipe will fluctuate, reaching maximum at one point in the 
stroke, and zero at another point, so also when the alter- 



1140 



Steam Engineering 



Hating current wave reaches its point of highest voltage or 
pressure the whole circuit is affected, and when it reaches 
zero value, the whole circuit is at zero. The expression wave 
should be clearly understood. It means that the whole cir- 
cuit passes simultaneously through the values of the cycle 
represented in the wave curve. The number of waves per 
second is called the frequency of the current, therefore' 
when we speak of a frequency of 60 we mean that it re- 
quires one-sixtieth of a second for the voltage to pass 
through a complete cycle, or in other words 60 cycles are 









^. 










B, 


c 




£. 














♦-- 




""■^^ 




















^ 




>^ 








o 




>. 








CL 




\ 








A 


B 


C 


\ ^ 


/ 


E 


Uj 








/ 




:ik 








X 
















K. 








>^ 




^ 








— ^ 




o 












U4 












^ 






^ 1 


Fig. 497 |l 


c 


GRANGES IN 


AMOUNT AN 


D DIRECTION 


OF PRESSUR 
-ia iG moQ-nf 


^ 1 



the change in direction of pressure, or voltage, of the cur- 
rent, and it will be seen by reference to Fig. 497 that two 
alternations occur in each complete cycle, one at C, and 
the ot})er at E, (assuming that we start at zero value of A). 
Alternations are usually expressed in terms of the number 
per minute, as for instance 7,200 alternations means 60 
cycles per second; for since there are two alternations per 
cycle, the number of cycles per minute will be 7,200-=-2= 
3,600, and the cycles per second, or frequency will be 



Electric Currents 1141 

3^600-^60=60. The following table gives the alternations 
corresponding to the usual commercial frequencies : 

Frequency. Alternations. 

25 3,000 

50 6,000 

60 7,200 

133 16,000 

The action of the alternating current as represented in 
Figs. 496-497 can be considered as continuing indef- 
initely in the same regular order, and in the same inter- 
vals of time. Eeferring to Fig. 497, the curved line AB', 
CD' E represents the alternating voltage as it rises at A to 
a positive maximum value at B', then falls to zero at Cj, 
where the direction of pressure is reversed, and the same 
maximum value of the voltage in the negative direction is 
reached at D' when it again falls to zero at E. The word 
^^period^^ is sometimes used to designate the time in seconds 
or fractions of a second required to pass through a complete 
cycle, and the number of periods per second is termed the 
frequency. We have so far considered only the voltage wave 
but in actual practice the volt-meter does not indicate the 
peak of the voltage wave, but rather that of the current 
wave, which is usually about 0.707 or roughly speaking .7 
of the maximum voltage. For instance, when the volt-meter 
reading is 110 volts, the maximum value at the peak of the 
wave will be 155 volts, nearly. The pressure indicated by 
the volt-meter is the effective voltage, and it is with this 
voltage value that the engineer is concerned in every-day 
work. 

The maximum voltage is important to the station man 
only in testing insulating materials, and in the design of 
line insulators on high tension transmission lines. As in 



1142 



Steam Engineering 



the case of the volt-meter^ the ordinary alternating amme- 
ter measures about 70.7 per cent of the maximum value of 
the amperes at the peak of the current wave. The amme- 
ter reading of effective current produces the same heating 
effect, gives out the same available energy as a direct cur- 
rent of the same amount. When there is no apparatus with 
an iron magnetic circuit connected to an alternating cur- 
rent system, such as induction motors, arc lamps, etc., the 
current wave will begin to rise with the voltage wave, reach 
its maximum value at the same instant as the voltage does^ 




Fig. 498 
voltage and current waves 

and complete the cycle in exact time relation with the | 
voltage. Fig. 498 shows both the voltage and the current 
waves, the zero line being divided into 360° as in Fig. 496. 
The full line represents the voltage wave, and the dotted 
line the current wave. In commercial alternating current 
work the choking action or "inductance^^ as it is called 
which results from the presence of the iron magnetic cir- 
cuit, caused by the connection of the electrical apparatus 
with the main circuit, and in which apparatus there is more 
or less iron surrounded by, or enclosing coils, causes the 



Electric Currents 



1143 



current wave to lag behind the voltage wave^ that is the 
zero/ maximum^ and all intermediate values of the current 
v^^ill follow a certain interval of time^ or a certain number 
of electrical degrees^ behind the corresponding values of the 
voltage. 

Phase, Lag, and Lead. — The term phase is employed to 
denote the relative posHion of a current wave with respect 
to the wave of electro-motive force producing it. Fig. 498 
shows voltage and current in phase^ that is the waves of 







, 


X. 


, 








1 


\ 


\ 


270" 


360'' 





45^^90" 


/ao° 


\ 




- T' 

/ 
/ 






*■- 




\ 




/ 


> 


^5^ 


< 




\ 


''v, / ,'' 


/ 


ANGLE 


\ 








or 






^^ 







LAG 

Fig. 499 
current lagging 45 degrees behind the voltage 



both are in unison^ both starting at zero^ and reaching their 
maximum values at the same instant. If however the cur- 
rent lags behind the voltage^ as shown by Pig. 499, it is 
said to be out of phase^ and the amount of this lag in de- 
grees is called the angle of lag, and depends upon the na- 
ture of the load^ being greatest for a load of induction mo- 
tors, and series arc lamp. 

In Fig. 499 the current wave (dotted line) is shown as 
lagging 45 electrical degrees behind the voltage wave (full 
line), and in this case the angle of lag is 45°. 






1144 



Steam Engineering 



In some cases, especially in the operation of rotary con- 
verter^, and synchronous motprs, the current wave may be 
ahead of, or lead the voltage wave. This is caused by an 
action directly the opposite of inductance, called capacity, 
and is illustrated in Fig. 500, where a current lead of 15 
electrical degrees is shown, and in which the angle of lead 
is 15°. In the alternating current-generator the field coils 
occupy about 50% of the surface of the field bore, because 
when their inner edges are tight together, their outer edges 
are apart, due to the larger circumference at the pole pieces, 




360" 



— /5 
ANGU 

or 

lCAD 

Fig. 500 

showing a current lead of 15 degrees 

and because some interpolar space must be left to prevent 
excessive leakage from pole to pole. 

Only 50% of the armature bore is wound, for otherwise 
the coils would be so wide that they would extend over into 
the field of a wrong pole piece. If one side of a coil is un- 
der a N-pole the other side should be under a S-pole. Then 
the two electro-motive forces induced, add together. 
Should the coil be so wide as to extend over to the next 
N-pole any electro-motive force induced by that pole would 
be subtracted. 



Electric Currents 1145 

There is then on the ordinary alternator half of the ar- 
mature empty. Such a machine is called a Single Phase 
Alternator. 

Two and Three Phase, — It occurred to some inventor 
that an entirely separate winding could be put on between 
the coils of the original windings, and be connected to its 
own collector. The current was to be led to a different cir- 
cuit, but it soon became evident that it was better to make 
of the four wires from the alternator, a three-wire circuit 
by joining two of them inside the armature and leading out 
three wires to the switchboard. Such an alternator is a 
Two Phase Alternator. 




Fig. 501 

3-PHASE y CONNECTION 

Of course the capacity of the machine is not doubled, be- 
cause from a single phase alternator is drawn enough cur- 
rent to heat it to the safe limit. From a two phase alter- 
nator we do the same thing. The reason we gain in capac- 
ity is because in a single phase machine the heating is con- 
centrated, while in the two phase machine it is evenly dis- 
tributed all over the armature. 

Even in a two phase alternator there is a portion of the 
armature not used for winding, and there was still a desire 
to reduce the number of line wires. This led to the Three 
Phase Alternator. 



1146 



Steam Engineering 



The three armature windings of the alternator are con- 
nected together at one pointy and the other ends to the 
three collector rings, or the three windings are connected 
in series and the three points where they are joined are 
connected to the three collector rings. 

The former winding is called a Y winding and is shown in 
Fig. 501. The latter is a A (Delta) winding and is shown in 
Fig. 502. The European names are respectively Star and 
Mesh windings.- 





Fig. 502 
3-phase delta connection 



The three wires of a three phase system each act as a 
main wire, and a return wire for one of the others at the 
same time. The actual current in the wire is the difference 
of the two currents : in and outgoing. 

If the same three phase armature is connected first as a 
Y and then as a A winding these differences will be noticed. 

The Y armature will give the higher voltage and have 
less current capacity. The A will give a lower voltage and 
have greater current capacity. Power that can be drawn 
from each is the same. 

Transformers and other apparatus are wound two, and 
.three phase, and also Y and A, for use with the correspond- 
ingly wound alternator. 



Electric Currents 



1147 



By a peculiar connection of coils^ rotary converters are 
wound for six phase currents; it having been discovered 
that it is possible to do m) with the result of increased out- 
put for a given sized machine. 




Fig. 503 
waves in quadratuee 



Two^ three and six phase machinery is often grouped 
under name of polyphase. 

Waves in quadrature. — Fig. 498 shows waves in phase. 
In Fig. 503 are shown waves in quadrature, that is the 





Fig. 504 
waves in opposition 



Wangle of lead is 90° which is a quarter of a circle. When 
the angle of lag, or lead is 180° the waves are said to be in 
apposition. This is illustrated in Fig. 504. 



1148 Steam Engineering 

QUESTIONS AND ANSWERS. 

795. What is the leading characteristic of the direct 
current ? 

Ans, It travels in the same direction of pressure. 

796. What is the tendency of the current generated in 
all dynamos? 

Ans. It is alternating in voltage or pressure. 

797. Explain the meaning of the term alternating as 
used in this connection. 

Ans. The current starts at a value of zero, rises to a 
maximum of polarity, descends to a value of zero again, and 
changing in direction of pressure, rises to a maximum of 
opposite polarity, from whence it drops to zero again. 

798. How then is direct current produced from this al- 
ternating current? 

Ans, By means of the commutator and brushes on the 
direct current generator. * 

799. What is the leading characteristic of the alternat- 
ing current? 

Ans, Its voltage is continually changing at regular in- 
tervals from zero to maximum in the direction of opposite 
polarity. 

800. How is this action best represented? 

Ans. By wave curves drawn above and below a horizon- 
tal line representing zero. 

801. In what manner does the action of the alternating 
current affect the circuit through which it travels ? 

Ans. The whole circuit passes simultaneously through 
voltage values of the cycle represented by the wave curve. 

802. What is meant by the frequency of an alternating 
current? 

4ns. The number of waves or cycles per second. 



Questions and Answers 1149 

803. What does a frequency of 60 mean? 

Ans. It means that the voltage values pass through a 
complete cycle in one sixtieth of a second^ that is 60 cycles 
per second. 

804. What is meant by alternations? 

Ans, The number of reversals per minute in the di- 
rection of pressure. 

805. How many alternations would there be in a cur- 
rent having a frequency of 60 ? 

Ans, 7,200. 

806. What is meant by a ^^period?^^ 

Ans. The time in seconds or fractions of a second re- 
quired to pass through a complete cycle. 

807. What is meant by current wave? 

Ans. It means the actual values of the current as shown 
by the volt-meter and ammeter. 

808. Do these equal the values of the theoretical wave 
curve ? 

Ans, They do not, reaching about 70 per cent. 

809. Why is this? 

Ans, It is due to the influence of the iron magnetic 
circuit caused by the connections of induction motors, arc 
lamps, and other electrical apparatus. 

810. What is meant by effective current? 

Ans, The voltage and volume as shown by the volt- 
meter and ammeter. 

811. In what respect is the maximum voltage as shown 
by the calculated wave curve useful? 

Ans, It is useful in testing insulating materials. 

812. What is meant by phase in electric practice? 
Ans. It denotes the relative position of a current wave, 

with respect to the wave of electro-motive force producing 
it. 



1150 Steam Engineering 

813. When is a current in phase? 

A71S. When the two waves just mentioned start at zero 
and reach their maximum values at the same instant. 

814. What is meant by lag? 

Ans. When the current wave lags behind the voltage 
wave. 

815. What is meant by lead? 

Ans. When the current wave is ahead of^ or leads the 
voltage wave. 

816. What is the meaning of two and three phase cur- 
rents ? 

Ans. When the winding of the armature is such that 
two or three electro-motive forces in quadrature with each 
other are simultaneously produced by the generator the cur- 
rents thus produced may be distributed over four or six 
conductors^ a pair for each current. 

817. Is it necessary to have a pair of conductors for 
each current in two and three phase current work? 

Ans. No. By means of the Y winding it is possible to 
distribute the current over three wires^ each wire acting as 
a main^ and return wire for one of the others. 



Armature Design and Construction* 

Economy of construction demands that an armature be 
run at a high rate of speed. In any armature the output in 
volts can be increased by simply increasing the speed; the 
output in amperes cannot be so increased unless at the same 
time larger wires are used. If^ however^ in any armature 
we should increase the size of the wires^ so that fewer turns 
would be upon it^ we can compensate for the consequent 
loss in voltage by increasing the speedy and thuSj with the 




Fig. 505 



same armature, also increase the output in amperes. It will 
be seen that speed is an important item in the construction 
of any armature. To operate at a high rate of speed re- 
quires the very best workmanship and mechanical construc- 
tion. 

Whenever a high speed is to be used it is of the utmost 
importance to see that the armature is well balanced. Any 



*From ^^ Armatures and Armature Winding," by Horst- 
man and Tousley.- — 

1151 



1152 



Steam Engineering 



rotating piece of machinery is said to be out of balance 
when one side is heavier than the other. This condition of 
being out of balance will manifest itself by a more or less 
severe jarring^ and shaking of the frame upon which it 
rests when running. 

Whether an armature is in balance while at rest can be 
easily determined by placing it upon two knife edges, as 
shown in Fig. 505. If these edges are perfectly level, 
the armature will roll to one side or the other until the 
heavier part is at the bottom. If the diameter of the ar- 
mature is small compared to its length, this test will not 
be very sensitive. If the diameter is great as compared to 




Fig. 506 



its length a small excess of weight on one side will cause it 
to roll over. If a very good balance for high speed is to be 
obtained this method must not be relied upon. In such a 
case the armature should, be placed in bearings and run at 
its proper speed. If there is much jarring or shaking the 
armature is out of balance, and this must be rectified. 

It is obvious that this had best be done before any wire is 
placed on the core. How it may come about that the arma- 
ture may be perfectly balanced statically and yet almost 
u^fit for the work while in operation at a high rate of speed 
can be seen from Fig. 506. If there is an excess of 
weight at 1 this may be perfectly balanced for a state @f 
rest by the addition of a similar weight at 2. If, however. 



Armature Construction 1153 

the armature is revolved at a high rate of speed there will 
be a tendency to strain the shaft as indicated by the dotted 
lines. 

An armature out of balance is rectified by adding weights 
at different places until the proper amount is found. This 
will make itself evident by the smooth running. If possi- 
ble, the weights should now be removed and an equal weight 
of metal removed from the armature at the side opposite 
to that at which it was found necessary to add weight. If. 
for instance, it was found necessary to add one pound at 
3, Fig. 506, the same result can be obtained by removing 
one pound at 1. 

In speaking of high speeds is must be understood that it 
is not, necessarily, a great number of revolutions that are 
required to produce a certain E. M. F. What is required 
is that a certain number of conductors shall cut through 
the lines of force passing between the pole-pieces in a given 
length of time. As these conductors are always located on 
the periphery of the armature, it is the speed of this part 
that counts. The greater the diameter of the armature, 
therefore, the lower the speed of the shaft. Other things 
being equal, the capacity of an armature is directly propor- 
tional to its length. We may therefore choose whether we 
shall increase the capacity of a machine by increasing the 
length of the armature, or the diameter. 

If the length of the armature is too great there is some 
danger that the shaft will bend, not only from centrifugal 
force to which it is subject, but also from the magnetic at- 
traction of the pole pieces if it is not well centered. 

The centering of an armature is an important point. 
It rests between two powerful lyiagnets. If it is exactly in 
the center, the attraction of one pole piece will neutralize 
that of the other ; but if it is the least bit out of center, there 



1154 Steam 'Engineering 

will be a strong attraction to one side and this will greatly 
add to the friction. The bearings and pole pieces should 
be in such relations to each other that they can be truly 
centered^ and that there will be no likelihood of their 
becoming loosened- The bearings should have sufficient 
surface so that the wear will be a minimum. Bearings 
should^ furthermore^ not be of iron or steel. If the 
shaft is constructed of the same material there may 
be some magnetic attraction between the shaft and the 
bearing which would increase the friction, and cause 
heating. Bearings should also be out of line of the 
magnetic circuit, as such magnetization will cause the 
shaft to generate Foucault currents, which will heat it, and 
in turn heat the bearings. The shaft should also be pro- 
tected by shields, which will prevent oil from running along 
it and getting into the wires on the armature. The lateral 
play which is essential to the smooth running of the shaft 
can be obtained by lining up the shaft after the belt is put 
on. This lateral play also tends to distribute the wearing 
surface of the brushes over the surface of the commutator, 
thereby giving a more uniform contact surface. It is quite 
evident that if the armature was made to run without this 
lateral movement the brushes would always bear on the 
same part of the commutator and a ridge would soon ap- 
pear on it. 

The inexperienced mechanic should be warned not to 
skip lightly over any part of the work. While, of course, 
there is no visible connection between the armature and 
the pole pieces of the machine, and while it seems to be 
turning free and easy, it must be borne in mind that the 
force exerted upon the armature is, nevertheless, just as 
great as though a friction clutch of the capacity of the ar- 
mature were applied to the periphery of the armature. 



Armature Construction 1155 

Furthermore^ in the case of a sudden overload, or short 
circnit, or too rapid starting in the case of a motor, the 
force applied is almost as severe as the blov^ of a hammer. 

MECHANICAL CONSTRUCTION OF THE ARMATURE. 

All good armatures are made up .of a number of punch- 
ings similar to those shown in Figs. 507-508-509. These 
punchings are made of soft iron or steel. The figures 
illustrate the different forms of slots used in connection 
with armatures. Into these slots the wires are wound, as 
will be hereafter explained. The punchings are usually 
made of thin iron with some form of insulation provided 




Fig. 507 Fig. 508 Fig. 509 



between them to reduce the Foucault, or eddy, currents. 
This insulation is obtained by inserting layers of thin paper 
between the sheets of metal, or by coating the punchings 
themselves. Paper, and similar materials used for this 
purpose w411 in time char from the heat of the armature 
and work out and tend to loosen the armature. Care 
should also be exercised in the use of an insulating var- 
nish, as some of these varnishes soften from the heat of the 
armature, and are thrown out on tlie pole pieces. 

As many of the punchings as are necessary are slipped 
upon the shaft of the armature as indicated in Fig. 505, 
and fastened together with clamps shrunk upon the shaft. 



1156 Steam Engineering 

or with large nuts screwed on the shaft. Bolts extending 
through the punchings are often used. These bolts must 
be insulated from the punchings; otherwise there will be 
a flow of current through the shafts the body of the arma- 
ture and the bolts. It is well to remember in la3dng out 
the armature and the means of fastening it to the shaft 
that the Foucault currents will flow according to the prin- 
ciples of any other electrical circuity so that to keep these 




Fig. 510 

currents to a minimum, no electrical paths should be pro- 
vided through the armature core. 

Where an armature is slotted as indicated in Fig. 505, 
some of the punchings are often made of smaller diameter 
than the rest, or are afterward turned down as indicated in 
the figure. This is to allow room for the binding wires 
which are put on after the winding is completed. Some- 
times the punchings are not slotted, but are milled out, 
and narrow bars of metal or wood inserted in the grooves 
as shown in Fig. 510. These bars are for the purpose of 



Armature Construction 1157 

keeping the wires from slipping. ^ If of metal^ they must 
be insulated from the punchings for the same reason as was 
explained with the use of bolts. 

In some cases the slots are made partially closed as 
shown. This makes it a little more difficult to insert the 
wires^ but they are then held securely in place. Often 
these slots are made wedge shape^ and the tops closed by 
means of wood or fiber strips after the wires have been 
put in place. In some cases the slots containing the wires 
are entirely closed. 




Fig. 511 



In slotted armatures^ especially if the slots are deep^ 
when the punchings are forced together, that part of the 
punchings which projects beyond the ring E, Fig. 505, is 
likely to bulge out. In order to prevent this a few pieces 
of extra heavy metal are obtained and used at the ends. 
One punching of insulating material is also generally used 
at each end. 

For small armatures the punchings are generally left 
solid. With diameters of 18 inches or so, openings are left. 
These openings lighten the armature, and are also useful 



1158 Steam Engineering 

in ventilating it to reduce the heating. With very large 
armatures^ opportunities for radial ventilation must also 
be given. For this purpose some of the punchings are 
corrugated^ or otherwise arranged^ so that they allow aii 
to pass from the center outward. When such pieces (see 
Fig. 511) are used in connection with the openings shown 
in the punchings^ the air drawn in at the sides escapes ra- 
dially^ and thus helps to keep the armature cool. 

The punchings are preferably made of metal ranging 
from 10 to 30 mils in thickness. The thinner the better, 
so long as the metal can be easily handled. Punchings 
should be made as accurate as possible. Where it is nec- 
essary to turn down an armature to obtain perfect round- 
ness^ the Foucault current losses are greatly increased. 
This is due to the fact that the cutting tool of a lathe has a 
tendency to bend over the edges of the thin punchings^ and 
cause an electrical contact which allows current to flow. If 
it is necessary to smooth down an armature this work is 
best done with a sharp file. 

ARMATURE V^IIS^DII^G. 

Armature windings are divided into three general 
classes, viz. : 

1 — Eing wound armatures. 

2 — Drum wound armatures. 

3 — Disk wound armatures. 

The winding of each of these classes is again subdivided 
into what is known as open coil winding, where the wind- 
ing is part of the time on open circuit; and closed coil 
winding, where the winding forms a closed circuit. 

The ring and drum windins^s are in most general use, 
the disk winding not having had any extensive applica- 



Armature Winding 



1159 



tion in this country. On direct current machines^ wind- 
ings of the closed coil type are generally used;, although 
the open coil type of armature is employed on some con- 
stant current arc light generators. This type of armature 
is open to the serious objection that the sparking at the 
brushes is excessive^ and some special means must always 
be provided to reduce it. 

Gramme Ring. — The ring wound armature^ or as it is 
more commonly called, the Gramme ring armature, com- 
prises an iron core made in the form of a ring around which 
are wound the conductors which are*to convey the current. 




Fig. 512 



The various coils are wound on separately, the wire being 
carried over the outside of the iron core, then through the 
center opening and again around the outside of the core, 
this operation being repeated until all the wire for that 
individual section is wound on. The adjacent coil is then 
wound on in the same manner, the ends of each coil being 
brought out to the commutator side of the armature. 

There are various advantages, and disadvantages, to this 
class of winding and, the conditions under wiiich the ma- 
chine is to be used must be taken into consideration in de- 
termining whether it is the best form to use. 



1160 



Steam Engineering 



As only those conductors which cut lines of force are 
active in the production of current^ it is evident that those 
conductors which lie on the inner side of the iron ring serve 
no useful purpose so far as the generation of current is con- 
cerned. Numerous attempts have been made to utilize this 
part of the winding by making the pole pieces extend around 
the ring in such a manner that lines of force will pass to 
the inside of the ring ; also by arranging an additional pole 
piece on the inside of the armature but mechanical consid- 
erations have shown these methods to be impractical. 




Fig. 513 



The dead wire on the inside of the armature constitutes 
one of the greatest disadvantages of this class of windings 
and this is especially the case where the armature carries 
heavy currents. In arc lighting machines^ where a compara- 
tively small current is used^ this loss is not of so great im- 
portance^ and is entirely outweighed by the several advan- 
tages^ as will appear after further consideration. In laying 
out ring armatures it is well to remember, that, where the 
armature coils consist of only a few turns of fairly heavy 
conductor, the losses become proportionately less as com- 



Armature Winding 



1161 



pared with the drum armature^ as the cross connectors on 
drum armatures also form an inactive part of the circuit. 

In Fig. 514 is shown a simple ring wound armature with 
a bi-polar field. The end of one coil is connected to the 
beginning of the next^ and the winding therefore forms a 
continuous spi-ral^, encircling the iron ring core. Taps taken 
off at the point of connection of the various coils are carried 
to segments of the commutator^ brushes being provided, to 
either conduct the current from, or convey it to the commu- 




Fig. 514 



tator as the case may be. It will be seen that with an arma- 
ture of this kind each individual coil is generating an electro- 
motive force which is proportional to the number of lines of 
force being cut by the coil. Assuming for the present that 
we have a uniform field, it is plain that the volt-meter con- 
nected across the ends of coil 13, or 5 would indicate a certain 
difference of potential, and the potential readings over the 
other coils would show a gradually diminishing difference of 
potential, until we reach the point of brush contact, where 



1162 Steam Engineering 

the difference of potential would be practically nothing. It 
is also evident that at no place in the winding is there any 
great difference of potential between adjacent wires, or be- 
tween adjacent commutator segments. By greatly increas- 
ing the number of coils and^ also the number of commutator 
segments^ the difference of potential between adjacent coils 
and commutator segments can be still further reduced. 

A further inspection of the drawing will show that there 
are no crosses between wires of opposite polarity on the taps 
extending to the commutator segments. Herein lies one of 
the great advantages of this style of winding over the drum 
winding. 

Other advantages pertaining to this class of winding are 
as follows: 

(a) As it is possible to increase the diameter of the arma- 
ture without greatly increasing its weighty a much higher 
velocity can be obtained in the moving conductor, with a 
corresponding increase in the induced E. M. F. 

(b) A defective coil can be easily detected, and easily re- 
placed without disturbing the balance of the winding. 

(c) In case of emergency a defective coil can sometimes 
be cut out, and the machine still operated. 

(d) Better ventilation due to the open style of construc- 
tion. 

Its disadvantages in addition to those already mentioned 
are : 

(a) The resistance of the magnetic circuit is increased, 
owing to the shape of the armature. 

(b) A ring armature requires more work in the winding 
as each coil has to be wound by hand, and is therefore more 
expensive. 

While ring armatures are all wound in practically the 
same manner, i. e., each coil wound separately, a number of 



Armature Winding 



1163 



different connections between the coils^ and the commutator 
segments are employed. A development of the faces of the 
pole pieces^ together with the armature conductors^ will 
show in a plainer manner the relations existing between the 
coils and their connections. The development of the arma- 
ture in Fig. 514 is shown in Fig. 515^ and is that view which 
would be obtained were a person to take a position corre- 
sponding to that occupied by the armature shaft and make 
a complete revolution^ thus bringing into view consecutively 
all the pole piece faces^ and the armature conductors. 



mmmBEEHEEHmsmEHp 





"^ Kj Kj 



Fig. 515 



In the figure the full lines denote the active conductors^ 
and the dotted lines the inactive conductors on the inside 
of the armature ring. The small squares at the top repre- 
sent the commutator segments, and the shaded cross sections 
the pole pieces. The arrows indicate the direction of flow 
of the induced current. 

By an examination of the figure it will be seen tliat there 
are two commutator segments, one at which tlie current in 
both wires connected to it has a tendency to flow in a posi- 
tive direction, or toward it, and the other where tlie current 
tends to flow away from it, or in a negative direction. These 
are obviously xhe proper locations for the brushes. It will 



1164 Steam Engineering 

be seen further that the end of one coil connects to the be- 
ginning of the coil next to it. 

While the figure represents a simple armature of sixteen 
coils, it is apparent that the number of coils could be greatly 
increased or, instead of a coil having but one turn, it could 
consist of a number of turns of wire. 

Drum Windings. — The drum wound armature varies pri- 
marily from the ring wound armature in the shape of ^"he 
core. While with the latter the core is in the shape of a ring 
or hollow cylinder, the conductors being wound spirally ^ 
around the ring, with a drum-wound armature the core i& 
in the shape of a solid cylinder, or drum, the conductors 
being wound around the outside surface in a direction par- 
allel to the shaft. It must not be understood that the shape 
of the core alone determines the class of armature winding, 
for in some machines a drum winding is placed on a ring 
core. The distinguishing characteristic of the ring wind- 
ing is, that the active conductors, which pass over the face 
of the armature from the front to the back, have their re- 
turn conductor pass through the opening in the center of 
the ring from the back to the front, this part of the con- 
ductor being inactive in the production of current. With a 
drum winding the conductors, in returning from the back 
to the front of the armature, also pass over the face of the 
armature, where they can cut lines of force and are also 
active in the production of current. It will thus be seen that 
in the ring armature considerable of the wire is not only 
inactive in the production of current, but at the same time 
is the cause of a loss of energy, due to its resistance, with 
a resultant heating of the armature. This objectionable fea- 
ture is to a great extent overcome in the drum winding. 
Less wire therefore has to be used on a drum-wound arma- 



Armature Winding 



1165 



ture^ other conditions being equal^ than on a ring-wound 
armature of the same capacity, and the armature has a 
lower resistance. 

At first glance the winding of a drum armature appears 
a quite difficult matter, but with a little study it will be 
found that it is not very much unlike that of the ring arma- 




Fig. 516 



ture. A simple case of drum winding is shown in Pig. 516. 
There are 12 conductors on the armature face, and 6 com- 
mutator segments. Suppose we take a wire and connect it 
I to segment a of the commutator. Now start to wind around 
the armature, passing along 1 to the rear and returning by 
way of 6 to the front where we loop back to commutator seg- 



1166 Steam Engineering 

ment &. Now make another turn around the armature by 
way of 3 and 8^ returning to segment c of the commutator. 
Repeat this procedure^ gradually turning the armature to 
the left. When the last turn ll^, 4 has been made^ we come 
back to commutator bar a, the one from which we started. 
This operation can be considered as simply winding a wire 
spirally around the drum^ and bringing down loops to the 
commutator segments^ ending at the point from which we 
start. 

The first question which presents itself to the student is^ 
Why does not the wire which passes over 1 return in the 
diametrically opposite position^ or 7 ? Consider for a mo- 
ment the armature shown in Fig. 516. Suppose we start 
our wire at segment a of the commutator^ pass to the rear 
of the armature along 1, and return to the front end along 
the diametrically opposite position 7. Now loop back to 
segment h of the commutator and from there make another 
turn around the armature by way of 3 and 9 and back to 
segment c. Prom segment c make another loop around the 
armature by way of 5 and 11 and return to segment d. It 
will now be seen that we have made a complete revolution 
Df the armature^ but have made connection to only half the 
commutator segments. In order to keep up the winding in 
a regular manner, the wire from commutator segment d 
should pass to the rear of the armature along space 7, but 
this space we find already occupied by the return of 1. If 
we were to continue with our winding from this point, we 
would have to carry the wire from segment d to position 6 
or 8, but this would result in an unbalanced winding. 

It is plain that, in order to keep the winding symmetrical, 
the conductors in passing from the front to the rear of 
the armature must occupy the positions 1, 3, 5, 7, 9, 11, and 



Armature Winding 



1167 



the even numbered positions will then serve as the returns 
for these wires. 

It will be noticed that in the example shown there are 
6 coils^ comprising 12 conductors and 6 commutator seg- 
ments. If the armature was so designed that we had an 
uneven number of coils^ for instance 7 coils^ in which case 
there would be 14 conductors^ and 7 commutator segments^ 
the rear connections could be made directly across a diameter 
as shown in Fig. 517. This gives a perfectly symmetrical 




Fig. 517 



winding. Only one coil will be short-circuited at a time 
f or^ with the brushes set across a diameter of the commuta- 
tor when one brush is in such a position that it laps across 
two segments^ the other brush is in the center of a segment. 
Fig. 518 shows the connections of a drum-wound arma- 
ture having 8 coils comprising 16 conductors and 8 commu- 
tator segments. While in the example shown each coil con- 
sists of only a single loop with two conductors^ a coil may 
consist of a number of turns of wire, in which case the 



1168 



Steam 'Engineering 



drawing indicates merely the connections for the beginning 
and end of each coil. 

As has been previously explained, the conductor which 
passes from the front to the rear of the armature along space 
1 cannot be brought back to the front of the armature if 
the winding is to be perfectly regular along the diametri- 
cally opposite space, 9, but must return along one of the 




" Fig. 518 

spaces to the right or left of 9. The expression for deter- 
mining the proper spacing for the return conductor is: 



i(^-\ 



where y=spacing or pitch, 

n==number of poles, 

z=number of conductors, 

bi=number of conductors to a coil. 
The symbol + means simply, plus or minus, that it is op- 
tional with us whether we add 1 to, or subtract 1 from the 
number found by the operations indicated in the formula. 



Armature Winding 1169 



In Fig. 518 n=:i2, z=16, b=2, therefore 
2 



-("-) 



_ =7. 
2 

Each conductor is connected at the rear of the arma- 
ture to one 7 spaces in advance of it ; as 1 to 8, 3 to 10, 
etc. 

In winding an armature according to the plan shown 
where each coil consists of a number of turns of wire, we 
would start with the wire connected to commutator segment 
a, and wind along space 1 to the back of the armature^ thence 
across the back of the armature to space 8, returning to the 
front of the armature along space 8 and across the front to 
space 1, continuing until all the wire of this coil is wound 
on. The end of the wire would now be brought to segment 
h of the commutator. The second coil is now wound on, 
starting from segment h and winding to the back of the ar- 
mature along space 3, across the back to space 10^ to the 
front along space 10 and across the front to space 3, con- 
tinuing in this manner until this coil is also wound on. The 
end of this coil is now brought to commutator segment c. 
The remaining coils are wound on in the spaces indicated. 

In the actual winding of an armature the commutator is 
generally left off during the process of winding, the begin-^ 
ning and end of each coil being brought out and connected 
to the commutator after the armature is completely wound. 
A winding table which shows the several steps just de- 
scribed and which is very convenient both for winding and 
connecting is given below : 

»a-l-8-b e-9-16-f 

b-3-lO-c f-ll-2-g 

c-5-12-d g-13-4-h 

d-7-14-e h-15-6.a 



1170 



Steam Engineering 



This table shows both the position of each coil and the 
commutator connections; for instance^ segment h is con- 
nected to the end of coil 1-8 and to the beginning of coil 
3-10. 

The development of the armature winding. Fig. 519^ will 
show in a plainer manner the various connections made^ also 
the direction of flow of the induced current in the various 
conductors. Following out the direction of current it will 
be seen that at commutator segment f, the current in both 
conductors flows toward the segment, while in segment h 




Fig. 519. 

the current flows awav from the commutator. These two 
positions are the proper points for the brush contacts. 
• With the armature connected, as shown, the brushes lie 
in an almost direct line, between the pole pieces, and the 
connections on the front of the armature are symmetrical- 
It is quite evident that we could, without changing the or- 
der of the winding, turn the commutator through an angle 
of 90°, thus bringing the brushes in a line Avith the spaces^ 
between the pole pieces. The front connections would not 
then be symmetrical, one connection to each coil being short- 
ened, and the other being lengthened. The design of some- 



Armature Winding 



1171 



machines is such that locating the brushes in a line with 
the pole pieces brings them in an inaccessible position, and 
the commutator is therefore shifted as described. 

There are two circuits through the armature from brush 
to brush and in the position shown these circuits are as 
follows : 

b-3-10-c-5-12-d-7-14-e-9-16-f 



b-8-l-a-6.15-h-4-13-g-2-ll-f 



+ 




Fig. 520 

As the armature revolves in the direction shown by the 
arrows, the positive brush will short-circuit commutator seg- 
ments e, and f, and the negative brush segments a, and b. 
The two coils e-9-16-f and b-8-l-a will therefore be short- 
circuited, and the full difference of potential of the machine 
svill exist between them. As these coils are adjacent with 
3ach other, in a smooth face armature where the coils con- 
sist of a number of turns of wire, they will be placed side 
by side, and the question of insulation between them there- 
fore becomes of considerable importance. 



1172 



Steam Engineering 



Following out the paths on the development of the wind- 
ing, it will also be seen that there are numerous crosses be- 
tween wires of greatly different potentials. Compare with 
the ring armature winding shown in Fig. 514. 




Fig. 522 



To obviate some of the objectionable features of the wind- 
ing just described, the m.ethod shown in Fig. 520 is used. 
The value of y is in this case 5, each conductor at the rear 
of the armature being connected to another conductor 5 



Armature Winding 



1173 



spaces ahead of it. The coils short-circuited by the brashes 
are now separated^ and there are fewer crosses between con- 
ductors at the ends of the armature. Tracing out the cir- 
cuits it will be seen that the current induced in some of the 
conductors is in opposition to that of the remainder of the 
circuit. This has the effect of decreasing the demagnetizing 
effect of the armature. 

The armatures which have so far been considered have 
had but one layer of wire. Fig. 522 shows an armature 




Fig. 523 

with 24 conductors and 12 commutator segments with the 
wire placed on in two layers. The development of this wind- 
ing is also shown in Fig. 523o The winding table is given 
below : 

a-l-7-b g-19-13-h 

b-2-8-c h-20-14-i 

c-3-9-d i-21-15-j 

/: . d-4-lO-e j-22-16-k 

i^ e-5-ll-f k-23-17-1 

•:; f-6-12-g 1-24-18-a 



1174 Steam Engineering 

One of the first points which will be noted is, that each 
conductor in returning from the back of the armature to 
the front passes through the diametrically opposite space; 
coil 1-7, for instance. The rear connections are not shown, 
as they would complicate the drawing. If we start to wind 
this armature from commutator segment a, winding coil 
1-7, returning to segment & and continuing our winding 
from segment h, coil 2-8, segment c, to coil 3-9, segment d 
to coil 4-10, segment e to coil 5-11 and segment / to coil 
6-12 it will be seen that we have made a complete revolution 
of the armature and have only made connection to half the 
commutator segments. We can complete the winding by 
continuing with the outer layers. It is evident that the 
outer layer of coils will have a greater resistance due to 
their increased lelhgth and will also travel at a greater speed 
than the coils of the inside layer. 

The two paths through the armature, from the positive 
to the negative brush vary between the coils in the outer 
layer, and those in the inner layer, and in one position of 
the armature one of the paths from brush to brush is through 
the coils of the inner layer exclusively, and the other path 
through the coils of the outer. This results in a constant 
Tariation between the electro-motive forces induced in the 
two halves of the armature. 

The two paths through the armature from brush to brush 
are 

b-2-8-c-3-9-d-4-10-e-5-ll-f-6-12-g-19-13-h ") 

\ + 
b-7-l-a-18-24-l-17-23-k-16-22-j-15-21-i-14-20-h j 

As the armature moves forward from the position shown, 
coil 1-7 is short-circuited by the negative brush and coil 
13-19 by the positive brush. It will thus be seen that a 



Armature Winding 



1175 



considerable difference of potential exists between the inner 
and outer layers of wire^ and they will have to be well in- 
sulated from each other. It will also be seen that no great 
difference of potential exists between adjacent coils. The 
two short-circuited coils lying as they do^ one above the 




Fig. 524 



other, are both in the neutral point of the field at the point 
of commutation. This can be considered as an advantage 
over the previous type where the short-circuited coils are 
somewhat separated, and are therefore not commutated at 
the exact neutral point. ^ 



1176 



Steam Engineering 



In the previous examples of drum windings we have con- 
sidered only the methods of winding used with bi-polar 
fields. As has been explained elsewhere there are many con- 
ditions where the use of a bi-polar field is not advisable^ and 
numerous advantages are gained by using a multi-polar field, 
or a field consisting of more than one pair of poles. 

The same general principles apply to multi-polar wind- 
ings as apply to bi-polar windings, and these various appli- 
cations will be described. We will investigate only those 
methods in general use, there being a number of other 




^ 







Fig. 525 



schemes of winding which are in the main only extensions 
of the principles here shown. 

Fig. 524 shows an armature winding, with its develop- 
ment. Fig. 525, consisting of 18 conductors and a 4-pole 
field. Following out the circuits from one commutator seg- 
ment to the next or the developed winding, Fig. 525, it will 
be seen that the winding after making a turn of the arma- 
ture, laps back to the commutator segment next to the one 
from which it started, and is therefore called a lap winding. 
Tracing out the winding from commutator segment a, we 
find it follows the path a-l-6-b, b-3-8-c, c-5-lO-d, etc., until 



Armature Winding 1177 

it arrives at coil i-17-4-a, where it returns to the starting 
point. A complete revolution of the armature has been 
made^ and every conductor has been passed through, and 
each one only once, forming what is termed a single re- 
entrant winding. 

Observing the end connections of coil a-l-6-b, for instance, 
it will be seen that the value of y for the rear connection is 
5, each conductor at the rear of the armature connecting to 
one five spaces beyond. The value of y for the front con- 
nection is — 3, each conductor being connected to a conduc- 
tor three spaces back from it. The average spacing is there- 
fore 4, and the difference between the front and rear spacing 
is 2. 

In connecting up the armature for a bi-polar field, in 
order that the induced currents would flow in the same di- 
rection in all conductors connected in series, we found it 
necessary to connect together at the rear of the armature, 
the conductors lying under a north pole with those lying al- 
most directly opposite it under a south pole. So, in the case 
of a four-pole field, each conductor at the rear of the arma-^ 
ture is connected in series with a conductor which lies in 
a field of opposite sign which, in this case, is not across 3 
diameter, but one-fourth the distance around the armature. 
The value of y, the spacing, should therefore be nearly equal 
to the total number of conductors divided by the number oS 
poles, or z-f-n where zi=the number of conductors and n=: 
the number of poles. As explained uuder the section on 
bi-polar armatures, this spacing may be either greater or 
less than the value just given. If the spacing is greater 
than z-f-n, the cross connections will be longer, with a re- 
sulting increase in armature resistance. With the spacing 
less than z-f-n the cross connections will be correspondingly 
shortened, and the armature resistance lessened, and th« 



1178 Steam Engineering 

conductors lying between the pole pieces will then oppose 
each other. 

In Fig. 524 it will be noticed that there are an even nmn- 
ber of conductors, and that the spacing at the rear is 5 and 
at the front — 3. In all lap windings, with multi-polar 
fields, there must be an even number of conductors, and the 
spacings at the front and rear must be odd and must differ 
by 2. 




Fig. 526 

A simple plan by means of which the student may inves- 
tigate these several conditions, consists in drawing roughly 
a circle, subdividing it with as many intersections as there 
are conductors on the armature, and then drawing a series 
of connecting lines through the various points. These lines 
will then represent the armature conductors, and their con- 
nections, the lines on the outside of the circle representing 
the rear connections, and the lines on the inside of the circle 
the front connections. 



Armature Winding 



1179 



Fig. 526 shows this scheme worked out for the armature 
shown in Pig. 524. That the armature must, have an even 
number of conductors can be seen by figures similar to that 
shown in Fig. 527. Here 17 conductors are shown with a 
rear spacing of 5 and a front spacing of — 3. The line from 
13 should connect to a conductor 5 spaces beyond^ or con^ 
ductor 1, but this conductor is already connected. 




Fig. 527 

With a bi-polar fields and a one-layer winding, it will be 
! remembered that adjacent commutator segments were con- 
inected to every other conductor, the even numbered con- 
ductors being taken as returns for the odd numbered con- 
ductors. Similarly in a multi-polar armature, our spacing 
must be such that only every other conductor is connected 



'1180 Steam Engineering 

to a commutator segment. The front and rear spacings 
must therefore differ by 2. 

That the front and back spacings must be odd can be 
easily determined with the scheme previously described^ Pig. 
528 showing an armature with 18 conductors, and a spacing 
at the rear of 6 and at the front 4. We see here that the 
loops close on themselves and would form a short-circuited 
winding. 




With a lap-wound armature there are as many paths 
through the armature, and as many brushes as there are 
poles. This can be seen from the development of -Fig. 524, 
the paths through the armature being 

i-2-15-h-18-13-g 

i-17-4-a-l-6-b 

e-12-7-d-10-5-c 

e-9-14-f-ll-16-g 
These paths are unequal in length, as will be noticed from 
the drawing, when the brush which bears on the commu- 



Armature Winding 1181 

tator segments b, and c, has moved from this position. In 
order to make all the paths of equal length, the number of 
coils must be a multiple of the number of pairs of poles. 
For example, 16 conductors (8 coils) with a four-pole field 
(2 pairs of poles), would give uniform paths, each contain- 
ing an equal number of coils. The objection to this arrange- 
ment lies in the fact that four coils would be short-circuited 
at the same time. An examination of Fig. 524 where the 
number of coils is not a multiple of the number of pairs of 
poles, will show that four coils are not short-circuited at 
the same time. Where the number of coils is comparatively 
large the objection to the unequal length of the paths is not 
of so great importance. Where slotted armatures are used, 
the same conditions as just stated apply. It is quite evident 
that instead of having the conductors placed around the 
outside of the periphery of the armature, these conductors 
could be arranged in suitable slots. For instance, in Fig. 
528 each pair of conductors such as 1 and 2, 3 and 4, etc., 
could be placed in separate slots, in which case the same 
diagrams would apply, it being customary to consider the 
even numbered conductors as lying in the lower layer, and 
the odd numbered conductors as lying in the upper layer. 
As the number of conductors must be even, it is plain that 
there can be either an even or odd number of slots, but the 
number of conductors per slot must be such that the total 
number of slots, times the number of conductors per slot, 
must be an even number. 

In Fig. 529 is shown an arm'ature similar to the armature 
previously shown in Fig. 524. There are exactly the same 
I number of conductors and commutator segments. The con- 
ductors are placed on in the same positions, and the con- 
mections on the back of the armature are identical with 
I those of the previous figure. The distinguishing feature of 



1182 



Steam Engineering 



this armature lies in the method of connecting the various 
coils to each other^ and to the commutator segments at the 
front of the armature. Where^ in the previously described 
armature connection^ each coil after making a turn of the 
armature^ was carried back to a commutator segment ad- 




FiG. 529 

jacent to the one from which it started; in the present case 
the end of each armature coil is connected by means of a 
commutator segment^ to a coil some distance in advance 
of it. 

The developed winding clearly shows the manner in which 
this connection is made. It will be seen that the conductors 



Armature Winding 



1183 



are so connected that the current induced in each is in the 
same direction as that in the remaining conductors of the 
series. It will also be noticed that the developed winding of 
each element forms a sort' of wave and this winding is there- 
fore known as a ^Vave^^ winding. 

The scheme previously described may be employed to get 
a clearer understanding of this winding. This consists in 
drawing a circle^ and dividing it with as many intersections 
as there are conductors on the armature^ and then drawing 
a series of connecting lines through the various points^, as 



t 








Fig. 530 



shown by the winding table. The lines on the outside of 
the circle are to be considered as the rear connections of the 
armature^ and the lines inside the circle^ the front connec- 
tions^ or those connections running to the commutator seg- 
ments. Tracing out the winding (or its development, Fig. 
530), it will be seen that, starting from any one point and 
following out the winding circuit, every conductor is passed 
over once, and the winding finally returns on itself. 

The spacing or pitch for the rear is 5, being the same 
as that used for the lap winding, the conductor passing to 
the rear of the armature along 1, and returning along space 



1184 Steam Engineering 

6. The spacing at the front of the armature differs from 
that of the lap winding in that it is not carried back, but 
advances 5 spaces forward. The formula previously used 
for determining the number of conductors and the spacing 
may be applied in the present case. 



y= 



n^b +iy 



In Fig. 529. 

n, the number of poles=4; 

z^ the number of conductors=18; 

b, the number of conductors to a coil=:3. 



(¥..) 



jT— — I — I =4 or 5. 



For four-pole machines this formula simplified is z= 
4y + 2. In Fig. 529 z=4X5— 2=18. 

While the front and back spacings in the drawing shown 
are alike, i. e., 5 and 5, it is also possible to have these 
spacings differ. It is evident that the average spacing must 
be approximately equal to the total number of conductors 
divided by the number of poles, as the winding in passing 
around the armature from one commutator segment to the 
one next to it, comes under each pole piece. In the ex- 

z 
ample shown in Fig. 529 — is equal to 4^/2^ the average 

n 

spacing may, therefore be taken as 4, in which case the 
front spacing could be 5, and the rear spacing 3. 

The pitches at the front and rear of the armature must 
be odd, for, as has already- been explained, the even num- 
bered conductors are considered as returns for the odd num- 
bered conductors. 



Armature Winding 1185 

The winding table for this armature is 

a-l-6-f 

f-ll-16-b 

b-3-8-g 

g-13-18-0 

c-5-lO-h 

h-15-2-d 

d-7-12-i 

i-17-4-e 

e-9-14-a 
The two paths from the — to the + brush are : 
i-17-4-e-9-14-a-l-6-f-ll-16-b-3-8-g ) 

+ 

i.l2-7-d-2-15-h-10-5-c-18-13-g ) 

It will be seen that one path contains one more coil than 
the other and that, with narrow brushes, only one coil is 
short circuited at a time. 

We have thus far been studying armature winding from 
a theoretical standpoint. 

It is now in order to devote a space to the practical side. 
In the applicaton of the wire, the first thing in order is 
the proper insulation of the slots wherein the wire is to 
rest. The most suitable materials for this purpose are 

Shellaced paper, or cloth. 

Shellaced cardboard. 

Thin fibre, 

Mica. 

After the slot has been carefully insulated we may begin 
to apply the wire. Figure 531 illustrates two methods of 
doing this. In the first method shown at a the winding is 
begun in one corner of the slot, and continued in regular 
order, progressing first from left to right, until one layer is 
finished, and then from right to left until the second layer 



1186 



Steam Engineering 



is complete. By this method we can seC;, by referring to the 
figure^ that the last turn of the second layer comes in very 
close contact with the first turn of the first layer. The same 
condition will exist with every other layer in the same coil. 
The result of this is a great liability to abrasion in the first 
place^ further a great liability of the insulation being 
pierced^ should the coil be wound with a great number of. 
turns^ so that a great difference of potential would exist 
within it. We must bear in mind that the insulation of 




Fig. 531 



armature wires is very thin^ economy of space being a great 
consideration in all cases. 

By the above method of winding another great disadvan- 
tage is introduced. The lowest coil of wire being so tightly 
hemmed in^ and at the same time there being considerable 
necessity for handling the wire, the end of which is pro- 
jecting, there is much risk, of breaking it off short. If this 
occurs it becomes necessary to unwind the whole coil in i 
order to get at this wire for repairs. 



Armature Winding 1187 

In order to avoid these elements of trouble^ the method 
now to be described is extensively used. Take of the wire 
that is to be wound upon the armature^ sufficient to make 
one coil; the amount required can best be determined by 
winding one coil temporarily, and then unwinding it and 
using it to measure the other coils with. Take one of the 
wires so obtained and mark the center of it and place it 
exactly in the center of the slot as shown in Figure 531. 
Now begin winding from the center, to one side until that 
side is filled, next begin winding the other side in the same 
way and continue winding the second layer in the same way, 
half from each side, until the slot is filled. By this method 
if the number of layers is even, the two ends of the coil 
will finish side by side in the center ; if there is an uneven 
number of layers the two ends of the coil will be at opposite 
sides. It will make no particular difference which is the 
case. 

The full difference of potential of the coil will exist 
between the two wires of the last layer which lie side by side, 
and a difference of potential of a lesser degree between the 
two middle wires of each layer. It might, therefore, be 
advisable, where the coil consists of a number of turns, to 
provide an insulating layer between the two halves of the 
coil. 

When the last layer is placed on the armature great care 
should be exercised to see that it finishes off smooth. If 
possible avoid the condition of wires shown in Fig. 531. 
The wire at the right is likely to work down in time, and 
thus leave a loose wire above it that may work down and 
cause trouble. 

A wire in the position of the one shown in Fig. 531 
exeats a leverage on the other wires, and will gradually force 
its way down. 



1188 



Steam Ertgineering 



If the armature to be wound, has no slots, a few clamps 
(Fig. 532) will serve to hold the wire in place while a coil 
is being wound. 

Before starting the winding, tape should be laid on the 
armature, leaving it long enough so that it can be used to 
tie the coils together when tRe clamps are removed. Each 
wire should go to its proper place, and by no means cross 
any other wire below it so as to form a bulge. The strain on 




Fig. 532 



the wires of an armature, whether dynamo or motor, is at 
times very severe, and if there is any flaw it will surely 
show itself. 

In the case of fine windings, each layer as it is put in 
place should be thoroughly soaked with shellac. No cur- 
rent, except of a very low potential from a small battery, 
should be used either for testing or any other purpose until 
this shellac is dry. Shellac until dried is a conductor and 
may be pierced by the current and thus leave a gap, through 
which at a later time current may leak. An armature of 



Armature Winding 1189 

this kind is usually baked at a high temperature for 24 
hours. 

As an illustration of the great care that is advisable in 
the insulation of armature wires, we may state that some 
manufacturers place the magnet windings into tanks from 
which the air can be exhausted. After the air Is withdrawn 
from the coils, the insulating compound is allowed to flow 
into the tank until the coil is submerged. TJiis allows the 
insulating compound to enter into the most minute open- 
ings that may exist between the wires. Air pressure is 
afterward applied to make certain that the interior of the 
coil is reached by the fluid. 

As each coil is finished it may be tested for correctness 
of winding by a battery of two or three cells, and a small 
galvanometer. The battery if always applied in the same 
way must always produce the same deflection on the gal- 
vanometer (see Fig. 546) ; if it does not do this the coil 
in question has been wound wrong. It is not always neces- 
sary to unwind the coil to correct this ; frequently all that 
will be necessary is to connect the terminals of the coil in 
the opposite way from the rest. As this, however, often 
necessitates a crossing of the wires it is sometimes objec- 
tionable. 

When all of the coils have been wound upon the armature 
the end of each coil is to be fastened to the beginning of 
the next. Both are then fastened to their respective commu- 
tator bars. It is well to tape the two wires together : this 
leaves them stronger to resist mechanical interference, and 
also occupies less space. This latter is an important con- 
sideration where there are many coils. 

The commutator sections are sometimes provided with 
screws to hold the wire, but oftener the wires are soldered 
directly to the commutator segments. This latter is the 



1190 



Steam Engineering 



safest method but may cause some trouble should it be 
desired to remove the commutator for repairs. 

The next step is the placing of the binding wires. These 
are to hold the wires of the armature in place and must 
always be used^ unless the slots on the armature are of the 




j^ 






Fig. 533 



nearly enclosed type. The binding wires are wound upon 
the finished armature as shown in Figure 533. After plac- 
ing a band of insulating material^ such as mica^ where the 
wires are to go^ begin by taking one or two turns of wire 
around the armature with the spool ; draw these as tight as- 
possible and solder as indicated by arrow in the drawing. 



Armature Winding 1191 

Now proceed, and put the balance of the necessary turns in 
place by revolving the armature and holding the spool with 
the wire stationary. In this way the winding can be placed 
very accurately and close together. After a sufficient num- 
ber of turns have been placed they are all soldered together 
over the whole circumference to avoid possibility of any of 
the wires breaking loose and causing damage. 

Where the winding begins and ends a thin piece of brass 
should be laid under the wire before it is wound on. After 
the winding is finished this is bent over and soldered. Iron 
and steel should not be used for binding wires; although 
the section may not be large, they would always increase the 
magnetic leakage that would to some extent lessen the 
E. M. F. of the machine. The size of the binding wires 
used ranges from number 20 to number 10. The latter is 
used for the larger machines and the first for the smaller. 
Usually about one-third of the armature is covered by stich 
wires. 

The student of drum armature winding will save him- 
self considerable worry, and mental tribulation if he will, 
at the beginning, construct for himself out of a large spool 
or some similar circular object a little imitation armature, 
upon which he can wind with strings such coils as are 
herein described as being in use on armatures. These little 
experiments will be more realistic if, for this purpose the ar- 
mature of some old fan motor can be procured. Such an 
; armature should preferably be of the slotted kind; if the 
wooden spool above referred to is used its periphery should 
!be divided off into the proper number of spaces by insert- 
ing suitable nails thereon. Much can be learned in this 
way regarding armature winding that can never be fully 
grasped in any other way. 



1192 Steam Engineering 

QUESTIONS AND ANSWERS. 

818. Can the properties of a dynamo be accurately cal- 
culated from any of the formulas given for that purpose? 

Ans. No. The accurate design of a new type of dynamo, 
and an armature as well, is as much a matter of experiment 
as it is of calculation. 

819. AVhyisthis? 

Ans, There are so many factors involved in the calcu- 
lation that cannot be accurately determined until a ma- 
chine of the exact dimensions of the one under considera- 
tion has been built. 

820. What are the principal factors that are so trouble- 
some to determine? 

Ans, The permeability of the iron, the resistance of 
the magnetic circuit, the tendency to leakage of the lines 
of force, the exact proportion of the dead wire, the reaction 
of the armature, the losses due to Foucault currents. 

821. Are not the causes of all these losses well under- 
stood ? 

Ans. They are, and it is easy enough to tell what must 
be done to lessen any or all of them. It is merely their 
exact value which is indeterminate until the machine in 
question is in operation. 

822. What is the chief precaution which must be taken 
» this account. 

Ans, It is necessary to leave some part of the controlling 
ti^fluences so that they can be readily varied and thus adjust 
the machine so that it will be exactly right when it is finally 
finished. 

823. How can this best be. done? ^ 

Ans, Since it is manif es^ljf VGiy; t^liblesome to rewind 
an armature, if perchance too great or too small a number 



Questions and Answers 1193 

of wires have been placed upon it, the proper factors to be 
arranged to be variable are : the speed, and the strength of 
the field. In some cases the speed, even, is not changeable, 
and the whole duty of compensating for misjudgment in 
the calculations falls upon variations of the field strength. 

824. Can the whole regulation be accomplished in this 
way? 

Ans. It can, and in most cases this is the method relied 
upon. It is very easily accomplished by this method if we 
arrange to have the fields magnetized to only a low degree 
of saturation. By doing this, however, we are led to provide 
field magnets whose capacity is far in excess of what we 
believe to be necessary and, therefore, more expensive. So 
that again in the last consideration it behooves us to experi- 
ment before we definitely determine the exact proportion 
of our dynamo or motor. 

825. Are there any formulae that can be used in deter- 
mining the exact proportions? 

Ans. There are, and they are given below. These will 
materially assist the student in forming an idea how the 
different parts can be adjusted to bring about the desired 
final result. For the following formulae we shall adopt the 
attached set of symbols : 

' Let P=the total number of lines of force, or fiux, 
V=the number of volts to be generated, 
S=:the number of slots in the armature, 
E.P.S.=the number of revolutions per second, 
W:=the number of wires per slot. 
Then, to find the number of wires necessary per slot where 
the speed and fiux are fixed: 

io«xv 



W.=:- 



FXSXR.P.S. 



119':1: Steam Engineering 

To find the necessary speed where the number of wires, and 

the flux^ are fixed : 

lO'XV 
E. P. S.= 

FXSXW 

To find the necessary strength of fields where the wires 
and speed are fixed : 

lO^XV 

SXR. p. S.XW 
To find the volts generated : 

_PXSXWXE. P. S. 



10« 

826. Are these formnlse used in actual practice to deter- 
mine the size of wire^ speedy etc. ? 

Ans. These formulae are of value principally in check- 
ing up the actual calculations made. 

827. How is an armature actually designed? 

Ans, In actual practice whenever a, new dynamo or 
motor is to be constructed it is^, so to speak^ built up around 
the armature. That is to say^ the armature must first be 
designed^ and the other parts made to fit around it. 

828. What is the principal consideration to be taken 
into account? 

Ans. In order to deliver a certain current, the number 
of poles, etc., being fixed, which is with rare exceptions the 
case, we must use a certain size wire. 

829. Is there no choice whatever in the size of wire 
for a given current? 

Ans. There is some choice. In most cases the heating 
of the wire on the armature determines the size of wire to 
be used; in other cases it is the drop in potential at the 
terminals of the armature that governs. 



Questions and Ansiuers 1195 

830. How does the size of wire affect the heatings and 
the loss of potential? 

Ans. Both of these losses^ and the troubles occurring 
from them^ are lessened by selecting wires of greater 
diameter. 

831. How do yon proceed to calculate the necessary size 
of wire ? 

Ans. The number of wires^ and the dimensions of the 
armature for any given purpose can be found by trial cal- 
culations only. By this we mean that^, unless we are very 
lucky, we shall have to make a number of calculations^ 
using, perhaps, different dimensions and wires before we 
get the result that suits us best. 

832. Give an example. 

Ans. As an example let us take an armature 8 inches 
in diameter and 8 inches in length and see what it will 
do for us. Such an armature has a cross-section of 64 sq. 
inches and, assuming a flux of 30,000 lines of force per 
square inch, we have a total flux of 1,920,000 lines through 
the armature. We first find how often one wire must cut 
this number of lines of force to generate, say, 110 volts. 
To do this we first divide 110X100,000,000 (which is the 
total number of lines to be cut per second) by the total 
flux, 1,920,000, and obtain as the result 5728. Next, to 
get the necessary number of wires to be placed upon the 
armature, we must divide this quotient (5728) by the 
number of revolutions the armature makes per second. If 
our armature revolves at the rate of twenty revolutions per 
second (1,200 per minute) we shall need one-twentieth 
of 5,728 wires placed upon it. This amounts to 286. As 
our armature, 8 inches in diameter, has a circumference of 
25.12 inches, this gives us a wire running about 11 per 
inch. If there is to be but one layer, this gives a number 



1196 Steam Engineering 

12 wire. As the two sides of the armature are in parallel 
we have a capacity of 2 times 14.31 amperes according to 
Table 50. If we decide to use two layers^ we can take a 
No. 6 wirC;, 5.5 per inch, and obtain a capacity of 56.55 
amperes. It may be stated in explanation of the calcula- 
tions here made that each wire in the course of one revolu- 
tion of the armature cuts the total flux two times; but as 
the two halves of the armature are in parallel, each side 
must produce the full voltage by itself. 

833. How much radiating surface is usually allowed per 
watt of energy used up ? 

Ans. That depends very much on the work for which 
the armature is intended. If it is for a railway motor, 
which is entirely enclosed, and almost constantly in use, it 
is much more than, for instance, an elevator in a private 
residence where there is but very little use, and only at long 
intervals, so that the armature has time to cool off between 
one riin and another. Table 50 is based upon the require- 
ment that there shall be three square inches of radiating 
surface for each watt of energy expended in the coils. 

834. What radiating surface is allowed for each watt 
expended in the case of an armature ? 

Ans, This amount varies in different machines, being 
as low as 1 square inch per watt, and as high as three square 
Anches per watt. About 1.75 square inches per watt ex- 
pended can be considered as a fair average for armatures 
\nd about 3 inches per watt expended for field coils. 

835. How is the table referred to (Table 50) made up? 
Ans, This table is figured from the formula, 

ES 
3XE 



J 



Questions and Answers 1197 

E S being the radiating surface^ and E the resistance of a 
unit of length of the wire under consideration. This form- 
ula gives the current allowed where the wire is wound in 
one layer. As we add more layers we must;, with each suc- 
cessive layer^ reduce the current^ so that the square of the 
current multiplied by the resistance (which equals the 
watts) shall remain always the same, because increasing 
the depth of the winding does not affect the radiating sur- 
face of the coil. 

836. The table gives the carrying capacity only to a 
depth of six layers ; how is the carryng capacity of a greater 
number of layers to be found? 

Ans. To do this we refer to Table 50 and select from the 
column headed I^ the number pertaining to the wire in 
question. This number represents the square of the cur- 
rent permissible with one layer of wire. Divide this num- 
ber by the number of layers it is intended to use, and extract 
the square root of the number so found. The result will be 
the carrying capacity of the wire in question, wound to a 
depth of that number of layers. As a general guide we may 
bear in mind that, as we multiply the number of layers by 
4, 16, 64, 256, we, each time, decrease by one-half the 
carrying capacity of the wire. From this we can see that 
the capacity of the wires after a certain number of layers 
have been considered, decreases very slowly, though very 
fast with the first few layers. 

837. Is there need of very great accuracy in these 
calculations ? 

Ans. Great accuracy is not necessary in these calcula- 
tions. We can always lengthen our armature a little by 
adding a few punchings, should the potential be insufficient, 
and we can always vary the speed and strength of field con- 



1198 



Steam Engineering 



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Questions and Answers 



1199 



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1200 Steam Engineering 

siderably. Adding to any of these would tend to increase 
the E. M. F. of the armature, but not its capacity in 
amperes. 

838. If the capacity of the armature is not sufficient, 
how do we proceed ? 

Ans. Take the next larger wire, or such a wire as will 
give the desired capacity, and from the diameter of this 
wire figure out a new armature. By using the same num- 
ber of wires of a larger diameter, a greater cross-section of 
armature is obtained. 

839. Do these considerations apply equally well, 
whether an armature is slotted, or not? 

Ans, The only difference is that with a slotted arma- 
ture it is necessary to take into consideration the length of 
the winding space in the slots only, not the total circum- 
ference of the armature. There is also considerable loss of 
flux through the teeth of the armature so that the flux must 
be assumed less. A great flux is obtainable, however, with j 
the same field winding, as the magnetic circuit -of a dynamo 
with a slotted armature has less resistance. 

840. How do you proceed in the case of a slotted arma- 
ture? 

Ans, If we have an armature provided with slots of a 
fixed size we can but arrange to accommodate ourselves to 
it as best we may. It may be that the slots are of such size 
that the wire we have selected through our calculation will 
not flU out the slot well, and we must, therefore, try some 
other size wire. In this case it will be preferable to select 
a larger size wire if practicable. This had best be tried by 
actual experiment. As the wire often will not fill out the 
slot quite fully, calculations are not exactly reliable. Any 
deficiency can, of course, be made up by filling in with insu- 



Questions and Answers 1201 

lation. The number of wires per slot is found by dividing 
the total number of wires by the number of slots. 

841. How can the size of a slot capable of holding a 
certain number of wires be determined? 

Ans. The approximate depth of the slot can be obtained 
by multiplying the diameter of the wire to be used by .86 
and this by the number of layers placed over each other. 
The result will be exact if the wires lie as shown in Figure 
512. The width of the slot can be found by multiplying the 
diameter of the wire by the number of turns per layer. It 
will be seen from the figure that each alternate layer will 
contain one turn less than the first. 

842. Can slots be proportioned so that they will accom- 
modate any number of wires ? 

Ans. The slots must be proportioned to the number 
of wires to be used, and the number of wires per slot must 
be carefully considered. If the number of turns per slot 
are few, the wires should be placed as shown in Figure 513. 
If there are many, according to Figure 512. Which of these 
two methods is to be used will have a bearing on the num- 
ber of wires per slot. The total number must be a multiple 
of the number of layers. 

843. After we have selected our wire, and determined 
the number of wires to be used, can we form some idea of 
what the losses in the armature will be? 

Ans, We can easily figure the approximate loss of volt- 
age in the armature from the size of wire to be used. To 
do this we first find from Table 50 the resistance per foot of 
the wire in question, and then measure the length of wire 
in one coil and multiply the resistance by the number of 
feet. If we have a bi-polar armature we again multiply 
this by half the number of coils (the two sides being in 
parallel). Since the loss in voltage is equal to the ampere?? 



1202 Steam Engineering 

multiplied by the resistance, we need but to multiply the 
resistance so found by half the total current to find the 
loss in voltage that will occur. This loss is, of course, in 
direct proportion to the current. This loss is not of much 
importance in ring armatures, or in drum armatures either, 
when they are working with small currents, or on constant 
current work such as arc lighting; but with heavy, and 
variable currents it is a very important matter, and the 
lower the losses can be kept, the better. 

844. Are there any special considerations to be borne 
in mind while winding the different coils ? 

Ans. It is quite important to see that each coil contains 
the same number of turns, and that these fill out the same 
relative space. 

845. Why is this so important? 

Ans, We have already seen that the two halves of the 
armature are ,generating in parallel, that is, the currents 
from the two sides meet at the positive brush and flow out 
to the line, and return by the negative side to the armature. 
If now there are fewer turns of wire on one side than on 
the other, or if there is one weak coil in the armature, one 
side or the other will always be generating a greater E. M. F. 
than the other and consequently current from the high pres- 
sure side will flow through the winding of the low side. 
To see this more clearly refer to Figure 514. On the arma- 
ture there shown, there are 16 coils. If this armature is to 
generate 40 volts, each coil will be called upon to produce 5 
volts. Now suppose one of the coils to be cut out of the 
circuit entirely. It is clear that at all times except when 
the dead coil is at the neutral points, there are 8 coils gen- 
eraing on one side against 7 on the other; i. e., 40 volts 
against 35. In order to find the current that would flow in 
such an armature while on open circuit, subtract the low 



Questions and Answers 1203 

voltage from the high, which leaves an active voltage of 5. 
If the resistance of the armature were .1 ohm a current of 
50 amperes will be circulating a great part of the tii^.e. 

846. Wliy would this not be a eonstant current? 

Ans. For the reason that this current would be con- 
stantly changing in direction, because the strong side of the 
armature would be first on one side, and then on the other, 
of the fields. On open circuit a perfect armature would 
generate no current whatever; with an armature as de- 
scribed the current mentioned would always be flowing 
toward the coil which is cut dead. 

The current would be changing in strength, because dur- 
ing the time the dead coil is short circuited by a brush it 
would be balanced by another coil under the opposite brush 
which for the moment is also dead. Consequently during 
that time the armature would not be generating at all. 

847. How would this inequality of generation manifest 
itself if the dynamo were generating current ? 

Ans, If the dynamo were generating current this con- 
dition would greatly reduce its capacity. The current flows 
only in obedience to the pressure, and as this would be 
variable the current would of course also be variable. 

848. Are differences in potential between different part^ 
of an armature caused by any other conditions in the ar- 
mature? 

Ans. Such differences are sometimes caused by the loca- 
tion of the wires of different coils. Other things being equal 
the E. M. P. generated by any coil varies with its distance 
from the center of the armature. It can readily be seen 
that the farther a wire is from the center, the greater will 
be the area enclosed and therefore the greater the number 
of lines of force cut by it. 



1204 Steam Engineering 

849. What other cause is there for inequality of genera- 
tion? 

Ans. Another cause for inequality of generation be- 
tween different coils lies in a difference of resistance. 

850. Does this affect the generation on open circuit? 
Ans, It does not. We have already seen that the loss 

in potential in any circuit is proportional to the current 
flowing, multiplied by resistance of the circuit in which it 
flows. Therefore the drop in potential in any coil is in 
proportion to the current being taken from it. If one coil 
therefore has a much higher resistance than the others its 
potential will fall much more, and the side of the armature 
on which it happens to be will be of lower E. M. F. than 
ihe other, and there will be the same tendency to a vacillat- 
ing current as in the case of coils of uneven number of 
turns. The variations will, however, not be near so great, 
for an excessive current flow from the strong side will re- 
duce the pressure on that side, and the checking of the cur- 
rent on the low side will raise the pressure there, so that a 
l)alance will be obtained without any great current flow. 
The main danger of introducing inequality in the resistance 
•of the winding lies in the winding of the inside of the coil 
with Gramme ring armatures. The space for the winding 
at this point is necessarily of a different shape than that 
on the outside, and there are also the spokes of the arma- 
ture to contend with. 

851. How many methods of armature winding are in 
.general use ? 

Ans. The methods of armature winding are very numer- 
ous. For the present we shall confine ourselves to the 
jnethods used with hand winding on cylinder armatures. 

852. Which is the most simple of these windings? 



Questions and Answers 



1205 



Ans, The simplest one of these windings is that shov;n 
in Figure 534, and we shall take this one for the purpose 
of demonstration. It will be noticed that in this figure there 
are 12 slots in the armature and 6 commutator sections, 
indicated by the wires twisted together. • 

853. Is it necessary that this proportion of slots and 
armature coils exist? 




Fig. 534 

Ans. It is not; in fact it is not at all desirable that this 
proportion should exist, but this proportion is very con- 
venient for winding, as we shall see. 

Begin winding by selecting two of the slots located 
opposite each other, as shown in the figure, and starting 
at 1 wind into those slots as many turns of wire as has been 
determined there should be and bring the last end of the 



1206 Steam Engineering 

coil to the commutator section next the one from which we 
started. 

854. Should this be to the one in front of^ or behind 
the section from which the winding started ? 

• Ans. This is immaterial. In actual practice there 
should not be any commutator sections in place while, wind- 
ing. They would be very much in the way. Instead^ tie the 
two ends of the coil together and properly mark the be- 
ginning and end. 

855. Are all coils wound in the same way? , 

Ans. They are; but in this case we must skip one slot 
at each subsequent coil^ in order to make them come out 
right in the end. That is to say^ if the first coil is wound 
into 1^ 1^ the second must be wound into 2^ 2, the third 
into 3^ 3^ etc. 

856. Why is this? 

Ans. As each coil fills out two slots, we have with the 
third coil finished half of the armature. If we were to wind 
the slots in consecutive order, the connections for the com- 
mutator would all come on one side, and we could do noth- 
ing with the armature. As we now continue in the order 
we have started we finally complete the entire winding and 
have the beginning and end of one coil opposite each com- 
mutator section. We can now fasten the beginning of the 
first coil to its proper commutator section, and the end of 
it to the next one. It will be immaterial whether this be to 
the section ahead, or behind the starting section, but, which- 
ever way we start, we must be sure to continue in the 
same way. 

857. This being the most simple method of armature 
winding, why are not all armatures wound in this way? 

Ans. The great objection to an armature wound in tills 
way is that the coils become too large. 



Questions and Answers 1207 

858. Why are large coils objectionable? 

Ans, In order to understand why large coils are objec- 
tionable we refer to the commutator shown at the right of 
Figure 534. Here a brush is shown bridging two commu- 
tator sections and short circuiting the coil connected to 
them. The coil indicated by the black line is the same one 
shown in the slots 1^ 1^ and the connections are identical. 
It can readily be seen that all of the coils will in turn 
become short circuited in the same way in the course of 
every revolution of the armature. 

■ Kow in the first place assume that the coil when thus 
short circuited is in an entirely dead part of the field. 
When a brush short circuits such a coil it takes all the 
current away from it. When the brush leaves the forward 
section of the commutator this short circuit must be broken, 
and current must be again established through the coil. 
As every coil possesses some inductance -(which acts for an 
instant like a very high resistance), there is a tendency for 
the current in that half of the armature to jump across the 
insulation between the commutator sections, rather than 
pass through the coil. If this occurs there is destructive 
sparking. The greater the number of turns of wire in any 
coil, the greater will be the likelihood of this taking place. 

859. Is this the main reason why the coils on an arma- 
ture should be made up of few turns of wire ? 

Ans. It is not. The most important reason for this is 
the following : If the coil is not in an entirely "dead^^ part 
of the field there is always some current generated in it 
during the time the brush is in the position discussed above. 
This current circulates in the coil during the time the 
, brush holds it on short circuit, without appearing in the 
' outer circuit, and is therefore a dead loss. It furthermore 



1208 



Steam Engineering 



tends to heat the coils. Because two of the coils are nearly 
always on short circuit in this way^ the loss and the heating 
are considerable when the coils are large. When these cur- 
rents are broken by the commutator section sliding from 
under the brush, they also make themselves evident by 
severe sparking, if the coils are large. 




Fig. 535 

860. Are there any more reasons why large coils are 
objectionable? 

Ans. Another reason why large coils in an armature 
are objectionable can best be understood by reference to 
Fig. 535. A simple dynamo such as is depicted in this 
figure delivers a current graphically illustrated by Fig. 536. 
It will be seen that this is really an intermittent current. 
This is because the dynamo has but one coil, and while 



Questions and Answers 1209 

this is at the neutral points^ nothing is being generated. 
The current therefore fluctuates from to its maximum. 
If we add one more coil the current line becomes as shown 
in Fig. 537^ and the greater the number of coils the smaller 
becomes the percentage of non-generating coils, and the 
nearer does the current line approach a straight line show- 
ing a steady value. 

861. Why cannot small coils be wound in the manner 
shown in Fig. 534. 

Ans, It is desirable to make the coils as small as pos- 
sible. The ideal coil would consist of only one turn. Now 

r\r\r\r\r\r\r\r\ 

Fig. 536 




Fig. 537 

as long as we wind only one coil into one slot we shall 
have the coils needlessly large. The number of coils is 
limited by the number of commutator sections, and unless 
we wind two coils into each slot (as we can see from Fig. 
534) we can have but half as many commutator sections 
as there are slots. In order to get a small coil it is there- 
fore necessary to get two coils into each slot. 

862. Can this be done in more than one way? 
. Ans, This can be done according to any of the plans 
i shown in Fig. 538. In this figure the black and white 
1 circles respectively represent the wires of the two different 
coils wound into the same slot. 



1210 



Steam Engineering 



We have already seen under ring armatures^ that wires 
of different coils should all be of the same distance from 
the center of the armature^ so as to cut the same number 
of lines; it follows^ therefore^ that the plan showing one 
coil wound over the other should not be used where it can 
be avoided. 

863. How do you manage to place two coils in one slot? 

Ans. In order to understand exactly how this is done 
let us consult Fig. 539. This figure is a duplicate of Fig. 
534 with the exception that now we have as many com- 
mutator sections as there are slots in the armature; The 



Y//^y\ 






'//. 






//> 



y/. 



^/^. 



'/j 



» /<- 



^^ 



V//0 



>^v 



^'. 



>''^. 



V 



'/'/ A '/'- ^// ^^/ / :C t ''c^W//^^ '-> :^//>^''' 

Fig. 538 

black circles represent the wires of one set of coils^ and the 
light those of the other. 

The simplest method of winding two coils into one slot 
is^ first to wind one coil complete^ filling half the slot^ then 
turn the armature half way round and wind the second 
coil over the first. As this^ however^, gives two coils of dif- 
ferent lengths and resistance, and also cutting a different 
number of lines of force, such a winding is seldom used. 
A better way is the following: Cut two wires of sufficient 
length so that each will make one coil, place the armature 
upon two crossbars of convenient height so that it can be 



I' 



i 



Questions and Answers 



1211 



easity turned over when required. Mark all of the slots 
with appropriate numbers according to the plan of wiring 
selected^ so there may be no confusion when the work is 
started. A very good plan is shown in Fig. 534. This 
plan gives the smallest head of any because there are al- 
ways two coils running parallel to each other across the 
ends of the armature. Thus we have three lavers of coils 




Fig. 539 



4 crossing over each other^ while with any of the others 
we should have six. But in order to get the advantage of 
I this smaller head^ we cannot wind the coils in the order 
'given in the explanation of this winding. It becomes neces- 
sary to wind completely, at the same time, the two coils 
that are running parallel with each other across the ends. 
To do this requires more e;xperience and forethought, than 
iJ the way previously described. 



1212 Steam Engineering 

Begin the winding with the coil marked 1^ and make 
one complete turn and fasten the two ends of the wire to- 
gether temporarily if more turns are to follow, or fas- 
ten each to its proper place on the commutator, if there 
is to be but one turn. Now turn the armature half way- 
round and wind the other wire in the same way. If there 
are to be more turns, continue to wind the second turn. 
After this is finished turn the armature back to its original 
position and wind the first wire again. Eepeat in this 
manner until the desired number of turns in both coils have 
been obtained. By reference to Fig. 539 we note that the 
windings do not skip slots as in Fig. 534. This is easily 
explained when it is noticed tiiat each slot contains two 
conductors and that at each step we skip one conductor as 
before. 

It is not necessary in actual practice to turn the arma- 
ture around as above suggested. This was suggested merely 
as a beginning to make the principle more plain. The 
same result can readily be obtained if the armature is left - 
stationary. The windings need merely to be so arranged 
that they will come right for connection to the commutator 
as shown in the cut. 

It is well enough to use care that all of the coils are wound 
in the same direction, but it will not materially affect the 
operation, if one part of the coils are wound left hand, and 
the others right hand. The essential point is to see that 
they are so connected that the magnetism resulting from a 
current flow through the coil will be the same in all. II 
it is different in one coil from the others it can easily be 
rectified by simply changing the end connections of the 
coil in question. 

864. Are all armatures hand wound ? 



Questions and Answers 



1213 



Ans. Hand winding is customary with the smaller 
drum^ and ring armatures only. It is the only method 
that can be used with ring armatures^ and also with drum 
armatures where the wire is to encircle the whole armature. 
The larger dynamos are now made mostly multipolar, and 
in these the coils do not return at nearly, or wholly, diam- 
etrically opposite points as they do in those machines we 
have so far had under consideration. With multipolar ma- 
chines the armature is divided into as many sections as 
there are poles. While it is possible to work any regularly 







Fig. 540 



wound drum, or ring armature in connection with many 
poles, it is not customary to do feo. In general the coil 
wound on a multipolar armature has its return winding 
spaced about as far from the first turn, as it is from the 
center of one pole piece to the center of the next one. 

865. How does this affect the winding? 

Ans, This gives us a winding of much lower resistance 
'than could otherwise be obtained, and the magnetic circuit 
is also much better. Furthermore, it makes possible the 
(use of so-called ^^former coils.^^ 



1214 



Steam Engineering 



866. What is a former coil? 

Ans. A former coil is one that is wound upon a former, 
i. e., one that is wound complete before it is placed upon the 
armature. 

867. How are such coils made up ? 

Ans. Figs. 540 and 541 show two styles of former coils, 
and the manner in which they are wound. In Fig. 540 the 
black circles represent strong pins fastened into a piece of 




•Fig. 541 

plank, or other suitable material. The wire is wound 
around these pins as indicated in the figure, as many turns 
being taken as it has been decided to allow for each coil. 
When the coil is thus completely wound it is taken from 
the pins, and the lower ends placed in a suitable clamp, as 
indicated by the broken line in the lower center of the 
figure. After this clamp is fastened onto the coil the tw6 
halves of the coil are spread apart, one being pulled to- 
ward the operator and the other pushed away from him at 



Questions and Answers 1215 

right angles to the clamp. In this way the coil is made to 
assume the shape illustrated in Fig. 542. Before winding 
a coil in this manner it is of course necessary to know ex- 
actly what length it must be^ and a pattern coil must there- 
fore first of all be prepared^ from which the spacing of the 
pins can be taken^ so that the completed coil will fit into 
the slots for which it is intended. 

868. How are such coils placed upon the armature? 

Ans. Begin placing the coils at any convenient slot, and 
lay them in, as indicated in Fig. 542. It is necessary to 
mark the beginning, and end of each coil, so that there 




Fig. 542 



may be no wrong connection when the wires are finally 
connected to the commutator. 

Before placing the coils the slots must of course be in- 
sulated as explained previously. We now continue to lay 
in coils until the whole armature is full, but when nearly 
full, the forward ends of the coils we are placing require 
to be brought under the first coils put in place. To do 
this it is merely necessary to raise up the first six coils, 
(in this case) and place the forward ends of the last six 
under them in the regular order. , . 

869. By what name is this winding known? 

Ans. This is known as the ^^evolute^^ winding. It will 
ibe noticed that when this winding is completed, the wires 
of the outer portion entirely conceal those of the inner, and 



1216 Steam Engineering 

thus give this style of winding its characteristic appearance. 

870. What other manner of winding multipolar arma- 
tures is there? 

Ans. Another method of forming coils is illustrated in 
Fig. 541. In this case the coil is first wound around two 
pins^ as shown at the top of the figure. The ends are then 
placed in clamps^ as indicated by the dotted lines at the 
top and shaded lines in the center of the figure. After 
these clamps are fastened^ the coil is turned one-fourth 
around, and the wires spread over the four pins, as indi- 
cated in the figure. 

871. How is this coil placed upon the armature? 




Fig. 543 



Ans. The coil formed in the manner above assumes the 
shape shown in side view in Pig. 543 and is placed upon 
the armature as there indicated, the manner of placing 
being the same as that of the previous coil. 

872. "What name is given to this style of winding? 

Ans. This is termed a *^^barreP^ winding and its charac- 
teristic appearance can be seen from the figure. 

873.^ Is it necessary to carry out the same kind of wind- 
ing on both sides of an armature? 

Ans. There is nothing- to prevent one from using one 
of these windings on one side of the armature, and the 
other on the opposite side. They cannot^ however, be com- 



Questions and Answers 



1217 



bined on the same side. The windings of large machines 
very often are made np of bars of copper made of special 
sizes to snit. These are often arranged as shown in Figs. 
544 and 545. Sometimes such bars are bare and laid into 
the slots with insulation loose on the sides and bottom and 
between the different bars of a slot. Such winding is often 
held in place by pieces of wood inserted into the slots as 
indicated in Fig. 543, the slots being specially prepared to 
admit of this. Where no such provision has been made the 
wires are held in place by the usual binding wires. 



"^x^ 



Fig. 544 



MOTOR ARMATURES. 

874. Is there any difference between the armature of 
motors and dynamos? 

Ans. Theoretically there is no difference between the 
armature of a dynamo and motor. In fact, many machines 
are placed in conditions in which their functions change, 
perhaps a hundred times per day, from that of generator 
to that of motor. 

875. Are there any special provisions necessary to make 
them operate thus ? 

Ans. No. This change takes place automatically, and 
the operation is so smooth that the observer will have no 
idea in which capacity the machine may be operating from 



1218 



Steam Engineering 



moment to moment. It is also no unusual thing for a 
dynamo working in parallel with other generators to be- 
come reversed, and instead of delivering current to the 
line, it will be drawing from it and running as a motor. 

876. What should one principally have in view in the 
design of a motor armature ? 

Ans. Motor armatures must be designed to produce a 
certain counter E. M. F. just as dynamo armatures are 
designed to produce E. M. F. In the case of a dynamo the 




Fig. 545 

power is measured by the product of the E. M. F. and the 
current, so in the motor the power is proportional to the 
product of the counter E. M. F. and the current. 

877. How do you proceed to calculate the winding for 
a motor armature? , 

Ans. In the same way as with a dynamo except that 

the E. M. F. should not be figured as high. The current 

V-v 
passing through a D. C. motor equals , where V is the 

volume of the line that supplies it; v the counter E. M. F. 
of the armature, and E its resistance. It is apparent that 
in order to get more power out of a given motor, its coun- 



Questions and Answers 1219 

ter E. M. F. must be reduced in order that a greater cur- 
rent can flow. 

878. How is this brought about? 

Ans. With a motor in operation this counter E. M. P. 
is reduced when the speed reduces^ on account of a heavier 
load. More current is thus allowed to flow until the power 
of the motor becomes equal to the work required of it^ but 
if the load exceeds the capacity of the motor it will take 
too much current^ and burn out the armature. If a motor 
is to be designed to operate at a certain speedy all of these 
facts must be taken into consideration^ and the wires so 
selected that when running at the required speedy the neces- 
sary counter E. M. F. will be generated. 

For illustration, take the same armature that was con- 
sidered in the previous section. In this case a No. 12 wire 
was required. This gave 11 turns per inch, and its car- 
rying capacity was 14.3 amperes. The dimensions of the 
armature were 8''x8'', requiring about 770 feet of wire. 
With this quantity of No. 12 the resistance is 1.39 ohms. 

Only one-half of this, however, is on one side, and only 
14.3 amperes pass on one side, so that the total E. M. F. 
to drive this current through the armature is 14.3X.697, 
which is 9.96. In order that this motor may allow the 14.3 
amperes to pass, its counter E. M. F. must fall to 9.96 
volts less than the E. M. F. of the line. If this is 110, the 
speed must slack off about 9 per cent in order that the 
motor may develop its full power. 

It is easily seen from this that, in order that the motor 
may operate at a fairly constant speed, the resistance of the 
armature should be made as low as possible. In practice it 
is generally made so low that a reduction of 1 per cent in 
speed wll bring about the required lowering of counter 
E. M. F. to cause the proper current to flow. 



1220 



Steam Engineering 



ARMATURE TROUBLES. 

879. How do armature troubles manifest themselves? 
Ans. Either by excessive sparking at the commutator, 

or by abnormal heating of the armature. 

880. What are the causes of such troubles? 

Ans. They may result from any one of the following 
causes: There may be a wrong connection of one, or more 
of the coils. Some of the coils may be grounded. There 
may be an open circuit. There may be a short circuit. 








-^ 



R 



GOO 



rh= 




Fig. 546 



The brushes may be improperly set. The brushes may not 
make sufficient contact with the commutator. The com- 
mutator may be rough or worn. The fields may be of 
uneven strength. 

881. How can a wrong connection of the coils be tested 
for? 

Ans, In order to see how this test can be made let us 
consider Pig. 546 for a moment. This figure shows the 
wiring of an armature connected to the commutator seg- 
ments exactly as it would be if it were taken off, and the 



Questions and Answers 1221 

coils separated without detaching from the commutator^ in- 
stead of being placed in an orderly manner upon the core 
of the armature. In other words^ the connections are ex- 
actly as in an armature. If we should now take the two 
wires of some supply of current capable of delivering a 
few amperes^ and connect these two wires to two adjacent 
commutator segments^ as shown at a, and i, it is clear that 
current would flow through the coil connected between 
these two sections^ and also through the other coils. The 
current has two paths: one through the single coil^ the 
other through the remaining seven coils in series. 

The current in the two coils flows in opposite directions^ 
with the result that a field of force is set up in the vicinity 
of the single coil. A suitable galvanometer placed at this 
point will be deflected in a certain direction. By revolving 
the armature and applying the test to each succeeding pair 
of commutator sections^ a number of deflections of the 
needle will be obtained. 

If all the coils are correctly connected these deflections 
will all be in the same direction. If one of the coils is con- 
nected wrong, a different deflection will be obtained. If 
one of the coils has been wound on in the wrong direction, 
it is not necessary to rewind it ; the connections can simply 
be reversed. 

882. What is meant by a ''ground'' ? 

Ans. An electrical connection between some current 
carrying part of the armature, and the metal armature 
frame. A ''ground'' is often caused by the insulating cov- 
ering of the wire breaking down, thus allowing the wire to 
come in contact with the iron core. 

883. How do you test for this condition? 

Ans. The simplest method of testing for a ground con- 
sists in taking a lamp or voltmeter and connecting it as 



1222 Steam Engineering 

shown in Fig. 546. Place one of the wires in contact with 
the iron core^ and the other in contact with the wire on 
the armature. If the lamp lights^, there is a connection be- 
tween the wire and the core^ and this should be removed. 

884. How is an open circuit located? 

Ans. Eeferring to Pig. 546^ connect the commutator 
as shown by the horizontal lines c. d. to some source of 
supply. A rheostat is needed to adjust the current strength 
until a suitable deflection of the needle is obtained between 
adjacent commutator segments. Now^ take two wires of 
the voltmeter and test the voltage between the various ad- 
jacent commutator segments. A reading will be obtained 
between each two segments on one side of the commutator, 
but on the side which contains the open coil no reading 
will be obtained until connection is made between the two 
segments to which the open coil is connected. At this 
point the voltmeter will show practically the full voltage of 
the supply current. 

885. How do you locate a short circuit? 

Ans. If the short circuit has come on while the arma- 
ture was in use, it will locate itself by a burned out coil. 
To test a new armature for short circuits we can proceed 
in the same way as for open circuit, the only difference 
being that, when we come to the short-circuited coil, we 
shall obtain either none, or at least a reduced deflection. 

886. What effect does an improper location of the 
brushes have? 

Ans, An improper location of the brushes will mani- 
fest itself by a more or less severe sparking. If the brushes 
are of the right dimensions the trouble can be remedied 
by simply shifting them to the proper location, which is that 
of least sparking. Brushes should be of such length, and 



Question's and Answers 1223 

set at such an angle^ that they come in contact with diamet- 
rically opposite points on the commutator^ with all bi-polar 
machines. 

887. How must the brushes be set in connection with 
multipolar machines ? 

Ans. This depends on the manner in which the armature 
is wound. With a la]^ winding there are as many brushes 
as there are pole pieces^ and they must be equally spaced 
around the periphery of the commutator. Provision must 
also be made so that they can be shifted to the point of least 
sparking. In wave wound armatures there may be only 
two brushes^ these being so spaced that they are separated 
by an angle equal to the angle of separation of two ad- 
jacent pole pieces; for instance^ with a four-pole field they 
would be separated by an angle of 90°. 

888. Is much shifting of the brushes necessary? 

Ans. This depends very much on the design of the ma- 
chine. With some of the older machines constant shifting 
of the brushes is required with changes in the load, but with 
the newer, and better machines this is reduced to a mini- 
mum. 

8S9. What is the ordinary size of a carbon brush? 

Ans. It should be of such size that not more than 25 
to 40 amperes per square inch of carbon are ever required 
to flow through it. 

890. How does inequality in field strength affect an ar- 
mature? 

Ans. Wherever this exists there will be more lines of 
force cut by the armature on one side than on the other, 
thus causing a higher potential to be generated on one side 
than on the other. The brushes will have to be set uneven 
distances apart around the commutator, and useless cur- 



1224 Steam Engineering 

rents will be set up in the armature windings, which will 
not only cause a loss of •power, but which will tend to over- 
heat the armature. 

SWITCHBOARDS. 

Switchboards are made up of panels of slate on a frame 
of angle iron. Each panel is designed for certain work so 
that a description of the different kinds of panels is suffi- 
cient. 

The first board to consider is the D. C. outgoing line 
board, served from D. C. generators. 

D. C. Generator Panels, 

Fig. 547 shows three generator panels, each of which is 
regularly equipped, from a capacity of 250 to 6,500 am- 
peres with 

1 Carbon break or magnetic blow-out circuit breaker, 
with telltale. 

1 Illuminated dial ammeter with shunt. 

1 Hand wheel and chain for operating rheostat. 

1 Eeceptacle for voltmeter plug 

1 S. P.-S. T. field switch.* 

1 S. P.-S. T. main switch. 

1 Eecording Watt-hour meter. 

A rear view of these panels is shown in Fig. 552. 



*S. T. means single throw. 

D. T. means double throw, i. e., the switch has two sets 
of clips and oan be thrown into either of them. 

S. P. means single pole. 

D. P. means double pole, i. e., opens both sides of circuit 

T. P. means triple pole, i. e., opens every conductor of 
a 3-phase system. 



Switch Boards 



1225 




Fig. 547 
d. c. generator panels 



1226 



Steam Engineering 




Fig. 548 
rear view of fig. 547 



Switch Boards 



1227 



The best practice puts a main switch at the machine, 
so that the cables from machines to board may be cut off 
f rSin generator. It is also good practice to run the equal- 
izer cable along in ducts from machine to machine without 
carrying it to the board. 

This equalizer connects the junctions of series field and 
brush on all machines as shown in Fig. 549 ; the shunt coils 
being omitted to simplify diagram. 

It is best to place the main switch and equalizer switch 
on a pedestal panel as shown in Fig. 550 for moderate ca- 




FiG. 549 

EQUALIZER 

pacity and in Fig. 551 for 4,000 ampere (and larger) ma- 
chines. The upper switch being the main switch. The 
rear view of these large capacity pedestals is shown in Fig. 
556. 

A better view of the 4,000 ampere toggle operated main 
switch is given in Fig. 553. The quick-break S. P.-S. T. 
switch is illustrated in Fig. 554. 

The field switch, Fig. 555, has a carbon break. Just 
before the switch opens it makes contact with an extra clip 
which puts a resistance on as a shunt around the field coils. 



1228 



Steam Engineering 




Fig. 5 5 0. 



Fig. 551 



Fig. 550 

pedestal panel for main and equalizer switches 

small capacity 

Fig. 551 
main and equalizer switches for large capacity 

If this were not done the fields would act like a kicking, 
or spark coil and their insulation be damaged. 

In Fig. 556 is seen the diagram of the panel shown in 
Figs. 557 and 558 when capacity is 800 K. W. or under. 



Switch Boards 



1229 




Fig. 552 

BEAR VIEW OF FIG. 551 



1230 



Steam Engineering 








H 


55 








1-1 


o 








f^ 


<i1 








en 


w 








( ) 


H 






o 












H 


i^ 


H 




<f 


U 




u* 




« 


< 


H 


o 




W 


H 


U 


:< 


CO 


s 


^ 


< 




>n 


O 


H 


J 


lO 


w 


U 




pq 


r^ 




^ 


U 


U 


1— ( 


8 


< 




s 




H 


^ 


!4 








<r; 


o 




W 


Q 


Q 


< 




a 


W 
H 

< 




^ 



o 






Switch Boards 



1231 



Fig. 557 shows the same panel when capacity is larger. 
The panel at left is for 1,000 and 1,200 K. W., the* next 
for 1,50,0 K. W. and over. The cuts on right side show the 
back and side view of the 1,500 K. W. panel. 





Type C form /< 
C/rcujt Breokisr 

Mo/nBus Bar 
TID /i/7)/r7€C er 
PoCe/7C/'a/BujPV/re Support -► 

A'/heo^Cat /iancf^v/jGG/ 

F/'e/cf Syv/tch (on, 
' Oenerotor Pone/ on/t/J 
Potent ia/ Peceptac/e 
Carcf /io/cfer 
Pheostat Cba/n \ 

Operc7t/np Mechan/sm] 
L/^/it/n^ Si/v/tc/y 
Type OB Pormy^ Stv/tch 



Pecorcfinj^ l^attmeter 
JVattmeter Pe>s /stance 

Fig. 556 
construction of fig. 547 for small capacity 



The scheme of electrical connections for panel of Pig, 
547 is shown in Pig. 558. 

B. C. Feeder Panels, 

A set of feeder panels for one feeder eacli is shown in 
Pigs. 559 and 560, a panel for two feeders with separate 
switches and one ammeter reading sum of both currents is 



1232 



Steam Engineering 





• Fig. 557 

CONSTRUCTION OF FIG. 547 FOR LARGE CAPACITY 



Switch Boards 



1233 



shown in Fig. 561, while Fig. 562 has an in&tmment and 
switch for each circuit. 

Fig. 563 gives the diagram of these feeder panels and 
Fig. 564 gives the electrical connections. 



Boc^ £//«M. 



_-X4nr 1 ^o Alarm &^/t 



fre5is>Lonce- 

jL. ignL /ng 3ivi tc h . 
ro Center Stacy H 
OfL/'gnting Si^it^h^ ' 
on acJjacenC Pane/ 



^Co L I'on L'gnts <^6 






I^OSitivQ Bus 

Equalizer Bus 




Fig. 558 
d. c. generator panels 



With panels as described the way to throw a generator 
in parallel with other generators already running, the fol- 
lowing procedure should be followed : 



1234 



Steam Engineering 




Fig. 559 
d. c. feeder panels 



Switch Boards 1235 

First — Close main and equalizer switches (on pedestal 
or panel near machine). 

Second — Close field switch (on panel). 

Third — Close circuit breaker. 

Fourth — Insert potential plug in receptacle and regulate 
voltage. 

Fifth — When the proper voltage is obtained^ close the 
other main switch (on panel). 

All the above applies to the distribution of the output of 
rotary converters^ but as they have some peculiarities they 
will be considered later. 

A. C, Generator Panel. 

The panel in Fig. 565 contains: 

1 Horizontal edgewise balanced three-phase indicating 
wattmeter, arranged for reading both the kilowatts output 
and the wattless component. 

1 Horizontal edgewise ammeter. 

1 Horizontal edgewise volt-meter. 

1 Balanced three-phase induction recording wattmeter. 

1 D. P. D. T. potential reversing switch for the indi- 
cating wattmeter. 

1 Four-point receptacle for synchronizing connections. 

1 Hand-wheel and chain operating mechanism for field 
rheostat. 

1 S. P. S. T. carbon break field switch with discharge 
clips. 

1 D. P. D. T. engine governor control switch. 

1 T. P. S. T. oil switch. 

1 Current transformer for instruments. 

2 Potential transformers for instruments. 

The functions of the instruments are to indicate the 
current, voltage and kilowatts output of the generator, and 
the wattless component of the output. For indicating the 



1236 



Steam Engineering 




Fig. 560 
rear view of fig. 559 



Switch Boards 1237 

wattless component, the potential coil of the indicating 
wattmeter is wired to the potential reversing switch, which 
is normally held by a spring so as to connect the instrument 
up as a wattmeter. By throwing the switch against the 
spring into the other position the potential coil is reversed, 
and the instrument reads the wattless compotent, giving a 
ready means of detecting any currents flowing between the 
alternators which are operating in parallel. 

The engine governor switch is to operate the motor which 
temporarily controls the governor on engine, or turbine 
when their speeds are being altered to bring two alternators 
into synchronism, or adjusting the division of load when 
operating in parallel. 

The generator oil switch has no automatic overload re- 
lease, as it is important to keep the generator in service dur- 
ing heavy short circuits caused by trouble on the transmis- 
sion lines. When such short circuits occur, the generators 
are immediately relieved by the opening of the automatic 
line switches. 

The diagrams for connecting up generator panels accord- 
ing as transformers are, or are not used will be found in 
Fi^s. 566 and 567. 

A. C, Outgoing Panel. — The panel on 'left of Fig. 568 
contains : 

13 Horizontal edgewise ammeters. 
1 T. P. S. T. oil switch, with overload release. 
3 Current transformers. 
Three ammeters — one for each phase — are furnished for 
each line, to facilitate the detection of unbalancing due to 
open circuits or leakage. With balanced loads, the amme- 
ter pointers should show equal deflections under normal 
conditions. As the ammeters are arranged in a perpendicu- 



I 



1238 



Steam Engineering 



Wm 



WM 



Fig. 561 
two feeder d. c. panel 



Fig. 562 
1,200 d. c. ampere, railway feeder panel for two circuits 



Switch Boards 



123S 



rr 

I N 

lL 



ea 1:2 ^ CDl 








U 



tSta U;IM •*«■ II--_DI I 



D 





Fig. 563 

OONSTRUCTION OF FIGS. 559 AND 562 



1240 



Steam Engineering 



^3 






r I 
U 



-^m-^ 



0<Q 



"3 

I- 



■sfiiflOr'^ 






Is 

QUI 



sSiSiSSlr' 



--Ql ? 



Hi"p 



~CH 



,>>4- 



i9 





rwN^J- 



Is 

•O (0 

r-O— *. 

I 

I 



I 
1 

4 



Fig. 564 
three styles of d. c. feeder pat^'els 



1241 






Fig. 565 
a. c. generator panel 

lar row any variation in the deflection of the pointers is 
readily detected. 

The current transformers serve to operate the ammeters 
and the automatic release on oil switches. 



1242 



Steam Engineering 






St^/tt/7eS/ 



P 



5-=m 




Ccfss S'otJierwiam asCaS^W* 
Coup/fnga- 



on O/V Syy/tC/7 

L 



% 



/?eceptac/e 
(C/qsec() 



s 



(E 



Green lo/np 
(Ojoen) 



n n>Sf6fi/e Bus 

Sw/tC/7 

fi heos tat I 



hi 



D/3C/jarffe 



^/terncfC/ng 
Cm r rent — 
Generator 



i 



3 Term /n a / ff/ocA 
on O/V 5>/^/ic/? 

/fes/sConce 



Vi>/6/r?eter- 
Bo/ance 3P/7arse 
'/fecorcf/rygiVatt/Tjeter 



Sync^ron/z//7pSuse9 



Tb/Trryerffency 
~V (Governor or7 7urb/ne 



0/75kv/'tch Operat/hff 
/Bases on fione/ 

^ =± 



Grootncf 3us r*-*! 

Poient/o/ IjJ 
Transformer 




/ncficat/n^ 
'\yattn7eter 

Td/^s/t/reJTxc/terJSuM 
rr/pCo// 

*^7b CmerQency 
Gotrtrnoron 7t>r6fn« 
■Ammeter' 

"Current 
TrctnsAormer 



7bPos/t/i/e 
£xc/6er/3us 



i 



^5tart/n9 
p|e| fiunn/nff 
5y/7c/?ron/A/r^ P/ugs 



Connect/ons for 
t/7e £np/ne Gok^ernor Contro/ A/otor 
ancf 3A^/tc/7 ty/?en Suyopf/ecf 



Bu3 



Fig. 566 
a. c. generator panel without step-up transformkk^ 



Switch Boards 1243 

The panel on right of Fig. 568 has but one ammeter and 
merely has the handle for operating the oil switch. The 
actual switch being in a brick compartment at rear of 
panel. The overload relay (3-pole) which trips the oil 
switch is at base of panel. 

Fig. 569 gives the electrical connections of panels in 
Fig. 568. 

The swinging bracket of Fig. 570 contains a synchro- 
nism indicator^ two lamps for synchronizing (practically 
a duplicate set of synchronizers) and a voltmeter for the 
station exciter generator.* 

To use the synchronism indicator put one plug in on 
panel of a generator which is runnings and the other plug 
in the panel of the generator which is starting. 

Fig. 571 shows a complete switchboard of one generator 
panel in center^ a panel for one outgoing line on the right, 
an exciter panel on left, with the swinging bracket on ex- 
treme left. 

Such a switchboard would be extended towards the right 
indefinitely^ as more lines were put on the station, by the 
addition of more outgoing line panels. 

Exciter Panel. — Each exciter panel is equipped with : 

1 Thomson feeder type ammeter. 

1 Hand-wheel for operating rheostat. 

1 Two-point potential receptacle connected to voltmeter. 

1 S. P. S. T. positive lever switch, with fuse mounted 
back of panel. 

One Exciter Panel in every switchboard is furnished 
with the following additional switches: (as in Fig. 572.) 



*D. C. Generator furnishing current for field of alter- 
nator. 



Casey^ 
^TG faiiB/ iA^/th Type ffbrnn ffj Swi tch 



f\/ormo//y in 
[lower C//ps 




Case S oCherty/se 03 Cose /f* 
^TG /=>ane/ ^vit/i 7y/>er/^rjrr7 /f.S 



CoUyO/Zn^ 



± /nd.'cot/np ^Vattnneter 



IPoj 



Wattmeter-^ 

3y/7c/?rt?n/'z/n^P/t/p$ 
5tort/ng/ 

V 



J9unn/ng 
Synchron/'z/np Buses 



Tdf^mer^ency 
Co\/ernor on Turbine 



y^_ 



/^6er)tfo/ 
fir ons formers 
fuse 



. . Grour7cf Bus 

-Transformer 



=0 



7bf=bs/d/V0 
£jrc/6erSu3 



VM-i 



fn 



i 



Tofbsftfi^e 
' fxc/terSu^ 
\Tr/pCo// 
Tbtmerperfc 
Coi^rnoro^' 



= 



EQ 



Current Transformer 



To Positive 
£'xc/terJSus 




IConnect/or>s for the £np/ne 
Governor Contra/ Motor 
ancf Sw/tch iy/7en Supp/Zecf 

/f/temating Current Generator 
^mmm-Bus 



ALTERNATING CURRENT GENERATOR PANEL FOR GEN^JIATOR WITH STEP4J|^ 
TRANSFORMER 

Fig. 567 
a. c. generator panel for generator with step-up 

TRANSFORMER 



Switch Boards 



1245 



rr^ 



Fig. 568 
a. c. outgoing line panels 



2 S. P. S. T. lever switches, with fuses back of panel, 
!for the control of station lighting and auxiliary circuits. 



1246 



Steam Engineering 



Case /9'/7rr/hrye/ 
w/th Type rfbr/n H3 5)^/tch 



3w/tche3 



5\y/tch — »| 
Ammeters 




Cose B ^otherwise asCa5e/f/9 Tf/^^nef 
with Type rfbrm /T 3w/tc/i 



fOpen) 
5w/tch- 



Over/oad 
/ ?e/ay 



Greer?/ia/r?p 
(C/osecf) 



Term/naJ d/ock 
on O/V^yv/tch 

^Current 
Transformer 



O// 5vy/tch operot/ng 
ffuses on Pane/ 




Ocft\po/ng l/ne 

I ? I ?1 9^'^^^^ JOetector9 



C/ho/rec 
Cb/'/s ' 



MO 

22© L/ghtn/ng 
rs o /Arresters 



\^ 



Fig. 569 
a. c. outgoing line panel 



Switch Boards 



1247 



On the frame of each exciter there are required the 
following switches^ mounted on a common slate base: 

1 S. P. S. T. negative lever switch. 

1 S. P. S. T. lever switch for equalizing. 

The exciter panels are designed single pole^ i. e,, only 
the positive leads of the generators are connected to the 
switch-board panels and only the positive bus-bar is mounted 
back of them. The negative and equalizer leads are con- 




FiG. 570 

SYNCHRONISM INDICATOR AND EXCITER VOLTMETER ON SWINGING 

BRACKET 



nected through their switches to the negative and equalizer 
bus-bars, which are placed under the floor near the exciters. 
With the bus-bars of opposite polarity so widely separated 
there is practically no chance of short circuit of the ex- 
citer connections. The positive field leads of the alternators 
are carried to the panels, while the negative field leads are 
permanently connected to the negative exciter bus-bar. 

Fig. 573 will give the electrical connections of an exciter 
panel. 



1248 



Steam Engineering 




Fig. 571 

MAIN STATION SWITCHBOARD FOR ONE A. C. GENERATOR AND ONE 
OUTGOING LINE 

The blower motors running the blowers which cool trans- 
formers are of the 3-phase induction type, or D. G. slnmt 
motors. 



Switch Boards 



1249 



• i i 



Fig. 



'oiZ 



EXCITER PANEL AUXILIARY LIGHTING SWITCHES ON SUB-BASE 

The D. C. motors are started by the regular starting box, 
Pig 574. 

The current to an induction motor is controlled by a 
switch like Fig. 575. if from auxiliary low voltage buses, 



1250 



Steam Engineering 



1- 



Vo/tmeter 

% 



fuse 



|l 

<) Q) 

^! 

it 

■5 



/i4<se' 



■--f 







To station „ \ 

l/^/?t3 . 

I 
I 
1 



I 

\ 

This ruse ancfSm'tch \ 
to/?eVZ/r/7/'s/7ecf *< 
^yCu-stomer T 

i 



J3us 



/e5'yo/tnC.Bu5es 
0/7 O/YSmtc/? 

/nstrunjQnt 
Cxc/t/r7^3u3 






% 



^StV/tc/7 

fuse 



0/75w/tc/7 
O/oercft/npBuses 
o/7f^/7e/ 



/?/7eostat 



Potent/a/ 
J8uses 

ffecGfitQc/ii 



(7b Genera 
ne/d ff/7eostat 



fxc/ter 



^ 



^Suse9 



Fig. 573 
exciter panel 



Switch Boards 1251 

or from an oil switch on a panel like Fig. 576, if full sta- 
tion voltage is used. 

The actual starting is done by a switch as in Fig. 577^ 
which is between secondaries of transformers or reactance 
coils and the induction motor. 

Fig. 578 shows connections of an induction motor to 
main buses^ using an oil switch and a starting switch. 





Fig. 574 



i<^ig. 575 



Fig. 574 

starting panel for d. c. blower set 

Fig. 575 

main switch panel for a. c. blower set 

The operation of several sub-stations on a single line is 
generally recognized as good practice. 

To insure continuity of service in the event of line 
trouble^ it is expedient to sectionalize the line at every sub- 



1252 



Steam Engineering 




Fig. 576 Fig. 577 

Fig. 576 

oil switch a. c. panel for incoming line 

motor driving exciter or a. c. side of rotary 

Fig. 577 
induction motor or rotary starting panel 



Switch Boards 1253 

station that is located at an intermediate point of the line. 
This sectionalizing is accomplished at each intermediate 
station by carrying the incoming line to the bus-bars 
through the air brake disconnecting switches which are in- 
stalled in connection with the arresters, and by carrying the 
outgoing line through an oil switch. In case of line trouble, 
this arrangement allows all sections of the line between the 
generating station, and any^ section on which the trouble 
occurs to be operated continuously. The power is auto- 
matically cut off from the section in trouble by an oil switch 
in the outgoing line panel equipment of the sub-station at 
the generating station end of the section, so that the air 
brake disconnecting switches in the sub-station at the other 
end of the section need never be opened under load. 

When duplicate transmission lines are used, two incom- 
ing Kne panels and two outgoing line panels are recom- 
mended for each intermediate sub-station. The installa- 
tion of these individual panels facilitates the disconnection 
of either line of any section and the continuance of the 
service over the other line of the section without any in- 
terruption. 

Arc Switchboards. — Fig. 579 shows a general view of the 
Thomson-Houston plug switchboard. A rear view of the 
same board is given in Fig. 580. 

In a standard panel the number of horizontal rows of 
holes equals one more than the number of generators. The 
vertical holes are always twice the number of generators. 
The positive leads of the generators are attached to the 
binding posts on the left-hand ends of the horizontal con- 
ductors. The negative leads are connected to the corre- 
sponding binding posts at the right-hand end of the board. 

The positive line wires are connected to the vertical straps 



1254 



Steam Engineering 



Case j<f " Caseff ot/^ermse as Co^e //* 

A TI /h/7e/ iv/th Type rrprm HjSwitch /fri fiane/vvith TyA?e r form H Switch 



/■ 
3* 



Mcftn 
Jdusez 



Sw/tches fff 



/fmmeter 






/i/Se^ 



Oi^er/oad 
/fe/ay 






^>£. 



5\^/tch 



^^/^t^ 



on O// 3w/tch 



m 



fCT 



Term/'na/B/oc/f on 
0//Syy/tc/7 



Current Trctnsformer 



J^ecflomp 
(C/osecfJ 



Greenlamp 
(OpenJ 0/f5v>/Jtch 

1 Operat/npBu^es 

on Pone/ 



Tr/p 
Co// 



^ * »AAA^ 



rAA/W-AA<^W^\AA^ 



Hp 



Afa/n T/^an^ former 



Svi/ftch 



/nc/uctton Motor 



Fig. 578 
induction motor panel 



Switch Boards 



1255 



on the left, and the negative wires to the similar straps on 
the right of the center panel. 

If a switchboard plug be inserted in any of the holes of 
the board, it puts the corresponding generator lead and the 
line wire in electrical connection, bnt as the positive line 
wires are back of the positive generator leads only, it is 




Fig. 579 



not possible to reverse the connection of the line and the 
generator accidentally, though any other combinations of 
lines and generators can be made readily and quickly. 

The holes of the lower horizontal rows have bushings 
connected with the vertical straps only. Plugs connected 
in pairs by flexible cable and inserted in the holes put the 
corresponding vertical straps in connection as needed, and 



^ 



1256 



Steam Engineering 



normally independent lines may be connected when one 
generator is required to supply several circuits. 

Lines and generator leads may be transferred^ while run- 
nings by the use of these cables^ without shutting down ma- 
chines or extinguishing lamps. 

The standard boards are arranged for an equal number 
of generators and circuits^ but special boards for any ratio 
of circuits to generators can be built. 




Fig. 580 



As it is sometimes convenient, even in small plants, to 
interchange lines and generators without shutting down 
machines, a special transfer cable with plugs has been de- 
vised. This serves the same purpose as the regular trans- 
fer cable, but the plugs may be used in any of the holes of 
the switchboard, as they are insulated, except at the tip, 
and when inserted connect with the line strips only. 

The transfer of circuits from one generator to another 
gives trouble to dynamo tenders who are not familiar with 
the operation of these plug switchboards. Fig. 581 illus- 







Switch Boards 










12f 


+ . 


1 

1 2 3 


A 

4 

-■ 


1 2 


3 


4 




! 


/'^ d 


) .O 

t o 


o •-^ 
o o < 




-e- 


-e- 


1 




2 


U < 


p 


\J 


L^ 


^ 1 




3 


o o o 


o o o 


o 


o 


1 

3 






o o o 


o o o 


o 


o 








B 














J ^ 4 


► o 

> 


/-\ d 


k /^ 


■\ r\ ^^ 






1 ' 


1 h' 4 


O O i 






^ 
/'-\ 


1 


1 


2 




^ - 


o 


<^ 


2 




3 


o c 


:> o 


o o o 


o 


o 


3 






O ( 


3 O 


o o o 


o 


o 








C 














[T 


o c 


i o 
? o 

5 O 


n < 


^ / 


N ^-\ ^^ 






1 ' 








1 




2 

3 


o o o 


u 
o 


u 
o 


2 
3 






o c 


5 O 


o o o 


o 


o 








D 












r 


> o 
) o 


O { 
O ( 


ri 


\ 


/-\ 


i^-\ 






1 






- CJ 


1 




2 


f 


u 


u 


2 




3 


O ( 


) o 


O ( 


) o 


o 


o 


3 




1 


o < 


> o 


o < 


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E 














C) c 


) o 
) o 
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O ( 

o c 
o c 


) ( 


> 


o 


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2 
3 


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M 

3 




• 


O i 


► o 


O i 


► o 


o 


o 












Fig. 581 















1258 



Steam Engineering 



trates the successive steps for transferring the lamps of 
two independent circuits from two generators to one with- 
out extinguishing the lamps on either circuit. 

This process is a very simple example of switchboard 
manipulation, but illustrates the method used for all com- 
binations. 




Fig. 582 



The location of plugs is shown by the black circles, which 
indicate that the corresponding bars of the horizontal and 
vertical rows are connected. 

Circuits No. 1 and No. 2, running independently from 
generators No. 1 and No. 2, respectively, are to be trans- 
ferred to run in series on generator No. 2. 

In A, Fig. 581, are two circuits running independently. 
In B the positive sides of both generators and circuits are 
connected by the insertion of additional plugs. 

At C both generators and circuits are in series. 



Switch Boards - 1259 

Next insert plugs and cables as shown in D. Then 
v:ithdraw plugs on row corresponding ta generator No. 1, 
and the circuits No. 1 and No. 2 are in series on machine 
No. 2, and machine No. 1 is disconnected as at E. 

Similar transfers can be made between any two circuits 
or machines, and by a continuation of the process additional 
circuits can be thrown in the same machine. The transfer 
of the two circuits to independent generators is accom- 
plished by reversing the process illustrated. 

Pig. 582 shows the wiring and connections of the West- 
ern Electric Co.^s series arc switchboard. At the top of 
the board are mounted six ammeters, one being connected 
in the circuit of each machine. On the lower part of the 
board are a number of holes, under which, on the back of 
the board, are mounted spring jacks to which the circuit 
and machine terminals are connected. For making con- 
nections between dynamos and circuits, flexible cables ter- 
minating at each end in a plug, are used; these are com- 
monly called "jumpers.^^ The board shown has a capacity 
of six machines and nine circuits, and with the connec- 
tions as shown, machine 1 is furnishing current to circuit 1, 
machine 2 is furnishing current to circuits 2 and 3, and 
machine 4 is furnishing current to circuits 4, 5 and 7. In 
connecting together arc dynamos and circuits the positive 
of the machine (or that terminal from which the current 
is flowing) is connected to the positive of the circuit (the 
terminal into which the current is flowing). Likewise the 
negative of the machine is connected to the negative of the 
circuit. Where more than one circuit is to be operated from 
one dynamo, the negative of the first circuit is connected 
to the positive of the second. At each side of the name plate 
(at 3, for instance) there are three holes. The large hole 
is used for the permanent connection, while the smaller 



1260 Steam Engineering 

holes are used for transferring circuits, without shutting 
down the dynamo. Smaller cables and plugs are used for 
transferring. If it is desired to cut off circuit 5 from 
machine 4, a plug is inserted in one of the small holes at 
the right of 4, the other plug being inserted in one of the 
holes at the left of 7. Circuit 5 would now be short-cir> 
cuited, and the plug in the + of 5 can now be transferred 
to the permanent connection in the + of ^^ ^^^ the cords 
running to 5 removed. If it is desired to cut in a circuit, 
say circuit 6 onto machine 2, insert a cord between the — of 
circuit 2 and the + of 6 and another between the — of 6 
and the + of 3. Now pull the plug on the cord connect- 
ing the — of 2 and the + of 3 and insert the permanent 
connections. In cutting in circuits, if they contain a great 
number of lights, a long arc may be drawn when the plug 
between 2 and 3 is pulled, and it is sometimes advisable to 
shut down the machine when making a change of this kind. 

TRANSFORMERS. 

When a current passes through a conductor it creates 
around it a field of force. If a second wire, qr conductor 
lies parallel to the first during the time that the field of 
force is being built up, electromotive force will be impressed 
upon it, and will be of such polarity that the current pro- 
duced by it will be in a direction opposite to the direction 
of the original current. The transformer contains two 
coils of wire insulated from each other. 

In Fig. 583 is shown the principle upon which the trans- 
former used in alternating current work operates. Two 
separate coils of wire are wound on a ring of laminated 
iron. One of the coils contains a number of turns of fine 
wire, while the other contains only a few turns of large 



Transformers 1261 

wire. When an alternating current is sent around the coils 
of fine wire^ generally called the primary^ a current will be 
induced in the coil of heavy wire, or secondary. The amount 
of current induced in the larger wire will be relatively 
greater in amperes, and less in potential than that of the 
fine wire circuit. This ratio is almost entirely dependent 
upon the relative number of turns existing between the 
large and the small wires. To illustrate, suppose we had 
a current of 10 amperes at a pressure of 1,000 volts in the 




Fig. 583 

primary, and there were ten times as many turns of wire 
in the primary coil as in the secondary, then we would get 
a current of 100 amperes at a pressure of 100 volts in the 
secondary coil. This same relation would hold true what- 
ever the ratio between the number of turns on tlie two 
coils might be. In Fig. 584 is shown a core of iron hav- 
ing on one end a primary coil connected to a battery. On 
the other end of the core is another coil connected to the 
ends of which is an incandescent lamp. By making and 
breaking the battery circuit the lamp may be made to flash 



1262 



Steam Engineering 



up, due to the great voltage induced in the secondary coil. 
This is a good thing to remember when working with a 
dynamo or motor. Do not quickly break the shunt field 
connection, as the increased voltage due to the current in- 




Fig. 584 



duced by the field magnet when the circuit is broken is 
liable to puncture the insulation and necessitate the re- 
winding of the field coil. 

Referring to Fig. 585, A represents the alternator, B its 
brushes and D and E the mains to the transformer H. This 





Fig. 585 
diagram of alternator, line, transformer, and secondary 

CIRCUIT 

transformer consists of a core of iron C on which are two 
windings. The coil P is called the primary, and is con- 
nected to the main from alternator. The other coil S is 
called the secondary, and to it the load is connected. 



Transformers 



1263 






Fig. 586 
transformer coils in wound, bound and taped stages of 
completion 



1264 . 



Steam Engineering 



Whatever the voltage of alternator A^ that of the sec- 
ondary circuit F. L. G. will be three-eighths of it because 
there are eight turns on the primary and three turns on the 
secondary. The power in the secondary circuit is practi- 
cally the same (minus the losses) as is given out by the al- 
ternator^ hence the primary current is low and wire is small. 
The secondary current is large and the wire is large. 

Since one kilowatt can be a combination of a large cur- 
rent and small pressure, or small current and large pres- 




FiG. 587 

COILS, AIR DUCTS AND SEPARATORS FOR TRANSFORMER 



■sure, it is evident that the transformer simply transfers the 
power, and transforms the voltage, and indirectly the cur- 
rent.' 

This transformer (Fig. 585) lowers the voltage and is 
called a step down transformer. 

When the secondary is connected to the alternator, the 
transformer raises the voltage and is called a step up trans- 
former. 

The coils of a transformer must be very well insulated. 
After winding they are bound, to keep them in shape, and 



Transformers 1265 

then wound with linen tape, or varnished cambric cloth. 
Fig. 586 shows a coil in the three stages of completion. 

In Fig. 587 is shown a set of completed coils, together 
with the ventilating ducts and mica barriers sufficient for 
one leg of a transformer. 

Fig. 588 shows the two legs of a transformer, which form 
its iron core, each over half filled with coils. The coil is 
made of sheets of soft iron. 

Fig. 589 shows the manner in which the coils are some- 
times bound up to be placed in transformer as one coil. 

Exciting Current. — The Exciting Current, being also 
called by various other names, such as leakage current, open 
circuit current, and magnetizing current, is a very impor- 
tant factor. 

In order that a transformer may be ready to do its work 
it is always connected to the line. This means that the 
primary coil is always magnetizing the core, if no current 
is drawn from the secondary. 

This steady flow of current to excite the primary is the 
price we have to pay for having the transformer continually 
ready for service. ' 

A transformer should therefore never be left on a line 
unless it is needed. 

Efficiency of Transformers. — The losses in transformers 
are less than any other piece of electrical machinery or ap- 
paratus; 98 per cent of the intake being delivered in the 
larger sizes as used in railroad sub-stations or power houses, 
when fully loaded. Unfortunately they lose about the same 
amount of power at all loads. 

A. 100 K. W. transformer loses 2 K. W. at full load, its 
efficiency is then 98-f-100=0.98. At half load it loses 
2 K. W., but is only carrying 50 K. W., so (its losses are 



^^^^'-^^^S^^^^Vf^sffPH 




Fig. 588 
interior construction of an air blast transformer 




Fig. 589 

SET OF COILS MADE UP READY TO BE PLACED IN TRANSFOBMEB 



Transformers 



1267 



now equivalent to 4 K. W. on a 100 K. W.) its efHciency 
is 484-50=0.96. 




Fig. 590 
air blast transformer 

At quarter load it takes in 25 K. W., loses 2 K. W., so 
its efficiency is 23-^25=0.92. 

By clever designing transformers are built to be most 
efficient at three-quarters load. They are a little less effi- 



1268 Steam Engineering 

cient at half, and full loads, and still less at quarter load, 
and quarter overload, but never fall below 95 per cent. 

Cooling Transformers. — Small transformers hung up on 
poles are cooled by surface radiation only. 

Medium sized ones are filled with oil. This conducts the 
lieat to the iron case, and also acts as an insulator. 

The oil will also flow in and fill a break in the cloth, or 
mica after a puncture. 

Air Hast avoids the danger of oil in case of fire or flame 
•due to short circuits. They are cheap as a transformer may 
be much more heavily loaded when cooled by the air blast, 
:and the blower only consumes 1-10 of 1 per cent of the full 
load output of transformer. 

Fig. 590 shows the interior construction of an air blast 
"transformer and Fig. 591 shows how they are installed. 

Water cooled. These are the smallest and cheapest trans- 
formers to build, but not so cheap to run as is the air blast. 

The cases are filled with oil which absorbs heat from coils. 
Pipes are run through the oil, in which cold water is cir- 
<julated. 

In a water power plant where the head of water would 
render pumps unnecessary the water cooled type would cer- 
tainly be the best. 

Auto-Transformers. — These are only applicable to cer- 
tain cases. 

The idea is shown in Fig. 592. The same coil of wire 
A to B is used as primary and secondary, the whole being 
the primary, and portions as C to D, D to E, or C to E 
being used as secondary. 

They are only used where the primary voltage is fairly 
low and the secondary voltage is not less than one-fifth of 
the primary voltage. 




CO 

'^ 

o 

« 
H 

H 

h-t 

o 

o 

M 






1270 Steam Engineering 

They are used instead of resistances to start A. C. motors. 

Allis- Chalmers Power Transformers. — Transformers for 
use on power transmission lines are made by Allis-Chalmers' 
Company in three different types, depending on the method 
used for cooling. These types are as follows : oil-filled self- 
cooled (0. F. S. C.) ; oil-filled water-cooled (0. P. W. C.) 
and air-blast. In the fir§t the heat is carried off by radia- 
tion, and conduction from the case; in the second by the 
circulation of water through coiled pipes immersed in the 
oil; and in the third by currents of air forced through the 




B E 

Fig. 592 

DIAGRAM OF AUTO-TRANSFORMER OR COMPENSATOR 

transformer. Oil-insulated transformers are used in the 
great majority of cases, and the question as to whether they 
shall be self-cooled or water-cooled is determined largely by 
the size of the units, and the available supply of cooling 
water. 

Self-cooled transformers are built in sizes up to 250 K. 
V. A. (kilo volt- amperes). Above this size the external 
surface of the case is not sufficient for the effective radia- j 
tion of the heat unless the case is made abnormally large. 
Fig. 593 shows a standard transformer of this type. 

Water-cooled transformers, Fig. 594, are made in sizes 
from 100 K. V. A. up. Water is circulated through a coil 
of seainless copper tubing immersed in the oil in the upper 



Transformers 



1271 



part of the tank^ and the heat is effectivel}^ carried off. 
Wherever water is available and not expensive this method 
is preferable to air coolings even for comparatively small 




Fig. 593 

ALUS-CHALMERS OIL-FILLED SELF-COOLED TRANSFORMER, 60 CYCLE, 

170 K. w., 20,000 TO 2,300 volts 

transformers, as it permits operation at lower temperatures, 
and allows more margin for overloads. 

Air-blast transformers are made in sizes from 75 K. V. 
A. up. Cooling is effected by placing the transformer over 




Fig. 594 

allis-chalmers oil-filled water-cooled transformeb, 25 cycle, 

500 K. w., 20,000 TO 375 volts 



Transformers 1273 

an air chamber in which a pressure of air is maintained 
by motor driven fans; currents of air passing up around the 
transformer carry off the heat. In this type oil cannot be 
used for insulating purposes, and 25,000 volts is the high- 
est pressure for which it is advisable to build them. 

Much has been written about the relative fire risks of 
air-blast and oil-filled transformers, but this is a matter 
that depends as much on surrounding conditions, and the 
location of the transformers as upon the construction. The 
air-blast transformer contains a small quantity of inflam- 
mable matter as compared with the oil-filled transformer, 
but this material is much more easily ignited. A break- 
down in an air-blast transformer is usually followed by 
an electric arc that sets fire to the insulating materials, and 
the flame soon spreads under the action of the forced cir- 
culation of air. Although the fire is of comparatively short 
duration, it is quite capable of ignitng the building unless 
everything near the transformers is of fire-proof construc- 
tion. 

The chance of an oil-filled transformer catching fire on 
account of any short circuit in the windings is extremely 
small, because oil will burn only in the presence of oxygen, 
and, since the transformer is completely submerged in oil, 
no air can get at it. Moreover, the oil used in transfor- 
mers is not easily ignited ; it will not burn in open air un- 
less its temperature is first raised to about 400° F. In 
fact, the chief danger of fire is not that the oil may be 
ignited by any defect or arc within the transformer,' but 
that a fire in the building in which the transformers are 
installed may so heat the oil as to cause it to take fire. 

General construction.— "The general construction of the 
coils and core is much the same in all three types, regard- 
less of the method of cooling. All transformer coils are 



1274 



Steam Engineering 




Fig. 595 

PARTLY ASSEMBLED 25 CYCLE, 500 K. W., 20,000 TO 375 VOLT 
TRANSFORMER 



Transformers 



1275 




Fig. 596 

GORE AND COILS, 500 K. W.. 20,000 TO 875 VOLT TRANSFORMERS 



1276 



Steam Engineering 



woTind with double cotton covered strip copper^ one turn 
per layer^ with fuUerboard insulation^ in addition to the 
cotton covering, between turns. Exceptions to this con- 




FiG. 597 

struction are made only when the size of the conductor is 
such as to render the use of copper strip impracticable, and 
in such cases the coils are wound with round, double-cotton 



Transformers 1277 

covered wire with few turns per layer, so that the voltage 
between the layers is kept within safe limit J. The core is 
built up of steel sheets 0.0014 inch thick. In the larger 
sizes, space blocks are placed every few inches in the core, 
thus providing ducts through which oil can circulate and 
carry off the heat. Also, in assembling the coils, spaces are 
formed between the coil sections, and between the coils and 
core, so that all parts are in contact with a free circulation 
of oil. Fig. 595 shows a core partly built up and Fig. 596 
core and coils completely assembled. Fig. 597 shows the 
windings and cor^ for a transformer of smaller output. 

ROTARY CONVERTERS. 

Perhaps one of the greatest objections to the use of direct 
current is the inability to change its voltage without the 
use of moving machinery. 

There is but one way to transform direct current and that 
is by a motor and generator. 

This motor-generator set usually consists of a direct cur- 
rent motor driven by current at the pressure of the incom- 
ing line. This motor drives a direct current generator 
which furnishes current at the desired pressure. 

By altering the strength of the field of the generator we 
regulate the outgoing pressure to suit the requirements. 

The motor and generator are built on the same shaft, 
and set on a long cast iron base, making them mechanically 
i one machine. 

When the incoming and outgoing voltages can have the 
same ratio to each other always, a cheaper form of ma- 
chine can be used called a Dynamotor. 

This is a direct current motor running on the incoming 
voltages. On the same armature core is a separate winding 
connected to its own commutator at the other end of arma- 



1278 



Steam Engineering 



ture. The one set of field magnets serves for the motor 
winding and the generator or dynamo winding. 

The Rotary Converter. — Combines in a single machine 
the functions of the two machines jnst described. In one 
sense it may be regarded as an alternating-current syn- 
chronous motor driving a direct-current generator^ or if 




*^"-"-«.ifi^ 



Fig. 598 

WESTINGHOUSE 1,500 K. W. ROTAR:*: CONVERTER 

the machine be inverted^ it may be considered a direct-cur- 
rent motor^ driving an alternating-current generator. 

As direct current cannot readily be generated at, or trans- 
formed to a high voltage, which economical distribution dic- 
tates, alternating current is almost invariably used for all 
except very small electrical power transmissions. Wherever 



Rotary Converters 



1279 



direct current is used^ as in direct current railway lines^ the 
alternating current must be transformed into direct cur- 
rent. While^ of course^ this can be accomplished by means 
of a motor-generator set, consisting of an alternating cur- 
rent motor connected to a direct current generator^, the 




Fig. 599 

WESTINGHOUSE 300 K. W. ROTARY CONVERTER, COO D. C. VOLTS, 500 
D. C. AMPERES, THREE-PHASE, 60 CYCLES 



higher efficiency and lower cost of the rotary converter ac- 
counts for tlie ahnost universal practice of using it in pref- 
erence to the motor-generator on low frequencies. 

Eotary converters have many of the features which dis- 
tinguish the most modern direct-current machines; the 



1280 



Steam Engineering 



only material difference being the addition of collector 
rings connected to certain points of the armature winding. 
The number of such connections depends upon the number 
of poles and phases. 

The machine is built for single-phase^ two-phase^, three- 
phase or six-phase circuits^ although single-phase and six- 
phase converters are seldom desired. A two phase con- 
verter is provided with four collecting rings, and a three- 




FiG. 600 

WESTINGHOUSE ROTARY CONVERTER ARMATURE FROM THE COLLECTOB 
SIDE, 300 K. W., 550 VOLTS, THREE-PHASE 



phase converter is provided wth three collecting rings. As 
it is usually found expedient to transmit the alternating 
current at high pressure^ transformers must be employed 
for lowering the potential to secure the proper direct volt- 
age. Where the converter is operated from direct^ to alter- 
nating current^ transformers are usually employed to raise 
the voltage for transmission. 

A rotary converter may be separately excited, but it is 
■usually shunt wound, or compound wound, depending upon 



Rotary Converters ' 1281 

the nature of the service. When the load is variable, as in 
railway service, the machine is compound wound, which 
tends to maintain the direct current voltage constant, by 
compensating for the drop in the supply 'circuit as the load 
comes on. The ratio between the alternating and direct 
current voltages of a rotary converter depends upon the 
number of phases, upon the wave form of its alternating 
current, upon the lead given to the direct current brushes, 
and to a slight extent upon the field excitation. In any 
given converter, therefore, the direct current voltage de- 
pends practically upon the voltage of the alternating cur- 
rent applied. To a smaller extent it depends upon the 
armature drop, which diminishes the voltage ratio in slight 
proportion with the load when running A. C. to D. C. and 
increases the ratio when running D. C. to A. C. This will 
be easily seen by referring to a saturation curve. 

With a sine wave the ratios of conversion are approxi- 
mately as follows : 
Single Phase, Two Phase, Three Phase, Six Phase, 

.71 .71 .61 .71 or .61 

Thus if the D. C. voltage be 550 volts, the A. C, if two- 
phase, will be .71X550=390 volts, and if three-phase, it 
will be .61X550=335 volts. The ratio of conversion in 
the six-phase is .71 with the star connection, or .61 with 
the double delta connection. 

The variations from these figures with wave forms in 
commercial use are taken into account in the ratios of the 
transformers used in connection with the rotary converters. 

The rotary converter built by the Westinghouse Com- 
pany presents in its frame the same mechanical features as 
are found in its well-known line of direct current machines. 
The machine is of the multipolar type, havng laminated 
steel poles, cast, or bolted to its iron yoke, and carrying 



1282 Steam Engineering 

easily removable field coils. If the windings are compound^ 
the serieS;, and shunt coils are insulated separately. The 
armature is of the slotted drum type^ with either a two cir- 
cuity or multiple tj^e of winding. The number of poles in 
a rotary converter is dependent upon the speed of the ar- 
mature and the frequency^ as is the case with all alternating 
current machinery. 

This feature accounts for the difficulty in designing ro- 
tary converters for high frequencies^ as the maximum arma- 




FiG. 601 

WESTINGHOUSE COMPLETE ROTARY CONVERTER ARMATURE FROM THE 
COMMUTATOR SIDE, 300 K. W., 550 VOLTS, THREE-PHASE 

ture speed is limited by the maximum safe speed of the 
periphery of armature and commutator. With a given 
speedy however^ the number of poles is proportional to the 
frequency, and with a given maximum speed of armature 
and commutator peripher}^, the distance between adjacent 
poles, and therefore adjacent brush holders, is inversely 
proportional to the frequency. With high voltage 60-cycle 
converters, these facts necessitate high commutator speeds, 
short distances between poles, and between brush holders. 



Rotary Converters 1283 

narrow commutator segments^ and a high voltage between 
adjacent segments; resulting in a tendency to flashing over 
between brushes at sudden overload. 

This should always be borne in mind when choo^g the 
frequency of a system on which rotary converters are to be 
used^ and it applies particularly to 500 and 600 volt rail- 
way rotary converters^ which are required to withstand 
much more severe service than is ever experienced on light- 
ing systems. 

In the erection of a rotary converter the following con- 
siderations should^ as far as possible^ be observed: 

First. It should not be located in a position where it 
would be exposed to moisture^ as drippings from pipes^ or 
escaping steam. 

Second. It should not be exposed to dirt or dust^ espe- 
cially from coal. 

Third. It should be located in as cool and well venti- 
lated a place as possible. The temperature of the machine 
depends upon the temperature of the air surrounding it. 

Fourth. It should be so located as to allow easy access 
to the alternating current brushes^ and also to the com- 
mutator. These are the parts requiring special attention. 
Eotary converters should be set on substantial foundations 
in order to prevent vibration when running. 

The following list of instructions refer more particularly 
to Westinghouse machines;, but much of it will apply to 
others. 

Insulation of Frame. — Whether the frame should be in- 
sulated from the ground is a matter to be determined by the 
engineer in charge of the plant^, but rotary converters are 
usually not insulated. However, the following remarks 
which apply to alternating practice, may not be amiss : Gen- 
erally speaking, the strain on the insulation of the windings 



1284 Steam Engineering 

will be decreased, and the danger to the attendant increased 
by insulating the frame. When, however, it is considered 
advisable to insulate the frame, the foundation should be 
capped with a strong wooden frame bolted down. The bolts 
which hold this frame to the masonry should not come in 
contact with those which hold the machine to the frame, 
nor should any metal, or electrical conductor unite the two 
sets of bolts. 

The wooden insulating frame under the machine may 
also be covered with some insulating waterproof paint or 
compound. 

Erection of Machine, — When placing the parts of a ma- 
chine in position the following points should be observed: 

(1) Set the lower half of the field in position and place 
the armature in its bearings, having first carefully examined 
the bearings and oil wells to be sure that they are clean and 
free from dirt. Be sure that the oil rings are in place and 
in good running order. 

(2) Clean the contact surfaces of both halves of the 
field and file off the burs,, if any exist, to secure perfect 
magnetic joints at the division of the yoke. 

(3) Set the upper half of the field in position and 
secure it to the lower half by means of the field bolts and 
feather keys. 

(4) Note that the machine is to be perfectly level along 
the axis of the shaft, except that when an oscillator is at- 
tached the machine is placed slightly out of level, as will 
be pointed out later. 

Armature, — Never try to support any of the weight of 
an armature by the commutator or collector rings. Do not 
allow these parts to rest on any blocking, and do not pass 
a rope around, them for the purpose of lifting. When hand- 
ling the armature always support it with a rope slung 



Rotary Converters 1285 

about the shafts and be careful not to mar or scratch the 
shaft, as any roughness would cause it to cut the bearings 
and so produce heating when the machine is running. 

In putting the armature in the field be careful not to 
scratch the bearings, nor to bend the oil rings. 

Coils. Assembly or field coils. — The field coils of the 
larger machines are shipped separately. The coils are held 
on the poles by the dampers, which should be bolted to the 
pole pieces. The coils on each of the separate halves of the 
field should be properly connected before the machine is 
set up. 

Each pole piece has a number stamped with steel stencil 
and also painted in red, and a red line is drawn parallel 
and near to one edge of the pole. This line and number 
correspond to similar marks inside the coil. In erecting, 
place the coils on the poles so that the marks coincide. 

If a rotary converter has been exposed to dampness it 
may be dried out by employing one of the following meth- 
ods: 

(1) Short-circuit the field and apply to the collecting 
rings about 10 per cent of normal alternating current volt- 
age, which may usually be obtained from the lowering 
transformers. During this application the D. C. brushes 
must be raised and the rotary must be at a standstill. The 
standard Westinghouse transformers are usually provided 
with taps, between which a low voltage may be obtained. 

(2) Eun the rotary converter, driving it by a suitable 
motor, and short-circuit the armature on the direct cur- 
rent side with very weak field excitation. If shunt woimd, 
separate excitation at very low voltage must be used. If 
the converter be compound wound, the armature may be 
short-circuited through the series field coils. As rotary con- 
verters are usually very sensitive as series machines this 



1286 Steam Engineering 

method should be undertaken only by those who are thor- 
oughly experienced, as there is danger of excessive current. 

(3) Dry the field coils from a source of separate excita- 
tion, with about two- thirds of the normal D. C. voltage. 
This will also dry the armature somewhat. While drying 
out, the temperature of the accessible parts should be 
watched closely, and not be allowed to exceed 75° C. 

In drying out with current there is always danger of 
overheating the windings, as the inner parts may get in- 
jurously hot because they cannot quickly dissipate the heat 
generated in them. Coils containing moisture are more 
easily injured by overheating than those which are already 
dry. Several hours, or even days, may be required for 
thoroughly drying out. 

Repairs to Armatures. — The instructions pertaining to 
armature troubles, and repairs to commutators and other 
parts of electric generators, will also apply in the case of 
rotary converters. 

Bucking. — Bucking is the expressive name given to the 
action of the rotary converter when arcing occurs between 
two adjacent brush holder arms, thereby short-circuiting 
the machine. Bucking is, in general, due to abnormally 
high voltage, or a path of low resistance over the commu- 
tator surface, or to abnormal commutation conditions. The 
poorer the commutation, the more liable will the machine 
be to buck whenever these abnormal operating conditions 
occur. Some of the particular causes for bucking are the 
following : 

a) Eough or dirty commutator. A drop of water fall- 
ing on the commutator has been known to cause the ma- 
chine to buck. 

(b) Excessive voltage due to increase in A. C. voltage. 



Rotarij Converters 1287 

(c) Excessive voltage due to static disturbances from 
lightning arrester short-circuits. 

(d) Excessive voltage due to static discharge from or 
through lowering transformers. When bucking is due to 
this cause^ it will usually occur when switching is done in 
'the high tension circuits. 

(e) Bucking may be caused by fluctuations in the volt- 
age, due to the removal of a short-circuit. 

In multiple wound rotary converters, balancing rings or 
cross-connections are employed as in direct current gener- 
ators. These rings connect together points of equal poten- 
tial around the commutator. 

By this means the same field strength is obtained under 
each pole. 

Oscillators. — The armature of a rotary converter re- 
volving with its horizontal shaft will take up normally a 
fixed position relative to its bearings, and the frame of 
the machine, and revolve without any tendency to move 
or oscillate in the direction of its length. This is detri- 
mental to its best operation as the brushes are liable to wear 
grooves in the commutator, and collector. It therefore be- 
comes necessary to provide a means of producing a periodic 
movement of the armature in the direction of its length, and 
this function is performed by the oscillator. 

There are two classes of oscillators, viz. : mechanical and 
magnetic. The mechanical oscillator employed by the West- 
inghouse Co. is described as follows : 

This device is self-contained' and is carried over one end 

I of the shaft. The operating part consists of a steel plate 

grooved by a circular ball race in which travels a hardened 

steel ball. The steel plate is not quite parallel to the face 

of the end of the shaft. The normal position of the ball is 



1288 Steam Engineering 

at the lowest point of the circular race. The steel plate is 
backed by a spring. 

The machine is leveled so that the armature is slightly 
inclined toward the oscillator. The steel plate is then ad- 
justed so that when the ball is at its bottom position it just 
comes in contact with the shaft end. As the armature re- 
volves the ball is carried up the race, and owing to the 

Magnetic Oscillators ^^ ^oW»9^ 






V: 







M 



laterrupter 

Fig. 602 
diagram of connections for magnetic oscillator 

inclination of this race, compresses the spring. The reaction 
of the spring drives the shaft away. Thus the armature re- 
ceives an impulse, which moves it t6ward the other limit 
of its travel, and it continues to move until the opposing 
forces bring it to rest and start it back to its normal posi- 
tion, where it again comes in contact with the ball, and the 
operation begins over again. Fig. 602 shows a diagram- 
matic view of the Westinghouse magnetic oscillator, of which 



Rotary Converters 1289 

the following is a description. A magnet is mounted upon 
one of the bearing housings of the rotary converter in such 
a manner as to attract the end of the shaft. When the cir- 
cuit is closed the magnet draws the shaft toward it and 
when the circuit opens^ the armature tends to resume its 
normal position which is determined by the leveling of the 
converter. The magnet has in series with it a make and 
break device called an interrupter which is controlled by a 
dash-pot to secure the proper frequency of action. 

As the dash-pot offers an adjustable resistance^ the fre- 
quency of the impulses is adjustible. When there are a num- 
ber of rotary converters in the same sub-station, the magnetic 
oscillators are connected in series, and controlled by a single 
interrupter. 

Under certain conditions the commutator, and collector 
surfaces of machines provided with oscillators may be worn 
in irregular wavy grooves. 

When this occurs it will then be necessary to turn down 
the commutator and collector. 

QUESTIONS AND ANSWERS. 

891. What is the function of a transformer? 

Ans, To transform the current from a higher, to a lower 
voltage, or vice-versa. 

892. What principles govern the action of a trans- 
former? 

Ans. The principles of electro-magnetic induction. 

893. What is a step up transformer? 
Ans, A transformer that raises the voltage. 

894. What is a step down transformer ? 
Ans, One that lowers the voltage. 

895. How are transformers cooled? 



1290 Steam Engineering 

Ans. Small sizes by surface radiation. Larger sizes by 
oil ; also by air blast. Some of the smaller sizes are cooled 
by water circulating through surrounding coils. 

896. How is direct current transformed from one volt- 
age to another ? 

Ans. By means of a machine called a motor-generator. 

897. Describe in brief a motor-generator. 

Ans. It consists usually of a D. C. motor driven by 
current at the voltage of the incoming line. This motor in 
turn drives a D. C. generator that furnishes current at the 
desired voltage. 

898. How is the outgoing voltage regulated? 

Ans. By altering the field strength of the generator. 

899. In case the incoming and outgoing current can bear 
the same ratio to each other constantly^ what kind of an 
apparatus is used ? 

Ans. A machine called a dynamotor. 

900. Describe the operation of a dynamotor. 

Ans. It is a D. C. motor running on the incoming volt- 
ages. On the same armature core is a separate winding 
connected to its own commutator at the other end of the 
armature. One set of field magnets serves for the motor 
winding and the generator or dynamo winding. 

901. Describe in general terms a rotary converter. 

Ans. It combines in a single machine the functions of 
a motor-generator^ and a dynamotor. 

902. Why are rotary converters and transformers neces- 
sary ? 

Ans. Because it is more economical to transmit alter- 
nating current at high voltages and transform^ or convert 
it to the lower voltage at which it is used. 

903. Give another reason for using rotary converters. 



Questions and Ansivers 1291 

Ans. For the purpose of transforming alternating cur- 
rent into direct current when direct current is used. 

904. What is the chief point of difference between a 
rotary converter and a direct current generator? 

Ans. The rotary has collector rings connected to certain 
points of the armature winding. f 

905. What governs the number of such connections? 
Ans. The number of poles and phases. 

906. Describe the different types of rotaries. 

Ans. They are built for single-phase^ two-phase^ three- 
phase or six-phase. 

907. How many collecting rings has a two-phase con- 
verter? 

Ans. Four collecting rings. 

908. How many collecting rings has a three-phase con- 
verter ? 

Ans. Three collecting rings. 

909. When alternating current is transmitted at high 
pressure^ what means are employed for lowering the po- 
tential ? 

Ans. Transformers. 

910. When the incoming current is direct and the out- 
going current alternating^ how is the voltage raised ? 

Ans. By step up transformers. 

911. Describe the winding of a rotary converter. 

Ans. It is usually shunt wound^ or compound wound^ 
although sometimes separately excited. * 

912. How are rotaries in railway service usually wound ? 
Ans. Compound;, owing to variations in the load. 

913. What advantage is gained by this method of wind- 
ing? 

Ans. It tends to maintain the D. C. voltage constant. 



1292 Steam Engineering 

914. Upon what does the ratio between the A. C. and 
D. C. voltages of a rotary depend ? 

Ans. Upon the number of phases^ the lead given the 
D. C. brushes, the wave form of its alternating current, 
and upon the field excitation. 

915. Does the armature drop affect this ratio to any 
extent ? 

Ans. It does by decreasing it slightly when running 
A. C. to D. C. and increasing it when running D. C. to 
A. C. 

916. What are the ratios of conversion approximately? 
Ans. Single-phase 71 

Two-phase 71 

Three-phase 61 

Six-phase 71 or .61 

917. Give an example illustrating above. 

Ans. If D. C. voltage is 550 volts, the A. C, if two- 
phase will be 500 X. 71=390 volts, or if three-phase it will 
be 550X.61=335 volts. 

918. What precautions should be observed in the erec- 
tion of a rotary converter ? 

Ans. First — It should be protected from moisture. Sec- 
ond — It should be protected from dust or dirt. Third — It 
should be in a well ventilated room and kept as cool as 
possible. 

919. Should the frame of the machine be insulated? 

Ans. Generally speaking the strain on the winding in- 
sulation will be decreased, and danger to attendant increased 
by insulating the frame. 

920. If a rotary has been exposed to dampness how may 
it be dried out ? 

Ans. By running it with about 10 per cent of the nor- 
mal A. C. voltage, while at same time observing certain 



- Questions and Answers 1293 

precautions noted in the text of this book under head of 
rotary converters. 

921. What method should be pursued in caring for the 
commutator ? 

Ans, Wipe it off with a piece of canvas — never use waste. 
Lubricate it with a very small quantity of vaseline^ or oil 
applied with a piece of cloth. See that none of the segments 
is at all loose. 

If it gets out of true turn it down. 

932. If a commutator gets hot while carrying only a 
normal load what should be done ? 

Ans. Heating under such conditions is an indication 
that the commutator is worn out, and should be replaced 
by a new one. 

923. Give some of the causes of sparking at the brushes. 
Ans. Brushes may not have proper lead. 

Brushes may not fit commutator. 
Brushes may be burned on end. 
Commutator surface may be rough. 

924. What is meant by a rotary bucking? 

Ans. When arcing occurs between two adjacent brush 
holder arms, thus short circuiting the machine. 

925. Name a few of the principal causes of bucking. 
Ans. Eough or dirty commutator. 

Excessive voltage. 
Fluctuations in the voltage. 

926. What is an oscillator, and what is its function? 

Ans. An oscillator is a device operated either magnet- 
ically, or by mechanical means, and its function is to pro- 
duce a slight, periodic movement of the armature shaft 
endwise. 

927. Why is this endwise movement of the shaft neces- 
sary? 



1294 Steam Engineering 

Ans. In order to prevent the wearing of grooves in the 
commutator. 

928. Wbat is meant by the hunting of a rotary con- 
verter? 

Ans. It is a slight change of the speed of the armature. 

929. What is the cause of hunting? 

Ans. Irregularities in the speed of the generator deliv- 
ering current to the rotary^ thus causing a slight difference 
in the relative positions of the armature of the two machines, 
resulting in a change in the phase positions of the generator 
^. M. F. and the counter E. M. F. of the converter. 

930. What are the usual methods of starting rotary con- 
l/'erters ? 

Ans. First — By a separate A. C. starting motor. 

Second — By applying direct current to the commutator. 
This starts the converter as a shunt motor. 

Third — By applying alternating current directly to the 
collector rings. This starts the converter as an induction 
motor. 

931. What is meant by synchronizing a rotary converter ? 
Ans. Bringing it to the same frequency, the same phase, 

and the same voltage as the generator from which it is 
receiving current. 

932. What method is employed to determine when the 
machines are in synchronism? 

Ans. There are several methods, the most common one 
being by means of incandescent lamps connected in series 
with the two machines. 

933. What is a synchroscope? 

Ans. It is an instrument for determining when electrical 
machines are in synchronism. 
\ 934. What is an automatic synchronizer? 



Questions and Answers 1295 

Ans. It is a device that will automatically synchronize \ 
two electrical machines; also connect a synchronized ma- 
chine with the main by means of an electrically operated 
switch. 

935. Name two important points to be looked after be- 
fore starting a rotary converter. 

Ans. First — See that both the A. C. and D. C. brushes 
are properly adjusted and that every thing is clear about 
the converter. Second — See that the switches on board are 
open on both the A. C. and D. C. sides^ and that the resist- 
ance of the rheostat is all cut in the field circuit. 



Oil Switches 



As considerable space has been devoted to oil switches, 
the subject will be continued still further by a brief expla- 
nation of the construction and operation of this type of 
switches^ and also of oil circuit breakers. The principle of 
construction is shown in Fig. 603. On the right and left 
hand are two metallic rods which descend through insulating 



e4:::-;: 



i^~} 






it 



Fig. 603 

blocks, and carry springs at their lower end projecting there- 
from. Another metallic rod descends between these two, 
and carries a cross-piece at its lower end, having beveled 
carbon contacts C. C. facing upward. This rod moves up 
and down through an insulating block, and it is connected 
to one lead of the circuit, while both side rods are connected 
! 1297 



1298 Steam Engineering 

to the other. When the central rod is raised the carbon 
blocks C. C. enter between the springs and make the contact, 
closing the circuit. When lowered it opens the circuit. Thus 
far the action of the switch is similar to the ordinary switch, 
but in order to prevent the formation of arcs, and to insure 
definite action in the opening or closing of the circuit, the 
lower portion of the mechanism is immersed in oil con- 
tained in a tank which is shown in section in the diagram 




Fig. 604 • 
type i westinghouse oil switch 

Fig. 603. Oil switches are made in many different styles, , 
but the one feature of the complete submersion of all live 
parts in oil, governs all. They are also as a rule held in the 
open position, either by gravity or by special locking mechan- 
ism consisting of a safety catch that holds the switch open 
until released by pressure of a button in the end of the 
operating handle. 

The development of the oil switch, and circuit-breaker has 
produced what is probably the most valuable addition to 

I 



ai 



ti( 



Oil Switches 1299 

high-potential line apparatus made during the last ten 
years. It is indeed likely that the development of high-ten- 
sion transmission of power would have been very seriously 
hampered but for the invention of the oil switch. 

This use of oil has made it possible to rupture easily and 
safely^, circuits carrying heavy currents at high voltage and, 
further^ to open these circuits under conditions of short 
circuit. The possibility of opening high-tension circuits 
under conditions of heavy overload has made possible the 
development and application of the present system of relays. 




Fig. 605 
type d westinghouse oil switch 

By means of these relays, used in connection with oil circuit- 
cbreakers, perfect protection can be secured for the apparatus 
cto which they are applied. 

The term "switch^^ is given to those pieces of apparatus 
.in which the contacts are similar to the ordinary switch, 
,and are opened and closed by hand. Devices in which the 
contacts tend to separate, and are only held in a closed posi- 
tion by means of triggers and toggles are called "circuit- 
^breakers.^^ 



1300 



Steam Engineering 



The Westinghouse oil switches are essentially knife 
switches immersed in oil^ the blades being connected to a 
common operating lever by specially treated wooden rods. 
The knife-blade contacts are used^ as they give the most 
perfect contact and therefore the lowest temperature rise. 

Fig. 604 shows a Westinghonse type I oil-switch for 
switchboard use only. Fig. 605 shows the type D Westing- 
house oil-switch for outdoor service, the casing being mois- 
ture proof, and the leads brought out underneath through 




Fig. 606 

sealed bushings as shown. Fig. 606 shows the same switch 
with the oil tank removed. Fig. 607 shows the Westing- 
house type B oil circuit-breaker, designed for potentials 
from 3,300 to 22,000 volts, and currents from 300 to 1,200 
amperes. This device is a double-break, oil circuit-breaker. 
It may be automatic or non-automatic, and may be placed 
on the back of the switchboard, or arranged for distant con- 
trol through rods and levers. 

Through a very simple system of levers, the operating 
handle is connected to a cast-iron cross bar, to which are 



Oil Switches 



1301 



fastened the movable contact arms. To the lower end of 
the wooden arm is fastened a metal yoke with a conical 
eontact on either end. When the circuit is closed these 
contacts engage with two stationary contacts^ forming one 




Fig. 607 
i type b westinghouse oil circuit breaker 

pole of the breaker. Each stationary contact is supported 
by a porcelain insulator^ rigidly secured to the frame. The 
leads are brought to the terminals of the stationary contact 
within the insulator, forming an unbroken and continuous 



1302 



Steam Engineering 



insulated conductor between the circuit-breaker^ and the 
bus-bar or line. Each pole of the circuit-breaker has a tank 
in which its live metal parts are immersed in oil^ each tank 
being entirely independent of the adjacent one. 

These tanks have a lining so formed as to reduce the 
quantity of oil required and which serves as a barrier be- 




FiG. 608 

TYPE E WESTINGHOUSE OIL CIRCUIT BREAKER 

tween the two stationary contacts^ yet allowing ample space ^ 
for the movement of the wooden arm and its contacts. The 
lining serves as an insulation^ and reduces to a minimum all 
danger of the arc communicating through the oil. Any one 
of the tanks may be removed without interfering in any 
particular with the others. Fig. 608 shows the type E 



Oil Switches 1303 

Westinghouse oil circuit-breaker^ electrically operated. This 
circuit-breaker is also designed for high potentials, and 
heavy currents. 

A simple system of toggles and levers is mounted on the 
top of the breaker^ and a powerful electro-magnet is arranged 
with its movable core attached to the lever system, so that 
when it is drawn into the coil, the circuit-breaker will be 
closed. A small single-pole, double-throw switch is mount- 
ed on the breaker, and is operated by the motion of the 
levers in opening or closing the circuit; it controls the 
tell-tale indicator, and lamp which are mounted in view of 
the operator. These circuit-breakers are operated by 125 
volts direct-current, and are calibrated for 3,000 alterna- 
tions. 

ELECTRO-METERS. 

Galvanometers. — An electric current passing near a mag- 
netic needle deflects the needle, and if the current is passed 
first over the needle and then back under it in an opposite 
direction, the needle will be still further deflected. 

An instrument consisting of a coil of wire carrying the 
current to be tested, and a magnet ; the two being so ar- 
ranged that one can be deflected, is called a galvanometer. 

There are two types, the Thompson and the D^Arsonval. 

The Thompson type has the coil of wire stationary, and 
the light magnetic needle suspended by a silk thread. These 
can be made more sensitive than the other type, but are not 
portable, and external fields have a great influence on them, 
causing them to give false indications. This is prevented 
by thick soft iron cases, much too heavy to be carried 
around. 

The silk suspension makes the needle sensitive to vibra- 
' tion. 



1304 Steam Engineering 

It is a fine laboratory instrument^ and with modified con- 
struction has been used in the workshop and field, but for 
this work the D'Arsonval is much better. 

The D^Arsonval type has a very small, light coil of wire 
suspended by a fine bronze wire between the poles of a sta- 
tionary magnet. Since the movable part is iiot a magnet 
except during the actual instant of the test, outside mag- 
netic fields have no influence on its motion. To shield it 
during test, a thin soft iron or steel case is put on the in- 
strument which does not affect its portability. These covers 
are usually copper, brass or nickel plated for appearance 
sake, but the actual material is iron for the purpose of 
shielding the instrument. 

These D^Arsonval galvanometers are not so sensitive as 
the other type, which for ordinary work is a great advan- 
tage. 

Both of these types have the needle swinging over a 
circular scale divided into degrees, or may have a small 
mirror attached so that the deflection may be read by the 
motion of a spot of light moving along a long ruler sup- 
ported about a yard away from galvanometer. 

As mentioned before, twice the current does not give 
twice the deflection, but by sending known currents through 
a galvanometer, and marking a scale with pen and ink we 
could make an ampere meter. This is called Calibration. 

Ammeters and Voltmeters. — The ammeters and volt- 
meters of commercial work are all special adaptations of 
the D'Arsonval galvanometer or, for the least accurate work 
such as on switchboards ; they are of the magnetic vane type. 

The Weston instruments are D^Arsonval galvanometers. 

Fig. 609 shows an instrument with the cover removed. 
A large permanent magnet of U shape is supported by a 
gun-metal casting screwed .to the ends of the limbs, and 



Electro Meters 



1305 




Fig. 609 
interior of weston instrument 



1306 Steam Engineering 

the whole of the working part is. built up on this mag- 
net independent of the ease, so that the movement can 
be removed bodily from the case by simply taking out 
one screw which holds the gun-metal casting in place. 
The inside polar faces of the magnet are surfaced up so 
as to come closely into contact with wrought-iron pole 
pieces which are bored out to about 1 in. diameter, and 
fixed rigidly in their place with screws passing through 
the limbs of the magnet. To these pole pieces a second 
gun-metal casting is screwed, which forms a support for a 
soft iron cylinder % in. diameter inside the bored out pole 
pieces, and also a support for the scale. The soft iron 
cylinder fills up most of the space between the pole pieces, 
allowing an air space at either side of % ^"^-^ and in this 
space a fairly strong, uniform, magnetic field exists. A coil 
of fine insulated copper wire of about twelve turns is 
wound on a thin brass frame, large enough to embrace the 
soft iron cylinder, with freedom to move in the space be- 
tween it. and the pole pieces. This is pivoted in jeweled 
bearings which are screwed to the pole pieces, but insulated 
from them, forming little bridges across, and the ends of 
the coil are connected to these bridge pieces by spiral springs, 
one at the top and the other at the bottom of the coil, the 
springs being wound in opposite directions, so that when 
one is wound up by a movement of the coil the other is 
unwound. This arrangement corrects for any variation in 
temperature, for the effect on one spring would be counter- 
acted by the opposite effect on the other. The coil normally 
lies at 45° to the line joining the poles of the magnet, and 
consequently the magnetic field created by a current in the 
coil will be displaced relatively to the field of the horseshoe 
magnet as shown in Fig. 610, and the lines twist the coil 
through a certain angle against the action of the spiral 



Electro Meters 



1307 




Fig. 610 

diagram of magnets, flux, coil and inner core of weston 

instrument 




Fig. 611 
view of movement of weston instruments 



1308 Steam Engineering 

springs^ the angular movement of the coil depending on 
the strength of the current in the coil and the strength of 
the field in which it is placed. 

To the coil is attached a pointer of aluminum, the whole 
being balanced so that the instrument can be read in any 
position, and the pointer and scale are bent up so as to come 
near the front of the case. 

A perspective view of the movement is shown in Fig. 611. 

In this instrument the whole current does not go through 
the coil, but only a small fraction of it. The main part of 
the current crosses from one terminal to the other by a 
broad strip of metal under the base of the instrument, 
while the coil is placed as a shunt across the terminals, or 
as a conductor in parallel wUh the metal strip (Fig. 612), 
and consequently the ratio of the currents in the strip and 
in the coil will be inversely proportioned to their resistances. 
Now with a given strength magnetic field due to the magnet 
and a given elasticity of the spiral springs, it will require 
a certain number of ampere turns in the coil to produce 
the full deflection on the scale. This can be secured by 
adjusting the resistance of the strip connecting the term- 
inals so that the same movement will do for any instrument. 
Thus, suppose the instrument were required to read to 
a maximum of 10 amperes, and we required 1 ampere in 
the coil to give the maximum deflection, then the resist- 
ance of the coil must be 9 times that of the strip, so that l 
the current will divide at the terminals, 9/10 going through 
the metal strip and 1/10 through the coil. If the instru- 
ment is required to read to a maximum of 100 amperes, 
then the metal strip must have 99 times less resistance 
than the coil, and the current will then divide at the term- 
inals, 99/100 going through the strip and 1/100 going 
through the coil, which will give a reading to the full range 



Electro Meters 



1309 



of the scale as before. By the arrangement of the pole 
tpieceS;, and wrought iron cylinder the field due to the per- 
manent magnet is practically uniform over the range of 
3 movement of the coil, and so the scale readings are the 
^same size throughout. Should the permanent magnet 



^ 



\ 




Fig. 612 
magnet and shunt of weston ammeter 



/ary in strength, the instrument would not read correctly, 
f;)ut the magnets are so treated that the falling off in strength 
)ver a number of years is inappreciable. 
I The strip or shunt for portable instruments is always 
^nside the case, while for switchboard instruments the shunt 



1310 



Steam Engineering 



is too large (Fig. 613) and is placed separately on the back 
of the board. Leads are rim along the board to the meter 
terminals which project through holes in the board from 
the meter which is in front. 




Fig. 613 
external shunts for ammeters. 1000 and 5000 ampere sizes 

Such a switchboard instrument is shown in Fig. 614 and 
Fig. 615. 

A Voltmeter is made by removing the metal strip or shunt 
connecting the terminals .and placing a resistance coil in 
series with the moving coil. 



Electro Meters 



1311 



As it takes 1/100 amperes to swing the pointer over full 
scale for every volt the instrnment reads^, it must have 100 
ohm's in the resistance coil. 

A 500 volt instrnment will have 500^000 ohms resistance^ 
and hence 1/100 amperes will flow through the moving coil. 

The moving coil is wound on a copper^ or aluminum 
frame, which when it swings has current induced in it by 
the magnets and stops vibrating very quickly; in fact, you 
cannot detect any vibration. The needle seems to move to 




Fig. 614 
switch board instrument 

a certain spot and stop dead. This is called a ^^dead beat'^ 
needle. 

Some instruments have electro-magnets instead of per- 
manent magnets. The Thomson Astatic instruments are 
of this type. Two of these instruments are shown in Figs. 
615 and 616. This latter has a scale or dial of opal glass 
with an electric light behnd it. This makes the instrument 
easily read from a distance or at night. These are called 
^^illuminated dial instruments.^^ 



1312 



Steam Engineering 




Fig. 615 
switch boakd ammeter 




Fig. 616 
illuminated dial instrument 

The instrument shown in Fig. 614 has an extra hand 
ending in a ring. This can be set at the voltage it is 
desired to maintain. The most hasty glance will then show 
whether the voltage is too high or too low. 



Electro Meters 



1313 



In order to save space on switchboards some instruments 
are made thin and broad and are set horizontally or ver- 
tically. 

Fig. 617 shows the exterior and interior of a Thomson 
Edgewise Ammeter. 

The Thomson Inclined Coil instruments as shown in 




Fig. 617 
thomson horizontal ammeter 

Fig. 618 are portable instruments used for alternating cur- 
rent only. In an emergency they can be used to measure 
direct current by readings then reversing current, reading 
again^ and averaging results. 

The action of the masrnetism of the inclined coil is to 



line position. 



1314 



Steam Engineering 



The Weston instruments described are for direct current 
only. The company makes an alternating current volt- 
meter but no ammeter. Thomson Astatic instruments are 
for direct current. The Thomson Inclined Coil in portable, 
or edgewise switchboard form is for alternating current. 

Wattmeters. — By combining two coils, one movable, the 
other stationary, one attached as a voltmeter with series 
resistance, the other attached as an ammeter, with a shunt, 
we get an instrument whose needle indicates power or watts. 
These are called indicating wattmeters. 



i^ij) 




Fig. 618 
thomson inclined coil instrument 

The recording wattmeter records watt-hours. A w^tt- 
hour is one watt of power used for an hour, or any combina- 
tion like one-quarter of a watt for four hours, etc. 

The Thomson Eecording Watt-Hour Meter is used for 
direct, or alternating current. It is shown with dust-proof 
case removed in Fig. 619. The connections made to it are 
shown in Fig. 620. By "lights'' in the figure must be 
understood any load at all. 

The meter consists of an electric motor whose armature 
A, Fig. 620, is supplied with current from the mains 
through a high resistance P in the back of the instrument, 
and a small field coil on right-hand side. 



Electro Meters 



1315 



This armature is in shunt across the circuity hence its 
current is proportional to the voltage. 

The main current passes through the field P^ hence the 
strength of the field is proportional to the current. 

The speed of the motor is therefore proportional to both 
current and voltage^ that is to the power^ or watts. 




Fig. 619 
thomson recording watt-hour meter 

The armature shaft goes on past the commutator, to a 
cyclometer with dials like a gas meter. The revolutions are 
here recorded as watt-hours. 

The auxiliary field is just strong enough to nearly over- 
come the friction in the bearings and cyclometer, so that the 
smallest current through the mains will produce rotation. 

At the bottom of the armature shaft is an aluminum 
disc revolving between the poles of permanent magnets. 



1316 



Steam Engineering 



This device prevents the meter from running at too great a 
speed and gives an adjustment for accuracy. 

The further out the magnets are swung the faster is the 
motion of the metal passing between their poles^ and the 
greater a retarding effect they produce. 




Fig. 620 
diagram of connections. thomson recording watt-hour meter 

A meter running too slow from agC;, or. dirty bearings 
could be brought up to proper speed by swinging the mag- 
nets in a little. 

For heavy currents the appearance of the meter is quite 
different, as is shown in Fig. 621. The retarding device is 



Electro Meters 



1317 



enclosed in a case, and the whole instrument is enclosed 
in a dust-proof glass case. 

Switchboard Maintenance. — The increasing relative cost 
of switchboard apparatus' in power plants justifies more 
thorough inspection on the part of attendants than at 
present obtains in many installations. There is a feeling 




Fig. 621 
large capacity thomson recording watt-hour meter 



in some quarters that if a switchboard is blown out every 
day with compressed air, and the instruments wiped with a 
dust cloth, nothing further in the way of inspection need 
be done until something goes wrong. 

There are more moving parts on a modern switchboard 
than one would at first suppose, and a certain amount of 



1318 Steam Engineering 

attention is an essential of continuous reliable service. In 
addition to the indicating and recording instruments there 
are time limit relays, circuit-breaker controls, oil switch 
mechanisms and other contacts to look after, while the 
possibility of overheated parts of switches and coils is always 
present. Oil switches in operation should be inspected for 
overheating at least three times a day during the heaviest 
part of the load, and the binding posts of potential trans- 
formers, regulators and instruments should be looked after 
every two or three weeks with an eye to their becoming loose. 

The oil tanks on oil switches ought to be dropped cer- 
tainly once in three months, and the contacts carefully ex- 
amined to locate any broken or bent springs, burned con- 
tacts or loose connections. When these contacts are cleaned 
with a file or in any way where there is a chance of per- 
sonal connection with the wiring system, the utmost care is 
essential that current should be cut off, and high-potential 
contacts avoided. Knife switches for simple disconnect- 
ing work are worth many times their cost. 

The solenoid equipment of time-limit relays are often 
neglected for long periods. The adjustment of these de- 
vices should be tested every two or three months and the 
contacts cleaned with the finest sandpaper or emery cloth. 
There is a tendency sometimes to forget that these relays 
are delicate apparatus. The adjustment of spring tension 
to hold contact pieces in place and the varnishing of 
solenoid plungers need to be carefully done. No little 
trouble can arise by careless varnishing of plungers so 
that they stick in one position and do not respond to the 
load variations above normal. Another point likely to be 
neglected is the care of the leather diaphragm on the relay 
bellows. This should be dressed with neatsfoot oil every 
two or three months to prevent it from becoming stiff and 



Electro Meters 1319 

hard. Lightning arresters should always be examined and 
placed in condition after a storm; rheostat contact points, 
fixed and movable, carbon brakes and copper feeder and 
switch jaws all need regular inspection just as much as 
commutators, brushes and bearings. 

LIGHTNING AERESTERS. 

Ordinarily a lightning discharge, which is an equaliza- 
tion of potential between the earth, and either clouds or 
saturated atmosphere above the earth, will take place 
through the path of least resistance, but, as pointed out by 
Eowland, there is a certain factor' somewhat resembling 
inertia which causes the lightning, once started, to follow 
sometimes an irregular path, similarly, for instance, as 
when a piece of paper is suddenly torn. Transmission lines 
and buildings of ordinary height surrounded by trees are 
not peculiarly subject to damage from lightning, because 
they cover a comparatively small portion of the earth, and 
are surrounded by objects of greater height, which offer a 
better path for the lightning discharge to the earth. They 
do, however, receive some discharge, and the damage which 
might be done can be very great. It is therefore, necessary 
to provide ample protection. 

Generally speaking, the severe manifestations of light- 
ning are confined to a relatively small area, which rarely 
Exceeds in extent an area of about one square mile. It may 
be concluded from this that protective apparatus situated at 
certain points along the line will afford no protection to 
remote points. 

G-enerally speaking, the broad requirements for light- 
ning protection consist in supplying paths to ground for any 
charge which might accumulate on lines, or machinery from 



1320 Steam Engineering 

any cause whatever. The ideal arrester will cause excessive 
potential differences to be relieved instantaneously, and stop 
the flow of current, as soon as the potential has fallen to 
safe limits for the line. No one type of lightning arrester 
fulfills all requirements, and accordingly it is found expe- 
dient to use different types and combinations, in different 
situations, and under different conditions. 

For the protection of electric circuits, grounded guard 
wires are best, and when the cost over the whole system 
would prove prohibitive, they should be confined to such 
localities as are peculiarly liable to suffer destructive dis- 
charges. Three ground wires are required for the best 
practicable protection. One of these should be placed on 
top, and in the middle of the line, and should be a heavy 
galvanized steel cable, and the other two, which should be 
heavy telegraph wires, are placed outside, and above the 
top side conductors. The ground wires should be earthed 
at every pole for the first 10 or 12 poles from the building, 
and at every second pole on the rest of the line. Graded 
resistance, or aluminum type lightning arresters should be 
installed on every feeder issuing from the station, and on 
the primary and- secondary of every transformer, and a 
surge protector in the station, but choke coils having a 
large number of turns should not be used in the station, 
as they represent a possible source of danger. 

Where from internal causes, such as flashing over a 
bushing or insulator, the arcing ground sends a series of 
oscillations through the circuit, it is necessary to provide an 
arrester which will continue to discharge the abnormal volt- 
age for a sufficient period to permit the operator to locate 
and isolate the trouble. Half an hour is generally found 
to suffice for the period of an arrester, as this will give time 



Lightning Arresters 1321 

to discover the point of trouble, where this is remote from 
the station. 

Horn arresters placed along the line at various places 
will do much to protect insulators from puncturing or arc- 
ing across. These horn arresters should be adjusted to arc 
at something below the wet arc-over voltage of the insu- 
lators, and should be connected to earth direct. Only one 
phase per pole should be protected by a horn arrester, so 
that in the event of two horns arcing simultaneously, 'the 
earth resistance can be utilized to limit the discharge. 
Ground wires should not be grounded at poles carrying horn 
arresters. 

Lightning rods above wooden poles are an advantage. 
Graded resistance multigap, or aluminum arresters should 
be used on outgoing and incoming lines. Choke coils 
should be in the circuit just back of the arresters, which, in 
turn, are placed quite near the passages and are provided 
with disconnecting switches. 

Multigap Arresters.— The general theory of the multigap 
arrester is as follows: When voltage is applied across a 
series of multigap cylinders, the voltage distribution is not 
uniform. The voltage distributes according to the capacity 
of the cylinders, both between themselves and also to ground, 
and the capacity of the cylinders to ground, results in the 
concentration of voltage across the gaps nearest the line. 
Fig. 632 shows the theoretical voltage gradient along an 
arrester. The voltage across the end gaps reaches a certain 
value. They arc across, passing the strain back to the other 
gaps, which in turn are over until the spark has passed en- 
tirely across. The arrester in this manner arcs over at 
voltage much lower than would be required if the voltage 
distributed evenly. When the arrester has arced over, an^ 
current is flowing the voltage then does distribute evenly 



1322 



Steam Engineering 



between the gaps, and is for this reason too low to maintain 
an alternating current arc. The arc, therefore, lasts only 
to the end of a half cycle, and then goes out. The maxi- 
imum voltage per gap at which the arc will extinguish at 
the end of the half cycle depends to a great extent upon the 
metal of the cylinders. Thus some metals are more efficient 
than others in extinguishing the arc. 



k y ^ 



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When the voltage of an alternating current passes through 
zero, of course no current flows. Before the current flows 
in the reverse direction the voltage must again break 
through the dielectric. The voltage required to do this 
depends upon how much the dielectric has been 
weakened by the passage of the arc. The cooler the arc, 
the less the dielectric is weakened, and the higher will 
be the voltage required to reverse the arc. As the temper- 
ature of the arc depends. upon the boiling point of the 
cathode metal, in very much the same way as the temper- 



Lightning Arresters 



1323 



ature of steam depends upon the boiling point of the water, 
metals with low boiling points are used for the lightning 
arrester cylinders, in order to keep down the arc tern* 
perature. 

The use of resistance in a lightning arrester needs very 
careful consideration. Lightning does not readily pass 



LlM^ 




Fig. 623 
station arrester 

through resistance, especially when in series with multigaps, 
and therefore series resistance should not be used. At the 
same time it is very desirable in some way to limit the cur- 
rent. This problem has at last been solved by use of a low 
shunt resistance, shunting a part of the gaps and so propor- 
tioned to divert the current from the gaps, after the dis- 
charge has passed the ground. Shunt resistance has been 



1324 Steam Engineering 

used before, but never for this purpose, and was never made 
low enough to divert the arc in this way. 

It is obvious, of course, that a discharge taking place 
through a high resistance will not relieve the line except in a 
case of the static. What happens, however, is something 
like this: When a surge of dangerous voltage rises, and 
before it reaches a danger point, the series gaps arc over. 
The series gaps then being practically short-circuited by the 
arc the voltage concentrates across the lowest division of the 
shunted gaps, and these at once also break down. The cur- 
rent is then limited by the medium resistance, and the volt- 
age is concentrated across the second division of the arrester. 
If these gaps break down, the discharge is limited only by 
the low resistance, which should take care of most cases. 
If necessary, however, the voltage can "break back^^ in this 
way, and cut out all resistance. The number of gaps to 
rectify depends largely on the current that flows. In this 
arrester the number of gaps discharging increases as the 
limiting resistance decreases. The arrester will, therefore, 
operate and extingush the arc at the end of the half-cycle 
no matter which path the current takes. 

Instructions for Installing 600 Volt D. C. Aluminum 
Lightning Arresters. — The principal elements of this ar- 
rester are two cells, each consisting of two concentric alum- 
inum plates immersed in an electrolyte contained in a 
glass jar. 

The outside plate of each cell should be the positive, and 
the inner one the negative, as indicated by the marking of 
the four studs on the porcelain cover, two studs supporting 
each plate. 

In addition, station arresters are fitted with a balancing 
resistance in shunt with each cell and a series fuse; car 
arresters, with a series fuse as connecting link between the 



Lightning Arresters 



1325 



two cells. A diagram of connections is shown in Fig. 624. 

To Fill the Arrester. — Unscrew the metal rings at the 
top of the jars and lift off the porcelain covers^ with the 
aluminum plates attached, without removing the connec- 
tion between the two units. Pour enough electrolyte into 
the jars to bring the level to about one inch from cover. 
Add % pint of oil to each jar. 

In transferring the electrolyte, or oil from the carboy, 
or other container used for shipping,* employ nothing but 



i//Vf 




Fig. 624 
car arrester 

clean aluminum, or glass vessels and funnels. Take every 
precaution to prevent any dust or other material from get- 
ting into the electrolyte. 

Before connecting permanently to the circuit it is ad- 
visable to connect the arrester in series with five 120 volt 
incandescent lamps across the 600 volt circuit. The lamps 
will burn brightly for an instant and then rapidly diminish 
I to darkness, thus indicating that the film is all right. If the 
llamps are dark at first, the circuit should be opened and 



1326 Steam Engineering 

closed^ and a small snappy spark at the contact point will 
show that the circuit is complete and the film in proper 
condition. The lamps should then be removed and the cells 
connected directly to the circuit. 

Connections, — These should be as short as possible be- 
tween line and ground^, and only to those points on which 
the terminals are placed when shipped. Use only the style 
of terminal furnished^, as they afford no chance for a short 
circuit by swinging against the opposite terminal. In the 
case of pole arresters the test with series lamps^ as de- 
scribed abovC;, should be made before making the last con- 
nection^ otherwise there may be a considerable flash due to 
an instantaneous current rush. The ground connection of 
these line arresters should be made directly to the ground 
bus, and driven pipe ground. 

Operation. — If the arrester has stood assembled in its 
electrolyte for a month or more, when reconnected there will 
be a momentary rush of current which may amount to sev- 
eral hundred amperes. To avoid this current rush/ use 
lamps in series as explained above. 

It is preferable, however, when an arrester is to be left 
out of service for some time, to pour out the electrolyte and 
oil, wash the plates and jars with clean water and put the 
plates back in the jar. When replacing in service, make the 
usual test with lamps. 

After operating for some time, arresters without balanc- 
ing resistance, may divide the voltage unequally between 
cells, which is indicated by sparkling of the plates in one 
cell. In such cases the arrester should be removed from the 
circuit, and connected to a test circuit with a bank of five 
lamps in shunt with each jar; that is ten lamps from line to 
line with the middle point connected between cells. After 
operating this way for several hours remove the lamps. If 



Lightning Arresters 1327 

sparkling has ceased^ the arrester is ready to be placed in 
service. 

After the arrester has been in operation for a short time, 
the electrolyte may become dark in appearance, but this 
condition is normal. 

Inspection should cover answers to the following ques- 
tions: 

1. Are there any loose connections? 

2. Is the level of the electrolyte at the proper height? 

3. Are the positive plates worn off at the surface of 
the electrolyte? 

4. Are the connecting leads as short as possible ? 

5. Does either cell sparkle? 

Multigap Lightning Arresters for Alternating Currents. 
— These arresters, designed upon an elaboration of Prof. 
Elihu Thomson^s fundamental patents, consist of a series 
of spark gaps shunted by graded resistances, but without 
series resistance. The advantages possessed by them are: 

1. Uniform voltage discharge over a wide range of 
frequency due to graded resistance. 

2. Shunting the dynamic current through resistance. 

3. The "breaking back^^ action on low frequency surges. 

4. Fuse in ground leg of non-grounded neutral systems. 

5. Adjustable gap in each leg shunted by a fuse. 

6. Metallic resistance rods of improved composition. 

7. Durable knurled cylinders of special alloy. 

8. General Electric standard multiplex connection. 
When properly installed they will perform the following 

functions : 

First. Prevent excessive rise of potential of a transi- 
tory nature between lines, as well as between lines and 
s^round. 



1328 Steam Engineering 

Second, Eestrain the flow of electric current across 
the gaps, and extinguish the arc when normal potential is 
restored. 

Third, Discharge high potentials covering a wide range 
of frequency. 

The essential elements of the arrester are, a number of 
cylinders spaced with a small air gap between them and, 
placed between line and ground, and between line and line. 
In operation the multigap arrester discharges at a much 
lower voltage than would a single gap having a length 
equal to the sum of the small gaps. 

In explaining the action of multigaps, there are three 
things to consider: 

1. The transmission of the static stress along the line 
of cylinders. 

2. The sparking of the gaps. 

3. The action and duration of the dynamic current 
which follows the spark, and the extinguishment of the 
arc. 

A spark may be defined as conduction of electricty by 
the air, and an arc as conduction of electricity by vapor of 
the electrode. 

Distribution of Static Stress Along Cylinders, — The cyl- 
inders of the multigap arrester act like plates of condensers 
in series. This condenser function is the essential feature 
of its operation. When a static stress is applied to a series 
of cylinders between line and ground (Fig. 625), the stress 
is instantly carried from end to end. If the top cylinder 
is positive it will attract a negative charge on the face of the 
adjacent cylinder, and repel an equal positive charge to the 
opposite face, and so on down the entire row. The second 
cylinder has a definite capacity relative to the third cylinder 
and also to the ground ; consequently the charge induced on 



Tjightning Arresters 



1329 



the third cylinder will be less than on the second cylinder, 
due to the fact that only part of the positive charge on the 
second cylinder induces negative electricity on the third, 
while the rest of the charge induces negative electricity to 
the ground. Each successive cylinder, counting from the 
top of the arrester, will have a slightly smaller charge of 




\J/Fes/stance 



o 
o 



? 



Fig. 625 
arrangement of resistances 

electricity than the preceding one. This condition has been 
expressed as a ^^steeper potential gradient near the line.^^ 

Sparking of the Gaps, — The quantity of electricity in- 
duced on the second cylinder is greater than on any lower 
cylinder, and its gap has a greater potential strain across it 
as shown by Pig. 626. When the potential across the first 



1330 



Steam Engineering 



gap is sufficient to sparky the second cylinder is charged to 
line potential, and the second gap receives the static strain 
and breaks down. The successive action is similar to over- 
turning a row of nine-pins by pushing the first pin against 
the second. This phenomenon explains why a given length 
of air gap concentrated in one gap requires more potential 
to spark across it, than the same total length made up of a 
row of multigaps. As the spark crosses each successive 
u V ^ 



-^j^iQii9if9iy9(i9<i9ii9<jQii9ii9ii9iigji9<i9iiQii9i(9<i9ii9(iQii2iiQiiQ<igiiQiig^ 
TTTTTT TTTTTTTTTTTTTTTTTTTTTTT TTTTTT 




Gaps 9 

Fig. 626 

diagram showing condenser action of cylinders and 

potential gradient for static stress 



gap, the potential gradient along the remainder readjusts 
itself. 

Row the Dynamic Arc is Extinguished. — When the 
sparks extend across all the gaps the dynamic current will 
follow if, at that instant, the dynamic potential is sufficient. 
On account of the relatively greater current of the dynamic 
flow, the distribution of potential along the gaps becomes 
equal, and has the value necessary to maintain the dynamic 



Lightning Arresters 



1331 



current arc on a gap. The dynamic current continues to 
flow until the potential of the generator passes through 
zero to the next half cycle, when the arc-extinguishing 
quality of the metal cylinders comes into action. The alloy 
contains a metal of low boiling point which prevents the 
reversal of the dynamic current. It is a rectifying effect, 
and before the potential again reverses, the arc vapor in the 
gaps has cooled to a non-conducting state. 



^^^ 




Fig. 627 

CONNECTIONS FOR 33,000-VOLT Y SYSTEM WITH GROUNDED NEUTRAL 

The Cumulative or Breaking Bach Effect. — The graded 
shunt resistances (Figs. 627 and 628) give a valuable effect 
not brought out in the previous description, where the 
larrester is considered as four separate arresters. This is the 
icumulative or breaking back action. 

When a lightning strain between line and ground takes 
place, the potential is carried down the high resistance, H, 
to the series gaps, GS, and the series gaps spark over. Al- 



1332 



Steam Engineering 



though it may require several thousand volts to spark across 
an air gap^, it requires relatively only a few volts to main- 
tain the arc which follows the spark. In consequence, when 
the gaps GS spark over, the lower end of the high resistance 




Fig. 628 
connections for 33,000-volt delta or ungrounded y systems 

is reduced practically to ground potential. If the high 
resistance can carry the discharge current without giving 
an ohmic drop sufficient to break down the shunted gaps 
GH, nothing further occurs — ^the arc goes out. If, on the 



Lightning Arresters 1333 

contrary^ the lightning stroke is too heavy for this, the 
potential strain is thrown across the shunted gaps, GH, 
equal in number to the previous set. In other words, the 
same voltage breaks down both of the groups of gaps, GS 
and GH, in succession. The lightning discharge current is 
now limited only by the medium resistance, M, and the 
potential is concentrated across the gaps, GM. If the 
medium resistance cannot discharge the lightning, the gaps 
GM spark, and the discharge is limited only by the low 
resistance. The low resistance should take care of most 




Fig. €29 

"V" UNIT OF MULTIGAP LIGHTNING ARRESTERS 

cases, but with extraordinarily heavy strokes and high fre- 
quencies, the discharge can break back far enough to cut 
out all resistance. In the last step the resistance is rela- 
tively low in proportion to the number of shunt gaps, GL, 
and is designed to cut out the dynamic current instantly 
from the gap, GL. The illustration (Fig. 631) of the 2,200 
volt arrester shows that the low resistance actually performs 
this function. This breaking back effect is valuable in 
discharging lightning of low frequency, in a manner better 
than has been obtained before. 



1334 



Steam Engineering 



After the spark passes^ the dynamic arcs are extinguished 
in the reversed order. The low resistance^ Jj, is propor- 
tioned so as to draw the dj^namic arcs instantly from the 
gaps^ GL. The dynamic current continues in the next 




Fig. 630 
installation of a 12,000-volt, three-phase, multigap light- 
ning arrester in the garfield park sub-station of the 
west chicago park commission 



group of gaps^ GM^ until the end of the half cycle of the 
generator wave. At this instant the medium resistance^ M^ 
aids the rectifying quality of the gaps, GM, by shunting 



Lightning Arresters 1335 

out the low frequency dynamic current of the generator. 
On account of this shunting effect the current dies out 
sooner in the gaps^ GM^ than it otherwise would. In the 
same manner^ but to a less degree, the high resistance^ H^ 
draws the dynamic current from the gaps^, GH. This cur- 
rent now being limited -by the high resistance^, the arc is 
easily extinguished at the end of the first one-half cycle of 
the generator wave. 

''V Unit for MuUigap Arresters. — The High-voltage 
Multigap Arrester is made up of "Y^^ units (see Fig. 629), 
each unit consisting of gaps between knurled cylinders^ 
and connected together at their ends by short metal strips. 
The base is of porcelain^ which thoroughly insulates each 
cylinder^ and insures the proper functioning of the multi- 
gaps. 

Cylinders. — The cylinders are made of an improved alloy 
that contains metal of low boiling point which gives the 
rectifying effect^ and metals of high boiling point which 
cannot vaporize in the presence of the one of low boiling 
point. The cylinders are heavily knurled. As the arc plays 
on the point of a knurl it gradually burns back and when 
the metal of low boiling temperature is used up^ the gap 
is increased at that particular point. The knurling there- 
fore^ insures longer life to the cylinder^ by forcing succes- 
sive arcs to shift to a new point. When worn along the 
entire face^ the cylinder should be slightly turned. 

Resistance Rods. — The low resistance section of the 
graded shunt is composed of rods of a new metallic alloy. 
These rods have large current-carrying capacity, and prac- 
tically zero temperature coefficient up to red heat. 

The medium and high resistance rods are of the same 
standard composition previously used. The contacts are 



1336 Steam Engineering 

metal caps- shrunk on the ends; the resistances are perma- 
nent in value and the inductance is reduced to a minimum. 
The rods are designed with a large factor of safety^ and 
have sufficient heat absorbing capacity to take the dynamic 
energy following transitory lightning discharges. They are 
glazed to prevent absorption of moisture^ and surface arcing. 



Lightning Arresters 1337 

Difference between arrester for grounded y and non- 
grounded NEUTRAL SYSTEMS. 

The connection for a three-phase arrester, 33,000 volts 
between lines, are shown in the illustrations (Figs. 627 and 
628). One illustration (Pig. 627) shows the design for a 
thoroughly grounded Y system and the other foi" a non- 
grounded neutral system. The latter (Fig. 628) includes 
delta, ungrounded Y, and Y systems grounded through a 
high resistance. 

The difference in design lies in the use of a fourth 
arrester leg between the multiplex connection and ground, 
on ungrounded systems. The reason for introducing the 
fourth leg is evident. The arrester is designed to have two 
legs between line and line. If one line became accidentally 
grounded, the full line potential would be thrown across 
one leg, if the fourth or ground leg were not present. On 
a Y system with a grounded neutral, the accidentally 
grounded phase causes a short circuit of the phase, and the 
arrester is relieved of the strain by the tripping of the cir- 
cuit breaker. Briefly stated, the fourth or ground leg of the 
arrester is used when, for any reason, the system could 
be operated, even for a short time, with one phase grounded. 

Multiplex Connection. — The multiplex connection con- 
sists of a common connection between the phase legs of the 
arrester above the earth connection, and provides an arrester 
better adapted to relieve high potential surges between lines 
than would otherwise be possible. Its use also economizes 
, greatly in space and material for delta and partially ground- 
I ed or non-grounded Y systems. 

Fuse Auxiliaries. — The practice of introducing an auxil- 
iary adjustable gap between each line wire and its corres- 
i ponding leg of the arrester has been discarded in the new 



1338 Steam Engineering 

design, with marked increase in the sensitiveness of the ar- 
rester. As the gap is necessary, under certain abnormal 
conditions, it is left on the arrester, but short circuited by 
a fuse so that it comes into service only when the fuse blows 
on account of an arc between phase and ground, or some 
similar extremely severe continued strain. The sensitive- 
ness is also greatly increased by the addition of a similar 
shunting fuse around the adjustable gap in the ground leg 
of the arrester. The ground leg is necessary only when 
there is an accidental ground of a phase and, ordinarily the 
increased sensitiveness is maintained continually. 

Location. — Ample wall space should be provided and 
plenty of room in front should be left for the operator. The 
arresters should be placed as near as possible to where the 
lines enter the buildng. The following minimum separa- 
tion distances have proved entirely satisfactory. 

TABLE GIVING PROPER SPACE BETWEEN LIGHTNING ARREST- 
ERS AND SETTING OF ADJUSTABLE GAP. 



Max. 

Volts 


Distance in 

Inches Between 

Live Parts of 

Adjacent 

Phases 


Minimum 
Distance 
B-jtween 
Centers 
(See Note) 


Inches of 
Gap 


7,600 


8" 


28" 


Vi 


12,250 


8" 


28" 


% 


13,500 


8" 


33" 


% 


17,000 


10" 


35" 


% 


22,000 


12" 


37" 


V2 


27,000 


18" 


48" 


1/2 


32,000 


22" 


52" 


% 


37,000 


26" 


56" 


% 



ISToTE — If barriers are used the width of barriers should 
be added to distances given. 



Lightning Arresters 1339 

It is advisable to locate arresters in a dry place^ and 
before assembling them the wooden supports, insulators^ 
etc.^ should be thoroughly dried of all moisture which may 
have collected during transportation. 

The adjustable spark gap on these arresters is shunted 
by a fuse. This fuse blows under certain conditions and 
cuts in the added protection of the gap. The settings of 
this gap for the various arresters should be as already ex- 
plained. 

Voltage Range of Arresters. — Lightning arresters of the 
form described have been designed for voltages from 5,700 
to 37,000. For lower voltages, down to 300 volts, alter- 
nating current, the arresters are of slightly different design, 
havng only two resistance rods. For 300 volts and less no 
resistance is necessary, as the voltage is so low that the arc 
cannot hold. These arresters, therefore, consist simply of 
spark gaps. 

LOW VOLTAGE ARRESTERS — ^FORMS eI AND e2. 

300 TO 5,700 VOLTS. 

The 2,200-volt (Figs. 631 and 634) arrester consists of 
one unit having fourteen cylinders, nine of which are 
shunted by a low resistance and eleven by a high resistance. 
As in the case of the high voltage arresters, the grading of 
resistance provides selective paths for discharges. Its action 
and advantages are therefore similar to those of the high- 
voltage arrester. Accumulated static charges pass off across 
the high resistance, and two gaps. High frequency dis- 
charges pass across all the gaps; discharges of moderate 
frequency across the low resistance, and four gaps. The 
low resistance is so proportioned to the number of shunted 
gaps that the high frequency discharge across these gaps 
is not followed by the dynamic current; the dynamic shunt- 



i 



1340 Steam Engineering 

ing at once to the low resistance. The discharge takes place 
over all the gaps^ but the arcs between the gaps shunted 
by the low resistances are very small compared with the 
bright arcs between the last four gaps. The static dis- 
charge passes through all the gaps, while the half wave of 
dynamic current following the static is shunted part of the 
way by the resistance. 

LINE 




GROUND 

Fig. 631 
form fl, 2,200-volt multigap arrester for stations 

An oscillogram of this phenomenon is shown in Pig. 632. 
The only current in the shunted gaps is the current of static 
discharge. It should be noted;, however, that the current 
shown is not a measure of the true current, as the oscillo- 
graph cannot respond to currents of such high frequency. 

It should be here explained that the oscillograph is a 
device consisting of a galvanometer of strong field and high 



Lightning Arresters 1341 

frequency of vibration^ and is used for recording waves of 
alternating current. 

This arrester is designed to operate across 2^200 volts. 
It is used^ however^ from each line to ground^ giving^ thus 
connected^ sufficient protection, and being always able to 
handle a discharge when one line is grounded. It is built 
to be used single-pole, but by placing two or three in the 
same box, becomes double-pole or triple-pole. 

A^C7X//77U/?7 




CcyrnGnC /n >S/7unt /^G3/3tc7nc<s 



^^^ Stc?t/a D/sc/7C7rj^<5 



'3200 l^o/ti 




Fig. 632 
oscillograph curves showing lightning arrester action 

The 1,000-volt arrester is the same in design, but has 
only one gap between the high resistance rod and line. 

The 3,000-volt arrester (see Fig. 633) is based on the 
same general principle as the 2,200-volt arrester, differing 
ifrom it mainly in having two additional gaps to take care 
of the higher voltage. 



1342 



Steam Engineering 



The 2^200-volt arrester (Fig. 634) is used in various 
combinations to form arresters of higher voltage. 

Loiu-Voltage Lightning Arresters. — For low-voltage, 
alternating-current circuits up to 300 volts the lightning 
arrester shown in Fig. 635 is used. This type meets the 
requirements for the protection of low voltage circuits such 



LINE 




GROUND 

Fig. 633 
form f2, 3,000-volt multigap arrester for stations 

as transformer secondaries, motors, series arc lamps, etc. 
These arresters are made in single, double and triple-pole 
units. 

Protection of Cable Systems. — It is frequently necessary, 
and desirable for circuits to dip underground when passing 
through cities, under rivers, etc., and in these cases some 



Lightning Arresters 



1343 



form of metal covered cable is generally used. Eesonance 
invariably produces high potentials at the junction of over- 
head^ and underground lines, and these potentials are often 
of sufficient value to break down the insulation of the 
cables^, and also the insulation of apparatus installed on 
the system. 




Fig. 634 

2,200-volt, form fl, lightning arrester, discharging and 

shunting the dynamic current 



^^x:::««:; 



Fig. 635 
single-pole arrester 



Whenever lines contain both inductance, and capacity 
in appreciable quantities, high voltages, which endanger 
the insulation of the whole system, and which it is impossi- 
ble to detect on ordinary switchboard instruments may 
exist. Abnormal voltages are therefore often found in cir- 



1344 . Steam Engineering 

cuits containing a combination of underground^ and over- 
head circuits and in underground transmission lines. 

Constant Current Arresters. — For constant current 
lighting circuits, horn arresters with resistances are recom- 
mended. It is advisable to place these arresters in the 




^^^^^^^^ 




Fig. 636 
double-pole and triple-pole 300-volt arresters 

station on each outgoing line. When cables are used, the 
arrester should be placed on the pole where the cable joins 
the overhead wires. Fig. 637 shows the appearance of a 
horn lightning arrester. 

Disconnecting Switches.— A AgMjiing arresters with dis- 
connecting switches are desirable in order that they may be 



Lightning Arresters 1345 

disconnected from the line for proper inspection^ adjust- 
ment, cleaning, etc., without opening the line circuit. 

The disconnecting switches, except the 2,500-volt 
switches, are of the post insulator type. The 2,500-volt 
switches are single-blade, front connected, and are mounted 
directly on marble bases. The post insulator switches are 
arranged for mounting on flat surfaces. 




Fig. 637 
horn arrester for constant curren^t circuits 

Choke Coils, — The proper selection of choke coils is an 
important feature of lightning protection. Choke coils 
should be used with lightning arresters except, when the 
arresters are used to protect cable systems. 

Three types of choke coils are shown in Figs. 639 and 
640. The 4,600-volt coil is made of insulated wire, wound 
on wooden core supported by iron feet. The 6,000-volt 
coil is made of insulated wire and is mounted on marble 



1346 



Steam Engineering 



base. For voltages above 6^000 the ^^hour glass^^ type with 
air insulated turns is used. With this t3^pe the coil is 
mounted on a wooden^ slate or marble base. 




Fig. 638 
post type insulator disconnecting switch 




Fig. 639 
hour glass type — choke coil 15,000-35,000 volts 




6,000 VOLTS 4,600 volts 

Fig. 640 

low voltage CHOKE COILS 

The "hour glass'^ type has the following advantages on 
high voltages. 



Lightning Arresters 1347 

1. Should there be any arcing between adjacent tnrns, 
the coils will reinsnlate themselves after the discharge. 

2. They are mechanically strongs and sagging is pre- 
vented by tapering the coils toward the center turns. 

3. The insulating supports can best be designed for the 
strains that they have to withstand. 

In providing lightning arresters the following points 
should be considered: 

1. What is the normal line to line voltage? 

2. How many sets of transmission lines are there ? 

3. Is the system single-phase^ two-phase^ or three- phase; 
or three-phase, four wire? 

4. Is the system delta connected; Y connected, neutral 
non-grounded; or Y connected, neutral grounded? 

5. If single-phase, is the neutral grounded? 

'6. Are switches to be furnished with the arrester? 

7. If so, are they to be double-blade or single-blade? 

8. If double-blade switches are required, state the cur- 
rent-carrying capacity of the line switch. 

9. Are choke coils to be furnished? If so, state their am- 
pere capacities and the number desired. 

10. The number of switch hooks to be furnished. 

11. If the line is partly overhead, and partly under- 
ground, submit a rough sketch that shows where the un- 
derground portion is located with reference to the stations 
and the remainder of the line. 

DIRECT CURRENT LIGHTNING ARRESTERS. 

The Type M Form D-2 arrester (Pig. 641) has been 
the standard for direct current circuits for several years, 
and is furnished for lighting and power circuits of from 
60 to 375 volts, and for railway and power circuits of from 
250 to 1,800 volts. 



1348 Steam Engineering 

The present form of arrester is somewhat longer and 
narrower than the earlier types^ and the spark gap^ and 
non-inductive resistance are in a straight line, thus form- 
ing a direct path for the discharge, and reducing to a mini- 
mum the possibility of short circuit in the box in case of 
excessively heavy lightning discharges. One of the valuable 
features of the MD-2 arrester is the fact that all parts can 
be readily inspected on removing the cover of the porcelain 
enclosing box (Fig. 642) and a glance will show if the 
arrester is in proper condition for the next storm. The 




Fig. 641 
direct current arrester, type m, form d-2 

gap is surrounded by a strong electro-magnet, which im- 
mediately blows out the dynamic arc through the chute after 
the lightning discharge has passed. 

The gaps on arresters up to 850 volts are adjusted to , 
.025 inch, and on higher voltages to .094 inch. These ar- 
rangements have been found to afford excellent protection 
to the insulation of the equipments, due to the low break- 
down points. 

The spark gap terminals, are threaded, and attached to 
the lid of the box, thus affording a ready method of ad- 



Lightning Arresters 



1349 



justment^ positive grip on the terminals^ and easj^ access 
for examination. 

Ground Connections. — In all lightning arrester installa- 
tions it is of utmost importance to make perfect ground 
connections, as a large majority of lightning arrester troubles 
can be traced to the lack of this precaution. It has been 
customary to ground a lightning arrester by means of a 




Fig. 642 
direct current lightning arrester- 



INTERIOR 



large metal plate buried in a bed of charcoal, at a depth 
of six or eight feet in the earth. 

A more satisfactory method of making a ground is to 
drive a number of 1-inch iron pipes six or eight feet into 
the earth at several points about the station, connecting 
all these pipes together by means of copper wii'e or pref 
erably copper strip. A quantity of salt should be placed 



1350 



Steam Engineering 



around each pipe at the surface of the ground and the 
ground thoroughly moistened with water. It is advisable 
to connect the pipes to the iron frame work of the station. 




Fig. 643 

HORN GAP INSTALLATION FOR 35,000 VOLT ALUMINUM LIGHTNINa 

ARRESTERS, SCHENECTADY POWER CO., SHOWING ROOF 12^^- 

TRANCES TO STATION AND WALL ENTRANCES TO LIGHTNING 

ARRESTER TOWER. ONE SET OF ARRESTERS 

DISCONNECTED 



Lightning Arresters 1351 

and also to any water mains^ metaL flumes, or trolley rails 
that are available. 

For the station of ordinary size the following recommen- 
dation is made. Place three earth-pipes equally spaced near 
each outside wall, making twelve altogether, and place 
three extra pipes spaced about six- feet apart at a point 
nearest the arrester. 

When plates are placed in streams of running water, it 
is much better for them to be buried in the mud along the 
bank, than to lie in the stream. Streams with rock}^ bot- 
toms are to be avoided except as a last resort. 

Whenever plates are placed at any distance from the 
arrester it is advisable to drive a pipe in the earth directly 
beneath tiie arrester, thus making the ground connections 
as short as possible. Earth plates at a distance cannot be 
depended upon. Long ground wires in a station cannot be 
depended upon, unless a lead is carried to the multiple pipe- 
earths described above. 

In view of the fact that it is advisable to occasionally 
examine the ground connections to see that they are in 
proper condition, it is desirable to' lay out the exact plans 
of the location of the ground plates, ground wires, or pipes, 
with a brief description of them, so that at any time the 
data may be referred to. 

From time to time the resistance of the ground connec- 
tions should be measured to determine their condition. This 
is very easily done when pipe grounds are installed, as the 
resistance of one pipe can be accurately determined, when 
three or more pipes are used. The resistance of a single 
pipe ground in good condition has an .average value of 
about 15 ohms. A simple and satisfactory method of keep- 
ing account of the condition of the earth connections is to 
divide the pipe-earths into two groups, and connect each 



1352 Steam Engineering 

group to the 110- volt lighting circuit, with an ammeter in 
series. If there is a flow of about 20 amperes the condi- 
tions are satisfactory, provided the pipe-earths are properly 
distributed around the station. 

ALUMINUM LIGHTNING ARRESTERS. 

The design of the aluminum arrester is based on the 
characteristics of a cell consisting of two aluminum plates 
on which has been formed a film of hydroxide of aluminum, 
immersed in a suitable electrolyte. This film is formed on 
the aluminum plates by a series of chemical and electro- 
chemical treatments at the factory. 

Valve Action, — Up to a certain critical voltage this hy- 
droxide film has the property of insulating, or rather op- 
posing the flow of current and is, therefore, closely analo- 
gous to a counter-electromotive force. Up to this critical 
voltage only a small leakage and charging current can 
flow, but drring any rise above this voltage the current 
flow through the cell is limited only by the actual resistance 
of the electrolyte, which is very low. The action is com- 
parable to that of the well-known safety valve of a steam 
boiler by which the steam is confined until the pressure 
rises to a given value, at which point the valve opens and 
releases the excess pressure. This action of the aluminum 
cell is also closely analogous to that of a storage battery on 
direct current. Up to about two volts per cell, impressed, 
the storage battery, when charged, opposes an equal counter- 
electro-motive force, shutting off the flow of current ; but 
for voltage above ,this value the current is limited only by 
the internal resistance of the cell. This characteristic 
makes the aluminum cell ideal as a means of discharging 
abnormal potentials, or surges in electric circuits. It prac- 



Lightning Arresters 



1353 



tically prevents the flow of current at operating voltages, 
but instantly short circuits such abnormal portions of a 
potential wave^ or surge, as would be dangerous to the in- 
sulation of the system. 





"^ "s^ 


* * *. jj 


^ ■! *, 


1 *" •« .^ 


^^ ^ 


1 








1 


. 


















t^ — — _ _ _ 






" " : :~ 


^ _. _. 




1 








^.'' ^ " - - 




















>. _ _ «. — . » 
















c ^ — ! —-J 



Fig. 644 
volt-ampere characteristic curve of aluminum cell 

A volt-ampere-characteristic-curve of the aluminum cell 
on alternating current is shown in Fig. 644. The data for 
this curve was taken with an oscillograph. It should be 



1354 Steam Engineering 

noted that the critical voltage^ alternating current, is slight- 
ly above 340 volts. This cut gives the discharge rate only 
up to 5 amperes, in order to better illustrate the normal and 
critical voltage points. Above this value the discharge rate 
depends almost entirely upon the internal resistance of the 
electrolyte. This resistance is such that at double the nor- 
mal operating voltage, or 600 volts per cell, the current 
discharge is six hundred, to one thousand amperes for a 
brief time. This rate of discharge represents a quantity of 
electricity several times greater than the quantity liberated 
by an ordinary induced lightning stroke. 

Condenser Action, — Besides the valve action described 
above there is another characteristic of the cell of great im- 
portance. The thin insulating film of aluminum hydroxide 
between the conducting aluminum and the conducting elec- 
trolyte acts as a dielectric and the cell, therefore, is an 
elecstatic condenser. A condenser of this type makes an 
ideal path for high frequency lightning discharges. With 
these arresters, for instance, 10,000 cycles, vrhich is not an 
unusual frequency for lightning disturbances, would dis- 
charge almost 100 amperes without any rise in voltage. 

Due to this capacity, these aluminum arresters cannot 
be connected permanently across alternating voltage. The 
charging current at normal frequency (about .5 amp.) 
would in time heat the electrolyte. In every case, there- 
fore, spark gaps set to arc over at slight increase of voltage, 
insulate the arrester from the line. 

Film Dissolution. — Another characteristic of the alumi- 
num cell is the dissolution of a part of the film when the 
plates stand in the electrolyte, and the cell is disconnected 
from the circuit. The film is presumably composed of two 
parts; one part is hard and insoluble, and apparently acts 
as a skeleton to hold the more soluble part. When a cell. 



Lightning Arresters 



1355 



which has stood for some time disconnected^ is reconnected 
to the circuit, there is a momentary rush of current, which 
replaces the part of the film which has dissolved. All elec- 






Wooden ^ 
Camr 







Cones ■ 
Complete 



Fig. 645 
cross section of aluminum lightning arrester 



trolytes dissolve the film, the extent of the dissolution de- 
pending upon the length of time the film is in the electro- 
lyte, the electrolyte used, and its temperature. It is neces- 



1356 



Steam Engineering 



sary to charge the cells from time to time to prevent the 
initial rush of dynamic current causing trouble. By keep- 
ing the films formed at all times^ the initial rush of cur- 
rent is prevented, and the ultimate temperature rise in case 
of continued discharge of the arrester is minimized. The 
ability of the arrester to take care of discharges lasting for 
any considerable length of time, therefore, depends upon 
the conditon of the arrester film. When the cells, in com- 
mercial use, are allowed to stand for not more than a day 




Fig. 646 

PARTS OF 15000 VOLT ALUMINUM LIGHTNING ARRESTER 

or two, the film dissolution, and initial current rush is 
negligible. Suitable means are provided with the arresters 
for connecting them directly across the line. This is a 
very simple operation, and thus the film is kept in good 
condition. 

In very warm climates it is sometimes advisable to take 
special precaution to keep the cells normally cool. 

Design, — The aluminum lightning arresters for alter- 



Lightning Arresters 



1357 



nating current circuits from 1^000 to 110^000 volts con- 
sist essentially of inverted aluminum cones^ placed one 
above the other in stacks^ and insulated with a vertical spac- 
ing of about .3 inch. An electrolyte partially fills the 



giltfte' ■.:^' .';:; - . — — 


~~ — " — 'mwMskMtiiWMi^m 


._,,.. . 




=..,...^.:..^..,. ^ - 






. 


iii^t^:fl 


4 


ms.s 






4 


^H 


'~V' '^^^BV 


i 


-^ 


\_:|MK 


fy 




r^-' 


U 




1 - 






^SSKKt^^mShL'i. 






§£SM. rM-'--'^ 


^K^ 




^B 


i 




1 


lifiii^M^^^^^^fg^l 


9 





Fig. 647 
parts of 4600 volt three- phase aluminum lightning arrester 

space between adjacent cones^ so forming aluminum cells 
connected in series. The stack of cones with the electrolyte 
between them is then immersed in a tank of oil. The elec- 
trolyte being heavier than the oil remains between the 



1358 Steam Engineering 

aluminum cones. The oil improves the insulation between 
cones^ prevents evaporation of the solution and^ due to its 
heat absorbing capacity^ enables the arresters to discharge 
continuously for long periods, a very valuable feature of 
these arresters. The tanks are of steel with welded seams. 
The general arrangement of the cells is shown in Figs. 
645, 646 and 647. 

QUESTIOI^S AND ANSV^ERS. 

935. How are switchboards made up? 

Ans. They are built up of panels of slate or marble sup- 
ported by frames of angle iron. 

936. How are the different panels designated? 

Ans. Some are for motor control, others for dynamo 
running, others for operating the outer circuit, and others 
for charging storage batteries. ' " ' 

937. Is a knowledge of switchboards an important mat- 
ter? 

Ans. It is, and every engineer should especially study 
those in his own station. 

938. What is the regular equipment of a D. C. switch- 
board having a capacity of from 250 to 6,500 amperes? 

An^s. One carbon-break or magnetic blow-out circuit 
breaker with telltale. 

One illuminated dial ammeter with shunt. 

One hand wheel and chain for operating rheostat. 

One receptacle for voltmeter plug. 

One S. P. S. T. field switch. 

One S. P. S. T. main switch. 

One recording watt-hour meter. 

939. What is meant by the abbreviations S. P. S. T.? 
Ans. Single Pole Single Throw. 



Questions and Answers 1359 

940. What does D. P. D. T. mean in speaking of switch- 
boards ? 

Ans. . Double Pole Double Throw. 

941. What is meant by T. P. ? 

Ans, Triple pole. It opens every circuit of a three- 
phase system. 

942. Is it good practice to place a main switch at the 
machine? 

Ans, It is best. 

943. Why? 

Ans. So that the cables from generator to board may 
be cut off at the generator. 

944. What is an equalizer? 

Ans, It is a cable running along from machine to ma- 
chine^ and connecting the functions of series field and 
brush on all the machines^ but does not connect with switch- 
board. 

945. What kind of a break has the field switch? 
Ans. A carbon break. 

946. Describe the action of a field switch. 

Ans. Just before it opens it makes contact with an extra 
clip, and puts a resistance on as a shunt around the field 
coils. 

947. If this were not done what would be the conse- 
quences ? 

Ans. The fields would act as a spark-coil and the in- 
sulation be damaged. 

948. When it is desired to throw a generator in par- 
allel with other generators already running what is the 
proper method of procedure? 

Ans. First. Close main and equalizer switches near the 
machine. 



1360 Steam Engineering 

Second. Close field switch on panel. 

Third. Close circuit breaker. 

Fourth. Insert potential plug in receptacle and regulate 
voltage. 

Fifth. When proper voltage is obtained close the other 
main switch on panel. 

949. What is meant by voltage? 
Ans, Electric pressure^ or potential. 

950. What is a volt? 
Ans. The unit of pressure. 

951. What is a voltmeter? 

Ans. An instrument that indicates the voltage. 

952. What is an ohm? 
Ans, The unit of resistance. 

953. Give a brief definition of Ohm^s law? 

Ans. The electromotive force equals the resistance mul- 
tiplied by current intensity. 

954. What is an ampere? 

Ans. It is the unit of volume, or quantity-time unit for 
measuring the rate of flow of an electric current. 

955. What is a coulomb? 

Ans. It is an ampere-second. A coulomb equals the 
flow of an ampere of current past a given point each second 
of time. 

956. What is an ammeter? 

Ans. An apparatus for measuring current rate. 

957. What is the meaning of the word watt as used 
in electrical work? 

Ans. A watt is the unit of work. It equals volts X am- 
peres. 

958. What is the function of the wattmeter? 
Ans. To record the watt-hours of work. 



Questions and Ancwers 1361 

959. What is a kilo watt (K. W.) ? 
Ans. 1,000 watts. 

960. Expressed in mechanical horse-power, what is one 
K. W. equal to ? 

Ans. 1000-^ 746=1 1/3 H. P. 

961. What is a field rheostat? 

Ans. An apparatus for controlling the current output. 

962. What is the function of a transformer? 

Ans. To transform the current from a higher to a lower 
voltage, or from A. C. to D. C. 

963. What is meant by synchronism of electric ma- 
chines ? 

Ans. When the maximum value of the E. M. F. in 
each machine occurs at exactly the same instant of time, 
the machines are in synchronism. 

964. What is meant by the exciter panel of a switch- 
board ? 

Ans, It is the panel that is equipped with the necessary 
switches, etc., for connecting the small exciter dynamo with 
the other generators in the station. 

965. What is a sub-station? 

Ans. It is the connecting link between the transmission 
line, and the trolley wire or third rail. 

966. When A. C. is generated at the power station, and 
D. C. is used on the line, how is it accomplished? 

Ans. The A. C. is changed to D. C. by rotary converters 
lat the sub-station. 

967. What is meant by frequency? 

Ans. The number of times the current reverses per sec- 
iond. 

968. What is the usual frequency for railway motors? 
Ans. 25 is the standard. 

969. What is a frequency changer? 



1362 Steam Engineering 

Ans. A machine which receives current at one frequency 
and delivers it at another frequency. 

970. What apparatus is used in an A. C. to D. C. sub- 
station ? 

Ans, Step down transformers^ rotary converters^ and 
A. C. incoming and D. C. outgoing switchboards. 

971. What is the proper procedure for placing rotary 
converters in service ? 

Ans. After the machine has been started from the A. 
C. ends, and builds up with the proper polarity, first close 
the equalizer switch (on machine) — second, close circuit 
breaker on panel — third, insert potential plug in receptacle 
and regulate voltage — fourth, when the proper voltage is 
obtained, close positive switch (on panel). 

972. What will be the result if the rotary builds up with 
polarity reversed ? 

Ans. The voltmeter will swing back of zero. 

973. How may the polarity be corrected? 

Ans. By means of the four-pole, double-throw field 
break-up reversing switch mounted on the converter. 

974. Describe an oil switch. 

Ans. It is a switch similar in its action to other 
switches, with the exception that its mechanism is im- 
mersed in a small tank of oil. 

975. What advantage is gained thereby? 

Ans. Eeliability of action in opening or closing a cir- 
cuit. 

976. Mention another advantage gained by the use of 
the oil switch and oil circuit breaker. 

Ans. It has made safely possible the transmission and 
use of high-tension currents of electricity. 

977. What is a circuit -breaker? 

Ans. It is a switch so designed as to be capable of fre- 



Questions and Answers 1363 

quently opening the circuit carrying its full current with- 
out any damage to itself. 

978. What is a galvanometer? 

Ans. An instrument consisting of a coil of wire car- 
rying the current to be tested^ and a magnet, the two be- 
ing arranged so that one can be deflected. 

979. Describe the Thompson type of galvanometer. 
Ans, The coil of wire is stationary, and the light mag- 
netic needle is suspended by a silk thread. 

967. Describe the D^Arsonval galvanometer. 

A71S. In this type the small light coil of wire is sus- 
pended by a fine bronze wire between the poles of a station- 
ary magnet. 

968. How are the readings taken from these instru- 
ments ? 

Ans, From a circular scale, over which the needle of 
the instrument swings. 

980. What is a lightning discharge? 
Ans, An equalization of potential between the earth, 

and either clouds, or saturated atmosphere. 

981.' What path does the discharge generally follow? 
Ans, The path of least resistance. 

982. What are the general requirements for protection 
of .electric stations from lightning ? 

Ans. The supplying of paths to ground for any charge 
which might accumulate on lines or machinery. 

983. What is the general theory of the multi-gap light- 
ning arrester? 

Ans. When voltage is applied across a series of multi- 
gap cylinders, the voltage distribution is not uniform, but 
is governed by the capacity of the cylinders, both between 
themselves, and also to ground, which results in the con- 
centration of voltage across those gaps nearest the line. 



1364 Steam Engineering 

984. What are the principal elements of a 600 volt 
D. C. aluminum lightning arrester? 

Ans. Two concentric aluminum plates immersed in an 
electrol3^te contained in a glass jar, the outside plate of 
each cell being positive, and the inner one negative. 

985. Describe the multigap lightning arrester for A. C. 
Ans. It consists of a series of spark gaps shunted by 

graded resistances, but without series resistance. 

986. Describe briefly the aluminum lightning arrester. 
Ans, It consists of two aluminum plates on which has 

been formed a film of hydroxide of aluminum, immersed 
in a suitable electrolyte. 



Current Distribution 

a 

Divided Circuits, — Currents of electricity^ although they 
have no such material existence as water or steam, still 

^ obey the same general law ; that is, they flow and act along 
the lines of least resistance. If a pipe extending to the 
top of a ten-story building had a very large opening at the 

- first floor, it would be impossible to force water to the 
top floor. All the water would run out at the first floor. 
If the opening at the first floor were small only a part of 
the water would escape through it, some would reach the 
top of the building. The flow of water in each case is in- 



FiG. 648 

versely proportional to the resistance offered to it by the 
dijfferent openings. 

The same thing is true of currents of electricity. Where 
several paths are open to a current of electricity the flow 
through them will be in proportion to their conductivities, 
which is the inverse ratio of their resistances. As an illus- 
tration, the current flow through all of the lamps. Fig. 

648, is the same, because each lamp offers the same re- 
sistance. But if we arrange a number of lamps as in Fig. 

649, the lampsi in series will offer twice as much resistance 
as the single lamps, and will receive but half the current 
of the single lamp. In Fig. 650 we have still another 

1365 



1366 



Steam Engineering 



arrangement. The lamp A limits the current which can 
flow through B and C^ and that current which does flow 
divides between B and C in proportion to their conductivi- 
ties. If B has a resistance of 110 ohms and C 220 ohms^ 
then B will carry two parts of the current and^ C only one. 
The combined resistance of all lamps^ Fig. 648^ equals the 
resistance of one lamp divided by the number of lamps. 
The combined resistance, Fig. 649, equals the sum of the 
resistances of the two lamps at A, multiplied by the resist- 



A, 



OB 



Fig. 649 




Fig. 650 



ance of B and divided by the sum of all the resistances. If 

the resistance of each of the lamps were 110 ohms, the 

problem would work out thus : 

110+110X110 

' =73 1/3 

110+110+110 ^ * 

In Fig. 650 the total resistance is 

110X220 

[-110=183 1/3. 

110+220 

One practical illustration of the above law may be found 

in the method of switching series arc lamps, Fig. 651. As 



Current Distribution 



1367 



long as the switch S is open the arc lamp burns^ bnt as soon 
as the switch is closed the lamp is extinguished because 
the resistance of the short wire and the switch S is so 
much less than that of the arc lamp that practically all 
the current flows through S. 

Wiring Systems. — The system of wiring which is most 
generally used for incandescent lighting and ordinary pow- 
er purposes is called the two-wire parallel system. In this 
system of wiring the two wires run side by side^ one of 
them being the positive and one the negative. The lamps, 
motors and other devices are then connected from one wire 
to the other. A constant pressure of electricity is main- 




FiG. 651 



tained between the two wires, and the number and size of 
lamps, or other apparatus, connected to these two wires, 
determine how many amperes are required. Each lamp or 
' motor is independent of the others and may be turned 
on or off without disturbing the others. 

A diagram of such a system is shown in Fig. 652. 

In this system the quantity of current varies in propor- 
tion to the number of devices connected to it. Suppose 
that we are maintaining a pressure or potential or electro- 
motive force of 110 volts on such a system, and that we 
have connected to the system ten 16 candle power incan- 
descent lamps, consuming one-half ampere each. The total 



1368 



Steam Engineering 



quantity of current to supply these lamps would be 5 am- 
peres. If we should now switch on ten more lamps the 
quantity of current would be 10 amperes^ and the pressure 
would remain 110 volts. This system is also known as the 
"constant potential system/^ or multiple arc system^ and 
among the numerous devices used in connection with it are 




Fig. 652 
two-wire parallel system 

the constant potential arc lamp^ the shunt motor, the com- 
. pound wound motor, the series motor, incandescent lamps, 
etc. Electric street railways are also operated on this sys- 
tem. The current supplied through this system of wiring 
may be either direct or alternating current. 

The series arc system. Fig. 653, is a loop; the greatest 
electrical pressure being at the terminal, or terminal ends 




-^ 



Fig. 653 
series arc system 

of the loop. The current in such a system of wiring is 
constant, and the pressure varies as the lamps or other 
apparatus are inserted in or cut out of the circuit. This 
system is also called the constant current system. The same 
current passes through all of the lamps, and the different 
lamps are also independent of each other. 



Current Distribution 



1369 



At the present time the series system is used mostly for 
operating high tension series arc lamps. The use of motors 
with it has been almost entirely abandoned. 

The series multiple system, Fig. 654, is simply a number 
of multiple systems placed in series. This method of wiring 




Fig. 654 

SERIES MULTIPLE SYSTEM 

was at one time employed to run incandescent lights from 
a high tension series arc light circuit, but on account of the 
danger connected with the use of incandescent lamps, op- 
erated from a high tension arc lamp circuit, the system has 
been abandoned. It is not approved by insurance compa- 
nies, and consequently is not often used. 




Fig. 655 
multiple series system 

The multiple series system consists of a number of small 
series circuits, connected in multiple, as shown in Fig. 655. 
This system of wiring is used on constant potential sys- 
tems, where the voltage is much greater than is required by 
the apparatus to be used^ as, for instance, connecting eleven 



1370 



Steam Engineering 



miniature lamps^ whose individual pressure required is 10 
volts^ into a series^ and then connecting the extreme ends of 
such a series to a multiple circuit whose pressure is 110 
volts. 

The three wire system^ Fig. 656, is a system of multiple 
series. In this system, as its name implies, three wires are 
used, connected up to the machines in the manner shown 
in the diagram. Both machines are in series when all 
lights are turned on, but should all lights on one side of 
the neutral or center wire be turned off the machine on 
the other side alone would run the other lights. 

One of these wires is positive, the other is negative, and 
the remaining one or center wire is neutral. In ordinary 




:-^ 'i A i i i i 



^ -9 ? 9 9 9 9 



Fig. 656 

THREE WIRE SYSTEM 

practice from positive to negative wire, a potential of 220 
volts is maintained, while from the neutral wire to either 
of the outside wires a potential of 110 volts exists. The 
advantages of such a system are many, principally among 
them is the use of double the voltage of the two wire sys- 
tem; this reduces the current one-half and allows the use 
of smaller wires. This system only requires three wires 
for the same amount of current that would require four in 
the other system. Motors are supplied at 220 volts, while 
lights operate at 110. Incandescent lighting circuits can 
be maintained from either outside wire to the neutral wire. 
The saving in copper by dispensing with the fourth wire 



I 



Curfent Distribution 1371 



is not the only advantage in the saving of conductors. The 
neutral wire may be much smaller than the outside wires 
because it will seldom be called upon to carry much cur- 
rent. 

Inside of buildings^ however^ where overheating of a 
wire is always dangerous^ the neutral wire should be of 
the same size as the others. By tracing out the circuits in 
Fig. 656^ it will readily be seen that, so long as all lamps 
are burning, the current passes out of dynamo 1 into the 
positive wire and from there through the lamps (always 
two in series) to the negative or — wire, returning over it 
to the — pole of dynamo 2. So long as an equal number 
of lamps is burning on each side of the neutral, no current 
passes over the neutral wire in either direction. But if the 
positive or + wi^^ should be broken, say at a, dynamo 1 
will no longer send current and the lamps between the posi- 
tive and neutral wire will be out. 

Dynamo 2 will now supply the lamps between the neutral 
and the negative wire and for the time being the neutral 
wire will become positive. Should the negative wire break 
at b, the lamps connected to it would be out and dynamo 1 
would supply the lights on its side, the neutral wire be- 
coming negative. When motors of one or more horse-power 
are used on this system, it is usual to connect them to the 
outside wires using 220 volts. It is important also to ar- 
range the wiring so that an equal number of lights are in- 
stalled on each side of the neutral. When the lights and 
motors are so arranged, the system is said to be "balanced.^^ 
It is also very important to arrange so that the neutral 
wire cannot readily be broken. Should the neutral wire be 
opened while, for instance, fifty lamps were burning on one 
side and say ten or twenty on the other, the ten or twenty 
would be broken by the excess voltage. Grounded wires 



1372 



Steam Engineering 



ordinarily cause more trouble than anything else on elec- 
tric light or power circuits^ but with the three wire system, 
the neutral wire is often grounded. Grounds on this wire 
are less objectionable than on other wires, because it car-* 
ries very little current, and that current is constantly vary- 
ing in direction, so that no great amount of electrolysis 
can occur at any one place. 

Feeders. — (See Fig. 657), as the name implies, is a 
term used to designate wires which convey the current to 



Seruice 




.NWWWW NS\\\s\\v\NX\SN^-y\^^S^V:?^^\\^^ 



5 p^ ^^^^^^:^^^^^^^^^^^^^^^^^^^^^^^^^^^ 



Branch 
SuUdin^ mams 




, ^VvN- > , 






Fig. 657 

any number of other wires, and the feeders become a part 
of the multiple series, multiple and three wire systems. 

Distributing mains are the wires from which the wires 
entering buildings receive their supply. 

Service wires are the wires that enter the buildings. 
■ The center of distribution is a term used for that part 
of the wiring system from which a number of branch cir- 
cuits are fed by feeder wires. In most buildings the tap 
lines are all brought to one point, and terminate in cut-out 
boxes. These cut-out boxes are supplied by the main. Each 
floor of the building may have a cut-out box, or each floor 



Current Distribution 



1373 



of the building may have several cut-out boxes of the above 
■iescription. 

I Calculation of ^Yires. — If we desire to transmit or deliver 
-a certain quantity of liquid through a pipe, we estimate the 
-size of the pipe and the comparison of sizes in the pipes by 
Squaring the diameter, in inches, and multiplying the re- 
;ult by the standard fraction .7854. By way of explanation 
^ve will dwell upon the above method for a short time. In 
<Fig. 658 we have a surface which measures one inch on all 
four sides, and which has an area of one square inch. 

Wow in a circle which is contained in this figure, and 
which touches all four sides of the square, we would only 




Fig. 658 

have .7854 of a square inch. If the diameter of this circle 
is 2 inches instead of 1, you can readily see by Fig. 659 
that its area is four times as great or 2X^=4. We then 
multiply by the standard number .7854 in order to find the 
area contained in the two-inch circle; and if the diameter 
were 3 inches, then 3X3=9, and 9X.'^854 would be the 
area in square inches contained in the three-inch circle. 

Again, if we had a square one inch in area, like Fig. 660, 
and we took one leg of a carpenter'^, compass and placed it 
on one corner of this square, striking a quarter-circle from 
one adjacent corner to the other adjacent corner, the area 
inscribed by the compass would again be .7854 of a square 
inch. 



1374 



Steam Engineering 



The above will explain to the reader the relation between 
the circular and square mil. The circular mil is a circle 

1 

one mil ( of an inch) in diameter. The square mil 

1,000 

is a square, one mil long on each side. In the calculation 

of wires for electrical purposes, the circular mil is generally 

used, because we need only multiply the diameter of a wire 



Fig. 659 

by itself to obtain its area in circular mils. If we used 
square mils we should have to multiply by .7854. 

The resistance of a conductor (wire) increases directly 
as its length, and decreases directly as its diameter is in- 
creased. A wire having a diameter of one mil and being 
one foot long has a resistance at ordinary temperature of 
10.7 to 10.8 ohms. 10.8 ohms is the resistance usually 
taken. If this wire were two feet long, it would have 
a resistance of 21.4 ohms, but if it were two mils in diam- 
eter and one foot long, it would have a resistance one- 
fourth of 10.7, or about 2.67. 



Current Distribution 



1375 



Every transmission of electrical energy is accompanied 
by a certain loss. We can never entirely prevent this loss 
any more than we can entirely avoid friction. But we can 
reduce our loss to a very small quantity simply by selecting 
a very large wire to carry the current. This would be the 
proper thing to do if it were not for the cost of copper^ 
which would make such an installation very expensive. As 
it is^ wires are usually figured at a loss of from 2 to 5 
per cent. 

The greater the loss of energy we allow in the wires, 
the smaller will be the cost of wire, since we can use smaller 
wires with the greater loss. 




Fig. 660 

In long distance transmission and where the quality of 
light; is not very important, a loss of 10 or 20 per cent is 
sometimes allowed, but in stores, residences, etc., the loss 
should not exceed 2 or 3 per cent, otherwise the candle 
power of the lamps will vary too much. 

Where the cost of fuel is high the saving in first cost of 
copper is soon offset by the continuous extra cost of fuel 
to make up for the losses in the wires. 

To determine the size of wire necessary to carry a certain 
current at a given number of volts loss, we may proceed in 
the following manner : Multiply the number of feet of wire 
in the circuit by the constant 10.7, and it will give the 
circular mils necessary for one ohm of resistance. Multiply 



1376 Steam Engineering 

this by the amperes^, and this will give the ciicular mils 

for a loss of one volt. Divide this last result by the volts 

to be lost, and the answer will be the number of circular 

mils diameter that a copper wire must have to carry the 

current with such a loss. After obtaining the number of 

circular mils required, refer to table 53 and select the wire 

having such a number of circular mils. 

The formula is as follows : 

Feet of wireXlO-'^Xaniperes 

• =circular mils. 

Volts lost 

By simply transposing the above terms we obtain an- 
other formula, which can be used to determine the volts 
lost in a given length of wire of a certain size, carrying a 
certain number of amperes. 

The formula is as follows : 

Feet of wireX 10.7 X amperes 

; ^ =: Volts lost. 

Circular mils 

And again, by another change in the terms we obtain a 

formula which shows the number of amperes that a wire 

of given size and length will carry at a given number of 

volts lost : 

Circular mils X volts lost 

— = Amperes. 

Feet of wireXlO.7 

In computing the necessary size of a service or main 

wire, to supply current for either lamps or motors, it is 

necessary to know the exact number of feet from the 

source of supply to the center of distribution. When the 

distance of center of distribution is given it is well to 

ascertain whether it is the true center or not. It may be 

only the distance from a cut-out box that has been given, 

when it should have been the distance from the point at 

which the service enters the building or, perhaps from the 



Current Distribution 1377 

point at which the service is connected to the street mains. 
For when the size is determined it is for a certain loss 
which is distributed over the entire length of the wire to 
be installed. The transmission of additional current on 
the mains in the building increases the drop in volts in 
the main, and likewise in the service. Most buildings are 
wired for a certain per cent loss in voltage, estimated from 
the point where the service enters the building. All addi- 
tions should be estimated from that point. 

In using the formula for finding the proper size wire 
to carry current, the first thing to be determined is the 
length of the wire; remember that the two wires are in 
parallel, and therefore the total length of the wire is twice 
the total distance from the commencement to the end of 
the circuit. If the proposed load on this circuit is given 
in lamps, you may reduce it to amperes, and if the pro- 
posed load is given in horse-power, you may reduce it to 
amperes. The voltage on the circuit is known in either 
case. You take the loss of the voltage and divide the pro- 
duct of amperes, multiplied by the length, as found, and 
10.7 by it; this answer will be the size in circular mils of 
a wire necessary to carry the amperes. 

Example.— What is the size of wire required for a 50- 
volt system, having 100 lamps at a distance of 100 ft., with 
a 4 per cent loss? 

Answer.— The load of 100 lamps on a 50-volt system is 
100 amperes, and a 4 per cent loss of 50 volts is 2 volts. 
Multiply the total length of the wire, which is twice the 
distance, or 200 feet, by the 100 amperes of current; this 
gives us 20,000. Then multiply this by the constant, which 
is 10.7; this gives us 214,000. Divide this by 2, which is 
the loss in volts, and you have 107,000 circular mils diam- 
eter of wire required. 



13.78 Steam Engineering 

When determining the size of wire to be used it is al- 
ways necessary to consult the table of carrying capacities^ 
and this will verv often indicate a wire much larorer than 
that determined by the wiring formula^ especiall}^ if a some- 
what high loss is fignred on. 

When estimating the distance it is not always correct to 
take the total distance. 

To illustrate: Suppose one lamp is 100 feet from the 
point at which the distance is determined^ and the farthest 
lamp is 400 feet^ the remaining lamps being distributed 
evenly between these two points^ we would average the 
distances between the first and last lamp^ which would be 
200 feet. It is necessary to use judgment in estimating the 
mean or average distance^ as the lamps or motors are 
bunched differently in each case. 

In a series system the loss in voltage makes considerable 
difference to the power, but does not affect the quality of 
the light as much as in a multiple arc or parallel system. 
In a parallel system the lamps require a uniform pressure, 
and this can only be had by keeping the loss low. In a 
series system the lamps depend upon the constant current 
and the voltage varies with the resistance, in order to keep 
the current constant. This is accomplished by a regulator 
on the dynamo, which is designed to compensate for the 
changes of resistance in the circuit and to increase or de- 
crease the pressure as required. 

In estimating the size of wire for a series system you 
consider the total length of the loop. There is no average 
distance as the total current travels over the entire circuit. 
We will assume that you have an arc light circuit of a 
No. 6 Brown & Sharp gauge wire, and want to find what 
loss there is in this circuit-. You have the area of a No. 6 
wire, which is 26,250 circular mils, and the length of the 



Current Distribution 1379 

circuit;, and from this we will figure the loss in this manner : 
Assuming the circuit to be 10,000 feet long, and the cur- 
rent 10 amperes, we will multiply 10,000 feet by 10 am- 
peres, and this by 10.7, which gives us 1,070,000, and divide 
this by 26,250. The answer is 40 volts, lost in the circuit. 

Such a circuit would operate at perhaps 2,000 or 3,000 
volts, and a loss of 40 v^olts would not be excessive. It 
would be wasting a little less energy than is required to 
burn one large arc lamp. 

The multiple series system is a number of small wires 
connected in multiple, and is the same as the multiple are 
or parallel system. The .wire is figured in the same way as 
for the multiple arc system. 

The series multiple system is a number of small parallel 
systems, and these are connected in series by the main wire. 
The wire is figured the same as for the series system. 

The Edison three-wire system, is a double multiple, and 
the two outside wires are the ones considered when carrying 
capacity is figured. When this system is under full load 
or balanced, the neutral wire does not carry any current, 
but the blowing of a fuse in one of the outside wires may 
force the neutral wire to carry as much current as the out- 
side wire and it should, therefore, be of the same size. The 
amount of copper needed with this system is only three- 
eighths of that required for a two-wire system. 

Wiring Tables. — On the following pages are presented 
wiring tables 55, 56 and 57 for 110,220 and 500 volt work. 
These tables are used in the following manner : Suppose we 
wish to transmit 60 amperes a distance of 1,800 feet at 110 
volts and at a loss of 5 per cent. We take the column 
headed by 60 in the top row and follow it downward until 
we come to 1,800, or the number nearest to it. From 
this number we now follow horizontally to the left, and 



1380 Steam Engineering 

■iiiider the column headed by 5 we find the proper size of 
wire, which is 500,000 c. m. The same current, at a loss 
of 10, would require only a 0000 wire, as indicated under 
the column at the left, headed by 10. 

Before making selection of wire, always consult table 53 
of carrying capacities. This table is taken from the rules 
of the National Board of Fire Underwriters, and is in gen- 
eral use. 

The first three of the following tables are wiring tables 
for the three standard voltages, 110, 220, 500. From these 
tables can be found the sizes of wire required to carr}^ va- 
rious amounts of current (in amperes) different distances 
(in feet) at several percentages of loss, or the distance the 
different sizes of wire will carry various amounts of cur- 
rent at several percentages of loss can be found. 

These tables are figured on safe carrying capacity for the 
different sizes of wire. The distances in feet are to the 
center of distribution. 



Current Distribution 1381 



Table 53 
carrying capacity of pure copper wires. 

(Underwriters' Rules.) 

"""" Table A. Table B. 

Rubber Other 

Insulation. Insulations. Circular 

B. & S. G. Amperes. Amperes. Mils. 

18 3 5 1,624 

16 6 8 2,583 

14 12 16 4,107 

12 17 23 6,530 

10 24 32 10,380 

8 33 , 46 16,510 

6 46 65 26,250 

5 54 77 3^,100 

4 65 92 41,740 

3 76 110 52,630 

2 90 131 66,370 

1 107 156 83,690 

127 , 185 105,500 

00 150 220 133,100 

000 177 262 167,800 

0000 210 312 211,600 

Circular Mils. 

200,000 200 300 

300,000 270 400 

400,000 330 500 

500,000 390 590 

600,000 450 680 

700,000 500 760 

800,000 550 840 

900,000 600 920 

1,000,000 650 1,000 

1,100,000 690 1,080 

1,200,000 730 1,150 

1,300,000 770 1,220 

1,400,000 810 1,290 

1,500,000 850 1,360 

1,600,000 890 1,430 

1,700,000 930 1,490 

1,800,000 970. 1,550 

1,900,000 1,010 1,610 

2,000,000 1,050 1,670 



The lower limit is specified for rubber-covered wires to 
prevent gradual deterioration of the high insulations by 
the heat of the wires, but not from fear of igniting the 
insulation. The question of drop is not taken into consid- 
eration in the above tables. 



1382 



Steam Engineering 



Table 54 
dimensions of pure copper wire. 







Area. 


Weight and Length. 












Sp. Gr. 8.9 




c/5 


CO 


«5 








oa 




§ 


S 


(U (U 


u 


u 

<u 

ft 


pq 




s 


D 


Q,^ 


ft 


s 

S 




;-i 






'6 


d 






31 


^1 


0000 


460.000 


211600.0 


166190.2 


640.73 


3383.04 


1.56 


000 


409.640 


167805.0 


131793.7 


508.12 


2682.85 


1.97 


00 


364.800 


133079.0 


104520.0 


402.97 


2127.66 


2.48 





324.950 


105592.5 


82932.2 


319.74 


1688.20 


3.13 


1 


289.300 


83694.5 


65733.5 


253.43 


1338.10 


3.95 


2 


257.630 


66373.2 


52129.4 


200.98 


1061.17 


4.98 


3 


229.420 


52633.5 


41338.3 


159.38 


841.50 


6.28 


4 


204.310 


41742.6 


32784.5 


126.40 


667.38 


7.91 


5 


181.940 


33102.2 


25998.4 


100.23 


529.23 


9.98 


6 


162.020 


26250.5 


20617.1 


79.49 


419.69 


12.58 


7 


144.280 


20816.7 


16349.4 


63.03 


332.82 


15.86 


8 


128.490 


16509.7 


12966.7 


49.99 


263.96 


20.00 


9 


114.430 


13094.2 


10284.2 


39.65 


209.35 


25.22 


10 


101.890 


10381.6 


8153.67 


31.44 


165.98 


31.81 


11 


90.742 


8234.11 


6467.06 


24.93 


137.65 


40.11 


12 


80.808 


6529.94 


5128.60 


19.77 


104.40 


50.58 


13 


71.961 


5178.39 


4067.07 


15.68 


82.792 


63.78 


14 


64.084 


4106.76 


3225.44 


12.44 


65.658 


80.42 


15 


57.068 


3256.76 


2557.85 


9.86 


52.069 


101.40 


16 


50.820 


2582.67 


2028.43 


7.82 


41.292 


127.87 


17 


45.257 


2048.20 


1608.65 


6.20 


32.746 


161.24 


18 


40.303 


1624.33 


1275.75 


4.92 


25.970 


203.31 


19 


35.890 


1288.09 


1011.66 


3.90 


20.594 


256.39 


20 


31.961 


1021.44 


802.24 


3.09 


16.331 


323.32 


21 


28.462 


810.09 


636.24 


• 2.45 


12.952 


407.67 


22 


25.347 


642.47 


504.60 


1.95 


10.272 


514.03 


23 


22.571 


509.45 


400.12 


1.54 


8.1450 


648.25 


24 


20.100 


404.01 


317.31 


1.22 


6.4593 


817.43 


25 


17.900 


320.41 


251.65 


.97 


5.1227 


1030.71 


26 


15.940 


254.08 


199.56 


.77 


4.0623 


1299.77 


27 


14.195 


201.50 


158.26 


.61 


3.2215 


1638.97 


28 


12.641 


159.80. 


125.50 


.48 


2.5548 


2066.71 


29 


11.257 


126.72 


99.526 


.38 


2.0260 


2606.13 


30 


10.025 


100.50 


78.933 


.30 


1.6068 


3286.04 


31 


8,928 


79.71 


62.603 


.24 


1.2744 


4143.18 


32 


7.950 


63.20 


49.639 


.19 


1.0105 


5225.26 


33 


7.080 


50.13 


39.360 


.15 


.8015 


6588.33 


34 


6.304 


39.74 


31.212 


.12 


.6354 


8310.17 


35 


5.614 


31.52 


24.753 


.10 


.5039 


10478.46 


36 


5.000 


25.00 


19.635 


.08 


.3997 


13209.98 


37 


4.453 


19.83 


15.574 


.06 


.3170 1 


16654.70 


38 


3.965 


15.72 


12.347 


.05 


.2513 


21006.60 


39 


3.531 


12.47 


9.7923 


.04 


.1993 


26487.84 


40 


3.144 


9.88 


7.7635 


.03 


.1580 \ 


33410.05 



1 mile pure^ copper 



wire tV in. diarn.=13.59 ohmns at 15.5° C. or 59.9° F, 
1 circular mil. is .7854 square mil. 



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Dynamo Troubles 1387 

Correcting Dynamo Troubles. — Inasmuch as the use of 
small direct current electric dynamos is becoming very gen- 
eral^ and since they are frequently in operation under the 
supervision of users who are not as a rule familiar with 
electrical machinery, a few simple pointers relative to the 
care and maintenance of an electric dynamo may help some 
user to avoid considerable annoyance. 

Electrical machinerj^, even though it has been largely 
shrouded in mystery, is, nevertheless, comparatively simple 
apparatus in its operation and maintenance. To a con- 
siderable degree it is a delicate piece of mechanism, by 
which is meant that it cannot be handled with the same 
treatment as one would expect to give a clumsy, crude, or 
inexpensive device. However, there are a few underljdng 
principles which govern such dynamos as are ordinarily 
used in small isolated plants, which, if they are observed, 
will enable practically any operator to maintain and keep 
in perfect running condition any well constructed machine. 
When the dynamo is received from - the factory it should 
be carefully examined to see if it is in apparently good con- 
dition, or whether it shows evidence of having been in- 
jured by rough handling in transit. If this inspection 
points to its having arrived in good condition, its installa- 
tion should be considered in a general way along the lines 
similar to those which would be observed for the installa- 
tion of any piece of machinery. Care should be taken to 
see that the bearings are properly supplied with oil ; that 
the dynamo stands perfectly level on its foundation; that 
the belt is of good quality and free from bumps or improper 
lacing. It may be noted that the dynamo does not neces- 
sarily require an independent foundation, which is de- 
manded by some classes of apparatus. Because of the fact 



1388 Steam Engineering 

that its vibration is very slight^ any rigid or substantial floor 
will answer for this purpose. 

In starting up a dynamo^ only two things which might be 
termed "electricaF^ need be specially considered. The first 
is the direction of rotation, because each dynamo as shipped 
from the factory is so connected as to run in only one di- 
rection and will not generate current if the direction of 
rotation is reversed. It is an easy matter to change the 
connections on a machine so that a reversed direction is 
possible, and a sheet of instructions furnished with the 
dynamo usually covers instructions for this modification, 
but it should be remembered that each dynamo as received 
by the user is so connected as to operate in only one direc- 
tion. 

The second matter for consideration is the speed of the 
dynamo, which should not be less than the speed given on 
the name plate nor greater than ten per cent above the 
speed. A slower speed would interfere with the building 
up of the voltage, while a higher speed would deliver an ex- 
cessive current from the machine. It is needless to add that 
the directions for wiring connections furnished with the 
dynamo should be followed carefully. 

If, after a dynamo has once been running satisfactorily, 
there occurs some difficulty in its operation, the probabilty 
is that, unless the occasion of the trouble is due to some 
mechanical injury or to the dynamo having become sat- 
urated with water or oil, the nature of the trouble will most 
frequently manifest itself in one or two ways. The first 
is that the dynamo will refuse to generate current, and the 
second is that sparking will show itself between the com- 
mutator and the brushes. Under this latter head it is 
worth remembering that the heating of a dynamo is gener- 
ally due to some cause which, if it existed to a greater de- 



Dynamo Troubles 1389 

gree^ would manifest itself in sparking, so that many times 
the heating of the machine means that trouble exists to 
a limited extent, which, if it occurred in a greater degree, 
would manifest itself in sparking. A common exception, 
however, to this statement is that the brushes, if pressing 
too firmly on the commutator, will from their friction pro- 
duce heat. With the above explanation, the more frequent 
difficulties can be classified under the two heads, "Failure of 
the dynamo to generate^^ and "Sparking at the commuta- 
tor.^^ 

If, on starting a dynamo, after its use has been discon- 
tinued for a time, it refuses to generate, which means that 
the operator is unable to secure electricity from it, he 
should first assure himself that the machine is operating at 
its proper speed and that there has been no speed reduc- 
tion, due either to a slowing up of the motive power or to 
a slippage of the belt. If no such difficulty appears, the 
next investigation should determine as to whether or not the 
resistance of the rheostat remains in the field circuit. In 
many instances dynamos can frequently be made to 
generate by simply moving the handle of the rheostat to 
the point marked "highest voltage.^^ The third and possi- 
hly mo^t common cause of failure of a dynamo to generate 
is due to a defective contact between the commutator and 
the brushes. This may be caused by a lack of proper ten- 
sion on the brushes, due either to their being too weak or 
their need of readjustment. Again the brushes and holders 
may have become dirty and gummy, preventing their proper 
action. An excessive amount of grease or dirt on the com- 
mutator occasionally (especially in cold weather) forms a 
scum over its surface which intervenes between it and the 
brushes, retarding the flow of the current. It is possible 
that the obstacle in the path of the current may lie else- 



1390 Steam Engineering 

where than between the brushes and the commutator; as, 
for instance^ loose connection may exist in the wire leading 
from the brushes to the head post. However, the operator 
can look intelligently for the trouble when he realizes that 
the early current generated when the dynamo begins to 
operate is of slight intensity, and obstacles which would not 
interfere with the flow of the current of ordinary propor- 
tions will retard the flow of this initial current, conse- 
(juently a very slight resistance or hindrance may prevent 
the dynamo from generating. 

To these statements may be added the facts that the 
brushes may have become moved from 'their proper position 
or the dynamo may have lost its magnetism. The latter 
condition, however, is rare; and the former will not exist 
unless the machine has been tampered with. In a later 
paragraph is given information relative to the adjustment 
of the brushes. 

This brings us up to the general manifestation of trouble, 
namely, sparking at the commutator, which is probably the 
most frequent difficulty encountered in a dynamo. A 
small red spark, which can be easily recognized as occa- 
sioned by dirt, is not seriously injurious, and a cleaning of 
the commutator and brushes will overcome it. However, a 
vicious, spitting spark will-, in the course of a comparatively 
brief time, materially injure the dynamo, and when first 
detected, steps should be taken to overcome it without de- 
lay. 

Briefly indicating the causes of sparking which do not 
permit of ready classification, it may be possibly occasioned 
by an excessive overload on the machine, due to a leakage in 
the wiring or to the use of too many lights. If this is re- 
sponsible for the sparking,, the machine will heat materially 
in all its parts. It may be true that an open circuit or a 



Dynamo Troubles i391 

break in the wiring of the armature may exist. In this 
instance the spark will be very vicions^ and an examination 
of the commutator will show that it has been burned on 
one of the mica lines across^ its surface. An open circuit 
in one of the fields may also result in sparking^ but this 
can be determined by an unequal heating of the fields. 

Coming, however, to the two most common causes of 
sparking : the first lies in the fact that the contact between 

s 

the commutator and the brushes may not be firm and uni- 
form. The commutator itself may be rough, or the bearing 
surface of the brushes may be irregular; roughness of the 
commutator resulting occasionally by its having been 
burned down or worn. Occasionally the copper wears more 
rapidly than the mica, leaving the mica projecting upon 
the surface of the commutator. If the commutator is 
rough, a piece of No. 2 sandpaper held firmly on its sur- 
face while it is in operation will overcome minor irregulari- 
ties. If this does not correct the trouble, the armature 
should be taken to a first-class machine shop and the com- 
mutator turned off in a lathe. 

If the brushes are so worn that they do not fit snugly on 
the commutator, fasten a strip of No. 2 sandpaper around 
the face of the commutator, the sand side out ; then revolve 
the commutator with this strip of sandpaper attached to it 
until the bearing surface of the brushes will be trued up, 
insuring a perfect contact. Strange as it may seem, the 
most common cause of sparking, occasioned by an improper 
contact, lies in the fact that the user does not recognize that 
carbon brushes wear out and occasionally need to be re- 
placed. Frequently machines are sent back to the manu- 
facturer for repairs when the only occasion of the trouble 
is that the carbon brushes have been worn until they can- 
not rest firmly on the commutator. When the brushes be- 



1392 Steam Engineering 

come so worn that it is difficult with the mechanism of the 
holder to secure a firm pressure against the commutator, 
they should be renewed with new and longer brushes. 

The last occasion for sparking which will be mentioned 
is that the brushes may have been shifted out of their proper 
position in reference to each other and to the commutator. 
On machines which have two-field coils the brushes should 
Test on the commutator at points whjch are exactly opposite 
to each other. On machines which have four-field coils 
these points should be exactly 90° apart. If the brushes are 
properly spaced in reference to each other^ then their cor- 
Tect position on the commutator becomes a matter of locat- 
ing what is known as the ^^neutral point.^^ In order to 
locate this neutral point, move the rocker arm which carries 
all the brushes around with the direction of rotation, while 
the machine is in operation, and carrying a comparatively 
light load. Do this until a slight spark appears, then move 
the rocker arm back in the opposite direction just enough to 
stop the sparking; this will be the neutral point. 

PRACTICAL POINTS. 

Brushes and Commutators. — Brush holders and commu- 
tators will sometimes show excessive temperatures because 
of the heat which may come from a bearing in which the 
armature shaft revolves. The failure of a bearing upon a 
•dynamo or a motor to run cool may be due to any one of 
a great variety of causes, some of which are mechanical and 
others electrical. 

A common cause, and one which is not infrequently over- 
looked is that of lack of sufficient oil in the bearing for the 
purposes of lubrication. When renewing the supply of oil 
to a bearing care should be exercised in the choice of oil. 



Dynamo Troubles 1393 

making certain that it is free from dirt or grit^ and that it 

is an oil of good quality for the purpose in hand. The pas- 

I sages or oil ducts should be carefully examined and kept per- 

\\ f ectly clear for the free running of the lubricant. A bear- 

:ling may be leaking at some pointy causing the oil to run 

> I off much sooner than an attendant would think^ and this 

kind of a defect should be carefully guarded against. 

The modern dynamos and motors have their bearings so 
designed that they are self-oiling^ i, e,, the oil is carried by 
means of chains or rings from the oil chamber beneath the 
bearing proper^ up and over the shaft and through grooves 
provided for the purpose, returning to the well to be used 
over and over again. Gauge glasses are nearly always pro- 
vided by means of which it is possible to observe at any 
and all times the quantity of oil remaining in the well. 
Oil used over and over again in this manner is quite likely 
to gather foreign impurities. It is good practice to remove 
the oil from bearings at least once a month, clean out the 
bearing thoroughly with gasoline, filter carefully the oil 
that is left and return the same to the bearing, adding a 
sufficient quantity of fresh oil to make up for any loss which 
has been the result of operation. 

Gritty substances are very likely to work into bearings at 
different times, depending upon the use which is made 'of a 
motor or a generator. If electrical apparatus is to be placed 
in a space that is dirty, and cannot well be kept clean, then 
it is a good precaution to have the machine suitably en- 
closed, or else to have the bearings completely enclosed with 
tight-fitting plates about the shaft so as to exclude foreign 
substances. Whenever it is found necessary to wash out a 
bearing in order to remove any dirt, care should be exer- 
cised not to get any water or kerosene upon the commutator 
or windings of the machine. 



1394 Steam Engineering 

A roughened shaft or a tight fit between tlie shaft and ' 
the sleeve of the bearing may cause lieating. These diffi- 
culties are purely mechanical and are easily remedied, once 
that the source of the trouble is ascertained. 

Sudden and excessive strains sometimes spring the shaft 
of a generator or a motor, and it not infrequently happens 
that with some types of bearings they are thrown out of 
line. Either of these causes will bring about a heating of 
the bearing. A bent or crooked shaft can rarely ever be 
straightened, the only remedy being a new one. Bearings 
that can be thrown out of line for the reasons mentioned 
are also susceptible of being properly aligned by means of 
the caps and screws for holding them in position. 

The end thrust of a collar on the armature shaft, upon 
one side or the other of the machine, may cause a heated 
bearing. When machines are driven by belting, or when 
motors are connected with shafting by belting, it is an easy 
matter to ascertain whether the armature is running freely 
with respect to the belt connection. A stick placed against 
the end of the shaft would enable one to move the armature 
back and forth with very little effort. In fact, every arma- 
ture should have free end play, and if a test with a stick as 
mentioned does not show that such a free end play does 
exist, then the machine should be lined up with respect 
to its belt, so that such end play is secured. 

The bearings may wear down sufficiently in time to per- 
mit of the armature bands rubbing against the pole pieces, 
or stationary iron of the machine. This can often be de- 
tected by placing the ear near the frame of the machine 
opposite the pole piece where it is thought that the arma- 
ture might come in contact. It might also be detected by 
turning the armature over. slowly with the belt removed and 
with the field current turned on. It "might also happen. 



Dynamo Troubles 1395 

however^ that the. armature will not touch any of the field 
poles^ except when running under load with the belt on. 

3 The positive evidence of rubbing lies in an examination of 
the circumference of the armature itself when the bands 

[ around the armature will show whether there has been any 
rubbing or not. This kind of an examination can usually 
be made without removing the armature from the machine. 
If there should be positive evidences of rubbings it must 
not be allowed to continue. 

The pulley, the belt or other parts of the revolving arma- 
ture shaft may rub. against adjacent surfaces, and bring 
about a scraping or a rattling noise. The movement of the 
shaft back and forth in its bearings in one direction or an- 
other may stop the noise, in which case it will be a simple 
matter to locate the cause, after which it will be an equally 
-simple matter to remedy the trouble. 

Generally, in starting up a new generator or motor, the 
new and unused carbon brushes upon a new, and previously 
unused commutator will cause an unpleasant squeaking or 
a hissing. The sound is usually of a high pitch and is easily 
located. Sometimes, it may be due to but one or two new 
brushes. These can be located by removing one brush at a 
time until the noisy ones are found. Then by moistening 
them slightly with a light oil, the noise from that particular 
brush will be stopped. There should not, however, be so 
much oil used for this purpose so that any of it will adhere 
to the brush in the form of drops. It sometimes happens 
that the commutator has not been finished off as 
smoothly as it should have been and this, of course, 
would cause a considerable humming until the commutator 
surface had been worn over sufficiently to take on a polished 
appearance. If the commutator is rough enough to cause a 
hissing of the brushes, it should be polished off by hand be- 



1396 Steam Engineering 

fore it is put into operation. This can be done in the 
manner already described^ and would insure a much bet- 
ter commutator in service than if allowed to run along in 
the rough state^ trusting to luck that it will assume a pol- 
ished appearance as a result of operating conditions alone. 

A squeak due to the slipping of a belt upon the pulley 
is easily located^ and not confounded with any other noise 
which may result from operating any class of machinery. 
Whenever such slipping of a belt occurs^ it means a loss 
of power^ and that means expensive operation. A care for 
the details of operating costs will not permit of a squeaking 
belt at any point. 

Another kind of humming is often present in motors and 
in some kinds of generators. This is the humming which 
is something of a musical sounds and is likely to be con- 
fined to the armature teeth as they pass the pole faces at 
high speed. It is a molecular vibration due to the magnetic 
reversals in the iron. If it is an objectionable feature in 
the operation^ it may be remedied by trimming off the ends 
of the pole faces so that the full length of an armature tooth 
would not be likely to leave the pole face throughout its 
entire length at the same instant of time^ but would shade 
off instead. The testing of generators and motors in the 
shops of the builders^ however^ is supposed to reveal exces- 
sive humming, and the trimming of pole faces should be 
done before the machine is sent to the shipping room. In 
general, it is always well to be certain that the noises of 
operation come from the electrical apparatus, and not from 
some other equipment which might be close by. 

Transformer Oil. — Transformer oil, its proper character, 
treatment and use, has been much neglected by central sta- 
tion engineers. It forms one of the weak links in the chain 
of a high-tension electric-transmission system. In its dual 



Transformer Oil 1397 

function as insulator and cooler, it requires high dielectric 
strength, and high flash point, combined with great fluidity. 
It should be neutral so as to not dissolve the insulation of 
the core and coils immersed in it. 

Of these qualities, the dielectric strength is the most va- 
riable, for it depends largely upon the amount of moisture 
present. The popular axiom that oil and water do not mix 
is not scientifically correct, for oil does absorb a small 
amount of moisture that materially lessens its dielectric 
strength. Instances have been known of transformer oil 
having broken down under 16,000 volts when wet, but 
which stood the test of 40,000 volts after being dried. 

While oil and water do not chemically mix, they may 
mingle so closely as to require steam, or rheostat heating to 
remove the water. Every precaution should be taken to 
keep oil dry during shipment and in use, for it abhors dehy- 
dration even more than nature abhors a vacuum. 

It should have a high fire or flash test to eliminate dan- 
ger of fire. Crude oil is refined by frictional distillation, 
the most volatile products passing off first. These are low 
in gravity and in burning temperature, as is exemplified by 
gasoline. Kerosene for use in lamps is one of the next 
products, soon followed by an oil suitable for transformer 
purposes. This usually has a gravity of 30° Baume or 
less, and burns at about 300° Fahrenheit. The higher the 
temperature at which the product is distilled, the greater is 
its viscosity. Consequently, what is gained in flashing tem- 
perature is lost in fluidity. Acid introduced into the refin- 
ing must be removed by adding just enough alkali to ren- 
der the oil neutral. Disastrous fires have been known to 
result from the volatilization of the oil by an arc. 

Another frequent trouble is the deposition of a thick, 
carbonaceous, jelly-like sludge on the cooling coils, and in 



1398 Steam Engineering 

the circulating ducts. The former are covered so thick that 
cooling is not effected^ and the latter are so clogged that, 
circulation is difficult. Such deterioration generally occurs 
when the oil has been overheated. The deposit is easily 
washed off when hot^ but becomes hard and brittle upon 
exposure to the air^ resembling bitumen in this respect. The 
deposits around the points of high potential allow creepage, 
so that a medium of high resistance may become a con- 
ductor. 

But careful examinations of these troubles show that 
they are usually due to no inherent fault of the oil, but 
to the transformer design, or more particularly to the at- 
tendant's carelessness. 



6666666666 




6666666666 



Fig. 661 

Careful breakdown tests should be made not only when 
the oil is furnished, but at frequent intervals thereafter, 
once a month not being too often for main stations. Tests 
for acidity will avoid the destruction of the insulation by dis- 
solving, and flash tests will often prevent fires. The carbon 
may be removed by occasional filtering. In case of leaky 
cooling coils, the water should be drawn off from the bot- 
tom until such time as the transformer can be taken out of 
service and properly repaired. 

All this trouble occurs with both water, and self-cooling 
transformers. Where water is plentiful, it has been sug- 
gested that outside circulation of the oil would cause bet- 
ter cooling, and larger ventilating ducts would not become 



j^ Transformer Oil 1399 

clogged. We attain success only by the most careful at- 
tention to the details of our work. Look after the oil^ and 
transformer troubles will take care of themselves. 

Three Wire System with One Dynamo, — When the load 
on one side of the middle or neutral wire exactly equals the 
load on the other side^ as in Pig. 661^ the circuit is bal- 
anced^ but it is very seldom that such load conditions exists 
at least for any length of time, and when there is a differ- 
ence between the loads carried by the two sides, the circuit 
is unbalanced. 

In order therefore to successfully operate a three wire 
system with one dynamo, it becomes necessary to provide 
some method of taking care of the surplus current on the 




4 Amperes -i-/*" 5 Ampere? 



1 Ampere .=. 



V 



'4 Amperes^ "]" ^ ■^"'' 



2HI 



rru Th 



t 



Fig. 662 



lightly loaded side, and transferring it to the heavily loaded 
side ; in other words, to balance the circuit. There are two 
methods by which this may be accomplished. 

The first and most simple method of compensating for 
unbalancing is to connect a storage battery between the 
two main wires, and then connect the neutral wire to the 
middle point of the battery, as shown in Fig. 662. Here 
are shown connected 10 lamps on one side, and 6 on the 
other. The direction of flow of the current is indicated 
by the arrows. Assuming that the resistance of each lamp 
is 220 ohms, which is the ordinary value for 110 volt lamps, 
the joint resistance of the group of 10 lamps would be 



I 



1400 Steam Engineering 

220^10=22 ohms. The joint resistance of the 6 lamps 
on the other side would be 220-^6=36.66 ohms. 

The total resistance of both groups of lamps would be 
22+36.66=58.66 ohms^ and the volume of current flowing 
through both groups would be 220-^58.66=3.75 amperes. 
Assuming that each lamp requires % ampere of current/ 
the group of 10 will require 5 amperes, and the group of 
6 requires 3 amperes. As the volume of current equals 3.75 
amperes, it is evident that the 10 lamps will not get enougli' 
current, while the group of 6 will get too much^ unless, as ' 
before mentioned, a balancer be provided, and right here 
is where the storage battery enacts its role. Under the con- ■ 
ditions shown in Fig. 662, the A half of the battery will 
deliver just enough current, provided the voltages are suit- 
ably proportioned, to supply one-half of the excess or un- 
balanced load on the heavy side of the system. The dynamo 
supplies the other half of the excess current which comes in 
on the neutral wire, with the current supplied by the A 
section of the storage battery, and returns to the dynamo 
through the B half of the battery charging that section. 

This proportion holds good for any degree of unbalanc- 
ing; that is, that part of the battery on the heavily loaded 
side will send out one-half of the current in the neutral 
wire, and the other half will go through the part of the bat- 
tery that is on the light load side of the neutral. 

This arrangement, though apparently ideal in simplicity 
on paper, is not so attractive in practice, for the reason that 
a regulator is needed in conjunction with the battery in 
order to prevent it from exhausting itself when the load is 
heavy, or drawing too heavily from the line when it i& 
light. Moreover, the two halves of the battery cannot be 
kept in equal condition, because one side would do more 
work than the other, unless the circuit could be unbalanced 



Three Wire System — One Dynamo 140i 

alternately, and equally on, first one side and then the other. 
This difficulty can be met, however, by exchanging the two 
sections at regular intervals, say once a week. 

A more practical method of compensation is by means 
of what is commonly termed a ^^otor-balancer,^^ but is 
more correctly a motor-compensator. This consists of two 
small motors exactly alike in all respects, their shafts rigidly 
coupled together and their armatures connected, one on 
each side of the neutral wire, as indicated in Fig. 663, where 
120 lamps are represented on each side of the neutral wire. 
Here it is assumed that the motor armatures require one 
ampere to drive them, or 220 watts (110 watts each), and 
for simplicity the current required by their field windings 
is ignored. So long as the load is balanced, the two arma- 
tures will take current from the main wires only, and will 
revolve idly. If more load is added to one side, however, 
or some load taken off the other side, the equilibrium be- 
tween the voltages of the two sides will be upset ; the volt- 
age at the brushes of the motor on the lightly loaded side 
will be higher than that at the brushes of its mate, and it 
will drive the latter at a speed beyond that due to the cir- 
cuit voltage, making a dynamo of it, and forcing it to carry 
the unbalanced part of the heavier load on the circuit. This 
is illustrated in Fig. 664, where 120 lamps are shown on one 
side and 60 on the other, each of the circles representing 10 
lamps, taking I/2 ampere each. What causes the distri- 
bution of current shown is this: When the load in the B 
division is reduced the voltage rises, because the losses in 
the dynamo and circuit wires are reduced; the voltage be- 
tween the neutral and the negative wires rises more than 
that between the positive and neutral, because the resist- 
ance there is higher — all tlie reduction of load has occurred 
in that division of the circuit. The armature B, therefore, 



1402 



Steam Engineering 




\smmu — <£mmiJ 








jojcsnadtuoo 







J 



Three Wire System — One Dynamo 1403 

speeds up^ dragging tlie armature A with it until the volt- 
age of the latter increases above that of its side of the cir- 
cuit sufficiently to carry half of the excess load on that side, 
minus the power required to drive the two machines. This 
power was assumed to be 220 watts; the current taken by 
the two armatures in series in Fig. 663 being one ampere 
and the total voltage 220. Here, one of the armatures does 
all the work, so that the whole 220 watts must be applied 
to it, in addition to an amount of power equal to that being 
delivered by the armature A working as a dynamo. As the 
armature B takes its current now from the unbalanced cur- 
rent coming in on the neutral wire, it works at 110 volts 
and therefore requires 2 amperes to overcome the losses in 
the two machines (the losses in the windings are ignored 
to simplify the problem) ; the neutral wire must carry 30 
amperes because the 60 lamps in the negative division will 
pass only 30 amperes. Deducting the 2 amperes for motor 
losses leaves 28 amperes, which divides between the two 
machines, 14 amperes supplying the motor with the energy 
necessary to produce 14 amperes from the armature now 
driven as a dynamo. 

Another way to arrive at the division of current is as 
follows : The main dynamo must supply all of the energy 
represented in the circuit; all that the compensator does is 
to transfer the surplus energy from one side of the circuit 
to the other — it cannot supply any additional energy be- 
cause it is driven by energy taken from the main circuit. 
Now the lamps take each V2 ampere at 110 volts, or 55 
watts; there are 180 lamps, requiring 180X55=9900 watts. 
The compensator requires 220 watts to overcome its no- 
load losses, the extra losses at load being ignored for the 
present. The lamps and compensator together, therefore, 
require 9900-|-220=10,120 watts. Ignoring line losses. 



1404 



Steam Engineering 



the generator works at 220 volts^ and in order to deliver 
10,120 watts it must deliver 10,120^220=46 amperes. 
Since the lamps in the positive division (A) require 60 am- 
peres, the armature A working as a dynamo must supply 
60 — 46=14 amperes. Consequently, of the 30 amperes 
in the neutral wire, 14 must have been generated in the 
little machine; the other 16 pass through the motor arma- 
ture B to the main dynamo, as prevously explained. 




Fig. 665 



The exact figures in practice would not be those here 
stated because the line losses, the current in the field wind- 
ings of the compensator, and the losses in their armature 
windings affect the current distribution. The principle, 
of course, is not affected ; the machine on the lightly loaded 
side of the system always runs as a motor, and drives its 
mate as a dynamo, the latter supplying about one-half of the 
difference between the two divisions of the load, minus the 
power required to drive the machine. The losses do affect 



Three Wire System — One Dynamo 1405 

the voltage regulation^ however. If the armature windings 
of the compensator are of very low resistance^ the voltages 
on each side of the neutral will be kept almost exactly 
equal; if the armature resistances are high^ the voltage be- 
tween the neutral and the main wire which carries the 
heavier load will be appreciably lower than that on the 
other side of the system. 

The regulation obtained with motor compensators can be 
much improved by cross-connecting the field windings^ as 
shown in Fig. 665. The result of this is that when the 
load on the side A^ for example, is less than that on the 
other side, the voltage of the side A being higher than 
that of the side B, the field strength of the machine A 
will be weaker than that of the machine B, and its 
speed will be higher than it would be with a steady 
field. The m^achine B, on the other hand driven 
as a dynamo, will have its field strengthened, and 
will deliver a higher voltage than it would otherwise. In 
other words the machine that runs as a motor runs at a 
higher speed, thus giving its mate a higher voltage, and the 
latter will also have a stronger field, increasing its voltage 
still more, with the connections as shown, in Fig. 665, than, 
with the arrangement shown in Figs. 663 and 664. The 
armature capacity of a motor balancer in amperes, must be 
equal to one-half of the current that will flow in the neutral 
wire when the system is out of balance by the maximum 
amount possible under operating conditions, plus the cur- 
rent required to overcome all losses in the two armatures 
at full load. The losses in small armatures range from 
5 to 10 per cent at full load ; therefore if the armatures of 
the balancer can carry 55 per cent of the maximum cur- 
rent that is likely to ever flow through the neutral wire 
they will be large enough. 



1406 



Steam Engineering 



ARC LAMPS. 

When two rods of carbon are connected to a source of 
current^ and their ends brought into contact with each other, 
and then separated a slight distance, the current will con- 
tinue to pass across the interval, but an intense heat is 
generated, and the space between the ends of the carbon 
rods is filled with carbon Vapor, and minute particles. The 
current passes over this space in a bow-shape path or arc. 




Fig. 666 

and it is from this fact that the lamp gets its name. The 
arc is constantly moving, and generally revolves around 
the carbon points. This can be easily seen by looking closely 
at a burning lamp through a smoked glass. After a lamp 
has been burning for some time on direct current the car- 
bons assume the shape shown in Fig. ^Q^, the upper or 
positive carbon assuming a cup shape, while the lower car- 
bon generally burns to a point. This cup shape formation 



Arc Lamps 



1407 



on the upper or positive carbon acts as a reflector to throw 
the light downward. The positive carbon burns away 
about twice as fast as the negative carbon^ and lamps must 
be trimmed accordingly. Sometimes the current feeding 
arc lamps (on direct current systems) becomes reversed^ 
either through the dynamo reversing its polarity or through 




CUT-OUT 

STARTING 
RESISTANCE 



Fig. 667 
diagram of constant-current series arc lamp mechanism. 

wrong plugging of the switchboard. The lamps will now 
burn ^^upside down/^ or^ in other words^ the bottom carbon 
will be the positive one. In such a case, if let go, the 
carbon holders of the lamp will be burned and the lamp 
will burn for only half the time for which it was intended, 
owing to the fact that the lower or negative carbon is only 



1408 Steam Engineering 

one-half as long as the upper or positive carbon. Such a 
condition can be determined by either of the following 
ways: See if the light is being thrown downwards. See 
which carbon is burning away the faster. Eaise the car- 
bons and notice the formation of the carbon tips. When 
the carbons are separated it will be noticed that the tip of 
one carbon is considerably hotter than the other, and is 
heated a longer distance from the point ; this is the positive 
carbon. 

The heat of the arc is very intense, that of the positive 
pole being 7200° Fahr. and the negative 5400° Fahr. Fig. 
667 illustrates the action of a constant current or series are 
lamp. It shows the lamp inactive, the carbons in contact, 
and the cut-out closed. If current is turned on, it goes 
through the cut-out. In series with the cut-out is a coil 
which provides the starting resistance. Its resistance shunts 
sufficient current through the series magnet to cause it to 
attract its armature and raise the clutch. This separates 
the carbons, the arc strikes, and the current is shunted 
through the shunt magnet. This at once begins to regu- 
late the length of the arc. 

The armatures of the shunt and series magnets operate 
a rocker arm which is pivoted between the magnets, so that 
the series and shunt magnet have reverse effects on the 
movable upper carbon. As the shunt-magnet armature is 
drawn up, the clutch descends, owing to the action of the 
rocker arms, and the reverse action takes place when the 
shunt-magnet armature descends. In this way the increase 
of arc length, shunting more current through the shunt 
magnet, causes the clutch to descend and the arc shortens. 
The dash-pot is shown to the left of the central tube above 
the rocker arm. Immediately below the clutch is the trip- 
ping platform, seen extending over the top of the globe. 



Arc Lamps 140& 

Adjusting Weight. — This slides back and forth upon the 
rocker arm attached to the two armature rods. This is 
fastened in any desired position by a setscrew. For varia- 
tions in current exceeding 0.2 ampere above or below the 
rated current of the lamp^ the weight must be shifted. By 
moving the weight toward the clutch rod the voltage is 
reduced^ and moving at away from the clutch rod increases 
the voltage. 

Fig. 668 shows a diagram of connections for the improved 
Brush arc lamp. These lamps are used on constant current^ 
or series systems^ and their action is as follows : 

The carbons should rest in contact when the lamp is cut 
out. When the switch is opened^, part of the current from 
the positive terminal hook P goes through the adjuster to 
the yoke^ and thence through the carbon rod and carbons 
to the negative terminal hook N. The remainder of the cur- 
rent goes to the cut-out blocks but^ as the cut-out block is 
closed at first, the current crosses over through the cut-out 
bar to the starting resistance, and so to the negative side of 
the lamp. A part of it, however, is shunted at the cut-out 
block through the coarse wire of the magnets, and so to the 
upper carbon rod and carbons and out. This shunted cur- 
rent energizes the magnet, and so raises the armature which 
opens the cut-out, and at the same time establishes the arc 
by separating the carbons. 

The fine wire winding is connected in the opposite direc- 
tion from the coarse wire winding, and its attraction is 
therefore opposite. When the arc increases in length, its 
resistance increases, and consequently the current in the 
fine wire is increased. The attraction of the coarse wire 
winding is therefore partly overcome, and the armature 
begins to fall. As it falls, the arc is shortened and the 
current in the fine wire decreases. The mechanism feeds 



1410 



Steam Engineering 



r\, 




Fig. 668 



the carbons, and regulates the arc so gradually that a perfect, 
steady arc is maintained. 

The fine wire of the magnets is connected in series with 



I 



Arc Lamps 1411 



e winding of a small auxiliary cut-ont magnet at the top 
of the mechanism. 

This magnet^ which also has a supplementary coarse 
windings does not raise its armature unless the voltage at 
the arc increases to 70 volts. The two windings connect 
at the inside terminal on the lower side of the auxiliary cut- 
out magnet^ and the current from the fine wire of the main 
magnets passes through both windings and then to the cut- 
but blocks and so to the starting resistance and out. 

If the main current through the carbon is interrupted 
(as by breaking of the carbons) the whole current of the 
lamp passes through the fine wire circuit. Before this 
excessive current has time to overheat the fine wire circuity, 
it energizes the auxiliary cut-out magnet^ and closes a cir- 
cuit directly across the lamp through the coarse wire on 
the auxiliary cut-out to the main cut-out block^ and thence 
to the negative terminal. 

The auxiliary cut-out operates instantly^ and prevents 
any danger to the magnets during the short period required 
for the main armature to drop and throw in the main cut- 
out. When the main cut-out operates^ the armature of the 
auxiliary cut-out falls, because there is not sufficient cur- 
rent in that circuit to energize the magnet. 

The voltage at which the auxiliary cut-out magnet oper- 
ates depends on the position of its armature, which is reg- 
ulated by the screw securing the armature in position. It 
should be adjusted to operate at not less than 70 volts. 

One of the three methods of suspension may be used for 
Brjish lamps. If chimney suspension, which is the most 
coijimon, is adopted, the wire, cable or rope used to sus- 
peiid the lamp must be carefully insulated from the chim- 
ney. For this purpose a porcelain insulator should be in- 



1412 



Steam Engineering 



sorted between the support and the lamp, as shown m 
Fig. 669. 

Hook suspension may be used to advantage in some 
places, but great care must be taken to insulate the support- 



■ 1 

j j 


1 




' : 1 


m 








I 


f 






. 


i 


I, 






B 


MK 




m 


Bk 




i 


% 


j 



Fig. 669 

ing wires from any conductors, as the hooks form the ter- 
minals of the lamps. 

The most convenient arrangement for indoor use is to 
suspend the lamp from a- hanger board. The porcelain 
base of the hanger board prevents short circuits or grounds. 



Arc Lamps 1413 

A protecting hood is not necessary for outdoor use;, as 
the lamp chimney and its base are one casting and effect- 
ually exclude rain or snow. > 

The lamps run on circuits of ^.^ amperes for 1^200 and 
9.6 amperes for 2,000 nominal candlepower. In case it is 
necessary to run a lamp on a circuit differing from the 
standard, the lamp may be adjusted by moving the contact 
on the adjuster. About one ampere either above, or below 
the normal may be compensated for by this means. 

Permanent adjustment for special circuits of variation 
greater than one ampere is made by filing the soft iron arma- 
ture. The clutch should be so adjusted that the center of 
the armature is -Jf in. above the plate when the trip on the 
first rod is touching the bushing, and \^ in. when the trip 
on the second rod is in a similar position. A small gauge 
is convenient for adjusting the clutch. The position of the 
trip of the clutch determines the feeding point of the lamp. 

After thoroughly repairing and cleaning the lamp, it 
should be run a short time before installing. Lamps should 
not be tested in an exposed place, as a strong draft of air 
will cause unpleasant hissing which may be mistaken for 
some internal trouble. 

Lamps should not hiss or flame if good carbons are used. 
A voltmeter should always be used when adjusting or 
testing. 

The lamp terminals are marked P (positive) and N 
(negative) and should be connected into circuit accord- 
ingly. 

[The carbons should be solid and of uniform quality. For 
tl^e best results, the upper carbon should be 12 in.XiV ^^-^ 
and the lower 7 in.XiV i^- The stub of the upper carbon 
mjay then be used in the lower holder when retrimming. 



1414 Steam Engineering 




At each trimming the rod should be carefully wiped with 1 


clean cotton waste. If 


any sticky or dirty spots appear, 


. 






*J 


•^■B ^W-^: 




--^^^ 


wtn'MiMBr ^^^8*. 




^ 


^^^^~ ?^P^E^ ^p^s-^^— 




M 


B^B^ t>»BB| L^ 1^ 




- '^y 


nil wl 




M 


^w 




ii^^S 


■flMpii. 




IhR 


^^^^B^^^^^^^^^^^^B 




fllHUb^l&i 


^^^^^^^^^m^HB 





Fig. 670 



which cannot be readily removed with waste, use a piece 
of well-worn crocus cloth/ always being careful to use a 
piece of clean waste before pushing the rod into the lanp. 



Arc Lamps 1415 

It should never be pushed up into the lamp in a dirty con- 
dition. 

The carbon rod may be unscrewed and removed with a 
small screw driver, or small strip of metal inserted in the 
slot cut in the rod cap. The cap will remain in the hole 
through the yoke when the rod is taken out. 

In Fig. 670 an interior view of the Thomson-Houston 
arc lamp is shown. This lamp is also used on constant 
current systems. 

The lamps should be hung from the hanger boards pro- 
vided with each lamp, or from suitable supports of wire or 
chain. 

As the hooks on the lamp form also its terminals, they 
should be insulated, where a hanger board is not used, from 
the chains or wires used to support the lamp. 

When the lamps are hung where they are exposed to the 
weather, they should be covered with a metal hood, to pre- 
vent injury from rain and snow. 

In such cases, care should be taken that the circuit wires 
do not form a contact on the metal hood and short circuit 
the lamp. 

Before the lamps are hung up they should be carefully 
examined to see that the joints are free to move, and that 
all connections are perfect. 

No lamp should be allowed to remain in circuit, with the 
covers removed and the mechanism exposed. Such practice 
is dangerous, and in violation of insurance rules. 

The object of testing the lamps in the station is to find 
any defects, if such exist, and to test all the conditions of 
:i[unning, before delivering them to customers. The lamps 
dhould not be hung up in their respective places in the ex- 
ternal circuit, until everything is running with perfect 
satisfaction. 



1416 



Steam Engineering 



The tension of the clamp which holds the rod is adjusted 
"by raising or lowering the arm at the top of the guide rod. 
(Sec Fig. 671.) If the tension is too great the rod and 
clutch will wear badly, and the feeling will be uneven, 



i^ 




Fig. 671 



causing unsteadiness in the lights. Too little tension will 
not allow the clutch to hold up the rod, and any sudden 
jar to the lamp will cause the rod to fall and the light to go 
out. 



Arc Lamps 1417 

The double carbon, or M lamp, should have the tension 
of the second carbon a trifle lighter than the first one. 

When adjusting the tension, be sure to keep the guide rod 
perpendicular and in perfect line with the carbon rod; it 
should be free to move up and down without sticking. 

The tension of the clutch in the D lamp should be the 
same as that of the K lamp. It is adjusted by tightening 
or loosening the small coil spring from the arm of the 
clutch to the bottom of the clamp stop. 

To adjust the feeding point in the K lamp, press down 
the main armature as far as it will go, then push up the 
rod about one-half its length, let go the armature and then 
press it down slowly and note the distance of the bottom 
side of the armature above the base of the curved part of the 
pole. When the rod just feeds, this distance should be % in. 
If it is not, raise or lower the small stop which slides on the 
guide rod passing through the arm of the clutch, until the 
carbon rod will feed when the armature is 1/4 iii- from the 
rocker frame at base of pole. 

To adjust the feeding point of the M lamp, adjust the 
first rod as in the K lamp. Then let the first rod down 
until the cap at the top rests on the transfer lever. The 
second rod should feed with the armature at a point iV i^- 
higher than it was while feeding the first rod, that is, it 
should be -{^ in. from rocker frame at base of pole. 

The feeding point of the D lamp is adjusted by sliding 
the clamp stop up or down, so that the rod will feed when 
the relative distances of the armatures of the lifting magnet, 
and the armature of the shunt magnet from rocker arm 
frame arc in the ratio of 1 to 2. There should be a slight 
lateral play in the rocker, between the lugs of the rocker 
frame. 



1418 Steam Engineering 

The armatures of all the magnets should be central with 
cores^ and come down squarely and evenly. There should 
be a separation of 3^ in. between the silver contact points^ 
when the armature of the starting magnet is down. This 
contact should be perfect when the armature is up. The 
arm for adjusting the tension should not touch the wire or 
frame of the lamp when at the highest point. There should 
be a space of ^'V in. or % in. between the body of the clutch 
and the arm of the clutch^ to allow for wear on the bearing 
surfaces. 

Always trim the lamp with carbons of proper length to 
cut out automatically^ that is^ have twice as much carbon 
projecting from the top as from the bottom holder. Al- 
ways allow a space of % in.^ when the lamp is trimmed, 
from the round head screw in the rod, near the carbon 
holder, to the edge of the upper bushing, so that there will 
be sufficient space to start the arc. 

The arcs of the 1,200 candlepower lamps should be ad- 
justed to 3/64 in., with full length of carbon. Arcs of 2,000 
candlepower lamps should be adjusted from -^q to 3^2 in. 
when good carbons are used. 

The action of a lamp that feeds badly may often be con- 
founded with a badly flaming carbon. The distinction can 
readily be made after a short observation. The arc of a 
lamp that feeds badly will gradually grow long until it 
flames, the clutch will let go suddenly, the upper carbon 
will fall until it touches the lower carbon, and then pick 
up. A bad carbon may burn nicely and feed evenly until a 
bad spot in the carbon is reached, when the arc will sud- 
denly become long and flame and smoke, due to impurities 
in the carbon. Instead of dropping, as in the former case, 
the upper carbon will feed to its correct position without 
touching the lower carbon. 



Arc Lamps 



1419 



In a series arc lamp the shunt coil is used to regulate the 
voltage over the arc. With constant potential arc lamps 
this shunt coil is not needed^ owing to the fact that the 
voltage over the lamp is practically constant. Fig. 672 
shows a diagram of an arc lamp for use on constant poten- 
tial circuits. The upper carbon is supported by means of 
an iron yoke which forms a core to the two solenoids M M. 
Current entering binding posts T passes through the wind- 
ings of these two solenoids and then through the carbons 




Fig. 672 

and through the resistance coil E to the other terminal of 
the lamp. The action of the lamp is as follows : Current 
passing over the solenoids M M is regulated by the resist- 
ance across the arc. This current produces an electromag- 
netip pull on the iron core and floats^ magnetically^ the core 
and upper carbon. When the carbons burn away at the 
crater the distance from point to point of the carbons is 
incieased^ and a corresponding increase in resistance to the 
flow of the current takes place. This reduces the flow of 



1420 Steam Engineering 

current around the solenoids and correspondingly reduces 
the electromagnetic pull on the core ; the iron core and car- 
bon fall a slight distance by gravity. In so doing the dis- 
tance at the crater is decreased and the flow of current 
increased^ and a corresponding increase in resistance to the 
solenoids and drawing up the core and carbons. In this 
way a very nice equilibrium between gravity and magnetic 
pull is maintained. It will be noticed that this lamp has 
no automatic cut-out as has the constant current arc lamp. 
In a series arc lamp when the carbons are all consumed, the 
automatic cut-out closes the circuit from the positive and 
negative binding posts of the individual arc lamp, thereby 
maintaining a path through the arc lamp over which the 
current can continue to flow to supply the remaining arc 
lamps in the series circuit. 

The series arc, as its name would indicate, is the most 
simple of all lighting circuits. The lamps are arranged so 
that all the current from the positive pole of the dynamo 
goes through each, and from the last on the conductor 
leads back to the dynamo. The series system is more gen- 
erally used where it is desired to illuminate a large district, 
as in street lighting. It is also used to some extent in store 
lighting, although the series arc is fast being replaced with 
the constant potential arc for this purpose. 

In the low tension or constant potential arc lamp the 
use of a cut-out mechanism is not necessary, because these 
lamps bum singly across the system of wiring, where a con- 
stant potential is maintained, and hence when the carbons 
are all consumed, current simply ceases to flow across them. 
In the open arc lamp the potential across the crater is 
usually from 45 to 50 volts, while in the inclosed arc lamp 
the potential across the crater is from 68 to 75 volts. This 
is due to the increased resistance through the crater, because 



Arc Lamps 1421 

of the peculiar nature of the gases emitted from the crater 
burning in a condition with practically no atmosphere. 
"When such an arc lamp is connected across a 110 volt cir- 
cuit, the lamp contains a resistance coil in the mechanism 
box over which the current must flow before producing the 




Fig. 673 

arc, see E. Fig. 673. This resistance coil assists to reduce 
the pressure from 110 volts to the pressure required by the 
arc or crater. If, for instance, the electromotive force across 
the wires supplying current to a low tension arc lamp is 
110 volts, and the pressure required to maintain the arc or 



1422 Steam Engineering 

crater is 70 volts^ then the resistance coil chokes down the 
electromotive force from 110 to 70^, or 40 volts. If the arc 
consumes 4 amperes of current then the loss is 4 (amperes) 
times 40 (volts)^ or 160 watts. This 160 watts is lost by 
heat radiating to the atmosphere frem the wire of the resist- 
ance coil. The constant potential lamp is usually referred 
to as the low tension arc lamp. The high tension arc lamp 
generally burns with the arc in the open air, while the low 
tension lamp burns with the arc encased in a small glass 
bulb so arranged as to permit the upper carbon to slide into 
the bulb in a manner that will maintain, as near as possible, 
a condition whereby the arc burns in a gas containing no 
oxygen. The enclosed arc lamp has the advantage of burn- 
ing a considerable number of hours without being recar- 
boned or trimmed ; but it also has the disadvantage that the 
bulb enclosing the arc turns black after burning for some 
time, caused by the gases emitted from the arc. This ren- 
ders the bulb partially opaque, consequently imprisoning a 
considerable quantity of useful light. Enclosed arc lamps 
are also operated in series systems, and where they are so 
used the objection of loss due to the cutting down of the 
voltage (as in constant potential lamps) is overcome. En- 
closed lamps are also operated on alternating current sys- 
tems. 

The operation of the alternating current arc lamp, and 
the mechanism in the lamp is very similar to that of the di- 
rect current arc lamp, but the magnets instead of being con- 
structed of solid iron are laminated in a manner similar to 
the system of lamination explained in the construction of 
armatures. These laminated cores, and other parts forming 
the magnetic circuit in the arc lamp are necessary to avoid 
eddy currlents. The crater has neither a cup shape on the * 
upper carbon, nor a point on the lower carbon, because cur- 



Arc Lamps 



1423 



rent flows through the crater alternately positive^ and nega- 
tive with each alternation. In the alternating arc lamp the 
upper and lower carbons burn away with almost equal 
rapidity^ and the same quantity of light is projected upward 
as downward. 






Fig. 674 



Fig. 675 



Fig. 676 



In Pig. 673 is shown an arc lamp with the case removed. 
The two upper coils are the coarsely wound series coils, 
while the two lower coils are the finely wound shunt coils. 
This lamp is adapted for an enclosed arc bulb. The mag- 
netically attracted cores are U shaped^ and both cores are 
connected together mechanically by non-magnetic metal. 



' 



1424 ' Steam Engineering 

such as brass or zinc^ so that the magnetism set up in the 
shunt coils will not be affected by the magnetism set up by 
the series coils. This scheme is used in alternating current 
lamps, while in direct current lamps the cores are made of 
H shaped iron not laminated. 

In Figs. 674 to 676 are shown three views of series en- 
<3losed, alternating current arc lamps of the Western Elec- 
tric Company. 

Fig. 674. Side view of lamp, showing one series and one 
shunt spool, lever movement and adjusting weight. This 
weight is fastened upon a threaded rod, and the finest ad- 
justment can be obtained by screwing the weight backward 
or forward. Threads can be clamped in position when the 
•correct adjustment is obtained. 

Fig. 675. Front view of lamp, showing shunt spools, 
supporting resistance and cut-out. Note that lever carries 
no current when in normal working position, but that in- 
sulated bridge forms connection across two contacts, com- 
pleting cut-out circuit when in position shown in cut. 

Fig. 676. Eear view of lamp, showing series spool, short 
circuiting switch, and manner of suspending dash-pot. Note 
that the dash-pot is inverted, allowing such dirt as may 
accumulate therein to fall out, rather than in the dash-pot. 

The three cuts show the manner of suspending the spools 
-and their accessibility, it being possible to remove any 
spool by simply taking out the two screws which fasten it 
io the frame, and lifting it off the lower support. 

The carbons used in arc lamps are extremely hard and 
dense. They are made from a mixture of powdered gas 
liouse coke, ground very fine, and a liquid like molasses, coal 
tar, or some similar hydro-carbon, forming a stiff, homo- 
geneous paste. This is molded into rods or pencils of the 
required size and length, or other shapes, being solidified 



Arc Lamps 1425 

under powerful hydrostatic pressure. The carbons are now 
allowed to dry, after which they are placed in crucibles or 
ovens, thoroughly covered with powdered carbon, either 
lampblack or plumbago, and baked for several hours at a 
high temperature. After cooling, they are sometimes re- 
peatedly treated to a soaking bath of some fluid hydro- 
carbon, alternated with baking, until the product is dense 
as possible, all pores and openings having been filled solid. 
Arc carbons are often plated with copper by electrolysis, 
to insure better conductivity. 

It is said that one 2,000 candlepower arc lamp will light 
in open yards 20,000 sq. ft.; in railroad stations, 14,000 
sq. ft.; in foundries and machine shops, 5,000 to 2,000 
sq. ft. Where good, even illumination is desired, it is ad- 
visable to use a greater number of smaller lamps evenly 
distributed. 

THE INCANDESCENT LAMP. 

One of the fundamental laws of electric supply is, that 
the resistance in an electric circuit should be concentrated 
at the point where energy is to be developed, and the incan- 
descent lamp is a good expression of this law, as the useful 
resistance is that which is afforded by the filaments of the 
lamp. The incandescent lamp comprises a carbon filament 
enclosed in a glass bulb from which the air has, as far as 
possible, been withdrawn, the carbon filament being sol- 
dered to the ends of small platinum wires entering the glass 
shell. Incandescent lamps can be burned either in series 
or in multiple; the multiple system being the most used. 
Series incandescent lamps are used to a considerable extent 
in the smaller towns for street lighting and also for the 
:small miniature lamps burned in series on a constant po- 



1426 Steam Engineering 

tential system, and used for decorative purposes. They are 
also used in street car lighting. 

When incandescent lamps are to be used in series, they 
should be carefully selected; there is quite a difference in 
the current consumed by different lamps, even of the same 
make, and when they are all limited to the same current 
quite a difference in candlepower raay be noticeable. Some 
will be above their rated candlepower and others below. 

The resistance- of an incandescent lamp when cold is 
very high, varying in the ordinary 16' candlepower 110 volt 
lamp from 600 to 1,000 ohms. When the lamp becomes 
heated, as when current is passing through it, the resist- 
ance reduces considerably, being in the 16 candlepower 110 
volt lamp about 220 ohms. 

The current required by the various incandescent lamps 
varies considerably for lamps of the same voltage and 
candlepower, but a good average which can be used in figur- 
ing currents is % ampere for a 16 candlepower 110 volt 
lamp and 1/4 ampere for the 220 volt 16 can(ilepower lamp. 
The amount of power, in watts, consumed by a lamp is 
equal to the voltage multiplied by the current, or W=CXE. 
A 16 candlepower 110 volt lamp taking i/^ ampere would 
consume 110X%==55 watts, while a 220 volt lamp taking 
14 ampere would consume 220X-!4:=55 watts. It will thus 
be seen that while the current and voltage may vary, the 
amount of power consumed will be approximately the same 
for all 16 candlepower lamps. Lamps are rated at a certain 
number of watts per candle, the amount varying from 3 to 4 
watts for 16 candlepower 110 volt lamps. The proper lamp 
to be used varies according to the conditions. While less 
power is consumed in a 3.1 watt lamp, the life of the lamp 
is comparatively shorter, so that the lamps will have to be 
renewed oftener. With a 4 watt lamp a greater amount of 



Incandescent Lamps 1427 

current is consumed, but the life of the lamp is longer. 
Another point of great importance in burning incandescent 
lamps is the voltage. The table below shows what effect 
variation in voltage has on the candlepower and efficiency. 

An increase in voltage increases the candlepower. This 
increases the efficiency and shortens the life as follows : 

A lamp burning at — 

Normal voltage gives 100 per cent. C. P. and consumes 3.1 Watts per C. P. 

1% above normal gives 106% C. P. and consumes 3. Watts per C. Po 

2% above normal gives 112% C. P. and consumes 2.9 Watts per C. P. 

3% above normal gives 118% C. P. and consumes 2.8 Watts per C. P. 

4% above normal gives 125% C. P. and consumes 2.7 Watts per C. P. 

5% above normal gives 132% C. P. and consumes 2.6 Watts per C. P. 

6% above normal gives 140% C. P. and consumes 2.5 Watts per C. P. 

A lamp burning at normal voltage should give its full 
candlepower at its rated efficiency. A 3.1 watt lamp burn- 
ing below its voltage loses its efficiency and candlepower as 
follows : 

If burned — 

1% below normal it gives 95% C. P. and consumes 3.2 Watts per C. P. 
2% below normal it gives 90% C. P. and consumes 3.35 Watts per C. P. 
3% below normal it gives 85% C. P. and consumes 3.5 Watts per C. P. 
4% below normal it gives 80% C. P. and consumes 3.6 Watts per C. P. 
5% below normal it gives 75% C. P. and consumes 3.75 Watts per C. P. 
6% below normal it gives 70% C. P. and consumes 4. Watts per C. P. 
10% below normal it gives 50% C. P. and consumes 4.6 Watts per C. P. 

By referring to the table it will be seen that with the 
voltage raised 3 per cent (on a 110 volt system to a little 
over 113 volts) the candlepower will increase 18 per cent,, 
or in other words, a 16 candlepower lamp would be raised 
to nearly 19 candlepower. At the same time raising the 
voltage will decrease the life of the lamp. This is shown 
in the following table where, with an increase of 6 per cent 
in the voltage, the life of the lamp is reduced 70 per cent. 
A lamp at normal voltage has 100 per cent life. 

The same lamp 1% above normal loses 18% life. 

The same lamp 2% above normal loses 30% life. 

The same lamp 3% above normal loses 44% life. 

The same lamp 4% above normal loses 55% life. 

The same lamp 5% above normal loses 62% life. 

The same lamp 6% above normal loses 70% life. 



1428 



Steam Engineering 



To obtain satisfactory results, the voltage should he 
kept constant at just the proper value. 

Considerable heat is generated in an incandescent lamp, 
so that as a general rule it is a bad plan to use paper shades 
which come very close to the bulb. Where lamps are hung 
so that there is a liability of their coming in contact with 
surrounding inflammable material, such as in warehouses 
and store-rooms, it is a good plan to enclose the lamp in a 
wire guard. 

Table 59 will prove a handy reference for estimating the 
number of lamps (8 to 50 C. P.) that can be run per horse- 
power or kilowatt. The table is figured for theoretical 
values, so that the actual horsepower or kilowatts delivered 
must be used, or else values less than those given must be 
used to allow for loss in the lines. 







Table 59 






EFFICIENCY 


OF INCANDESCENT LAMPS. 


Candlepower. 


Efficiency. 


Total Watts. 


Per 
Horsepower. 


Per Kilowatt. 


8 


3.5 


28 


26.6 


35.7 


8 


4 


32 


23.3 


31.2 


16 


3 


48 


15.5 


20.8 


16 


3.1 


50 


14.9 


20 


16 


3.5 


56 


13.3 


17.8 


16 


4 


64 


11.6 


15.6 


20 


3 


60 


12.4 


16.6 


20 


3.1 


62 


12 


16.1 


20 


3.5 


70 


10.6 


14.2 


25 


3 


75 


9.9 


13.3 


25 


3.1 


77.5 


9.6 


12 9 


25 


3.5 


87.5 


8.5 


11.4 


25 


4 


100 


7.4 


10 


32 


3 


96 


7 


10.4 


32 


3.1 


99.2 


7.5 


10 


32 


3.5 


112 


6.6 


8.9 


50 


3 


150 


4.9 


6.6 


50 


3.1 


155 


4.8 


6.4 


50 


3.5 


175 


4.2 1 5.7 . 



The first column gives the candlepower. The second 
column gives the number of watts consumed for each single 
candlepower obtained, and is called the efficiency of the 



Incandescent Lamps 1429 

, lamp. Multiply the total candlepower by the efficiency and 

you get the total number of watts consumed by the lamp. 

The fourth column shows the number of lamps per 746 

watts, and thfe last column the number of lamps per 1,000 

. watts. 

The current and watts consumed by 110 volt lamps of 
J the different candlepowers are approximately given below. 

4 candlepower 0.18 amperes, 20 watts. 

8 candlepower 0,29 amperes, 32 watts. 

16 candlepower 0.5 amperes, 55 watts. 

32 candlepower 1.0 amperes, 110 watts. 

The light given off by an incandescent lamp varies ac- 
cording to the position from which it is viewed. In some 
makes of lamps most of the light is given off directly down- 
ward, while in other lamps the maximum light is given off 
in a horizontal direction. The best lamp to use must be 
determined by the location of the lamp and the place where 
the light is required. By the use of suitable reflectors or 
shades the light can be thrown in any direction desired. 
A 16 candlepower lamp if placed seven feet above the floor 
will light up a floor space of 100 sq. ft., providing the walls 
are of a light color. If the walls are of a dull color, or if 
a bright illumination is desired more lamps should be used. 
Glass globes placed over the lamps reduce the light to a 
considerable extent, as is shown in the following table : 

Clear glass 10 per cent. 

Holophane 12 per cent. 

Opaline 20 to 40 per cent. 

Ground 25 to 30 per cent. 

Opal 25 to 60 per cent. 

PRIMARY BATTERIES. 

There are many places where a small amount of electri- 
cal power is needed, but the amount is so small, that running 
a line to the point would not pay. In such cases primary 
batteries may be used to good advantage. 



1430 



Steam Engineering 



Construction, — If a piece of zinc, and a piece of copper 
be placed in a jar containing dilute sulphuric acid, and 
not allowed to touch each other below the surface of the 
liquid, but are connected above it, by a wire, a current of 
electricity will flow through the wire, and the wire will show 
magnetic qualities. This is one of the most simple forms 
of primary battery. The current flows from the copper 
to the zinc outside of the cell, and from the zinc to the 
copper in the liquid. 



7»OS)TJVE 

Pole or 
electhode 



ATECAT/VE 



NEHATIVR 
POi£ Oft 
ELECTHOOn 




PaStJfVB 
PLATE 



Fig. 677 
names of parts of cell 

Fig. 677 shows a cell such as described above giving 
names of the difl:erent parts. The zinc plate slowly dissolves, 
and more or less hydrogen gas is thereby set free, which 
arises in the form of bubbles. Carbon has been found 
to be a good substitute for copper, in the makeup of battery 
cells. The different types of cells are classified as follows : 

Open circuit: A cell designed for intermittent work. 
Periods of work short, intervals of rest long. Usually de- 



Primary Batteries 



1431 



signed for small currents. When not in use these cells must 
be left*on open circuit. 

Semi-closed: A cell designed for fairly steady work. 
Periods of work long^ intervals of rest short. Often de- 
signed to produce heavy currents. When not in use these 
cells must be left on open circuit. 

Closed circuit: A cell designed for continuous work. 
Periods of work long^ intervals of rest very short. "Flsually 
designed for very small currents. Almost impossible to 
design so as to produce m^uch current. When not in use 
they must be left on closed circuit. • 



^VT\A. 




^i-^-€l& 



Si'S^* 



Fig. 678 
carbon cylinder cell 



Polarization prevented : Cell so designed that no hydro- 
gen gas is produced by chemical action of cell. 

Polarization cured : Cell produces hydrogen^ but a 
chemical placed in the cell turns the hydrogen to water 
which is harmless. 

Polarization delayed : Cell has very large and absorbent 
negative plate. 

The Carbon Cylinder Cell. — These are sold under the 
name of Law, Samson, Hercules, etc. It is an open cir- 



1432 



Steam Engineering 



cuit^ polarization delayed type. They give a pressure of 
1.5 volts and have a resistance of 1 to 2 ohms. Two of 
them are shown in Fig. 678. 

The carbon element is made with as large a surface as 
possible. Carbon and charcoal have a remarkable power 
of absorbing gases. A cubic inch of charcoal will condense 
and absorb 20 to 30 cubic inches of gas. 

The'^inc element is a rod and the fluid a strong solution 
of sal ammoniac in water. The scientific name of this 
chemical is ammonium chloride. 




Fig. 679 
carbon cylinder cell with depolarizer 

The action of the cell dissolves the zinc, forming zinc 
chloride, which dissolves in the water. A little ammonia 
•and hydrogen gases are set free. The ammonia is dis- 
solved by the water and the hydrogen absorbed by the 
carbon. 

In time the carbon gets soaked full of hydrogen, and 
to restore the cell it should be taken out and boiled in water 
for an hour. 

These should only be used for call bells in offices or such 
unimportant work. 

Ledanche Cell. — This is an open-circuit, polarization 
cured type. They are made in several forms. Voltage 1.5 



Primary Batteries 



1433 



and resistance 1 to 4 ohms. Uses sal ammoniaC;, zinc and 
carbon. 

The carbon cylinder cell is sometimes modified to the 
Leclanche type by making the carbon element with a bot- 
tom and no opening in the sides. This carbon can, or 
bucket is filled with lumps of black oxide of manganese 




Fig. 680 
ordii^ary leclanche cell 



Fig. 681 
elements of the 
gonda-leclanche cell 



(manganese dioxide). The zinc is made in a cylindrical 
form, surrounding the carbon. This cell is shown in Fig. 
679. 

The hydrogen is absorbed by the carbon but the man- 
ganese dioxide, being in contact with the carbon, gives up 
half of its oxygen to the hydrogen forming water, while it 
is reduced to manganese monoxide. 



1434 Steam Engineering 

This cell is useful for call bell work, operating magnets 
on interlocking machines^ running tell-tales on interlock- 
. ing boards^ and such other intermittent light work. 

There is an older form of Leclanche cell shown in Fig. 
680^ where the carbon is placed in a cup of unglazed earthen 
ware (like a j^ellow flower pot) called a porous cup. The 
manganese is packed around the carbon slab. This form 
does not give such a large current as the cell in Fig. 679 
because its resistance is high^ often as much as four or five 
ohms. 

A much used form of the Leclanche cell is the Gonda 
cell. The elements are shown in Fig. 681. 

Here the manganese is powdered^, mixed with cheap mo- 
lasses^ then by heat and pressure formed into slabs. These 
are attached to the carbon plates by rubber bands. 

The bother and resistance of the porous cup is avoided. 

The usual charge of a Leclanche type cell is a generous 
quarter pound of sal ammoniac dissolved in sufficient water 
to fill the jar two-thirds full after elements are in place. 

The Gravity Cell. — This is a closed circuit cell with 
polarization prevented. It is very much used for telegraph 
circuits^ operating the electrical devices in the lock and 
block signals, the motors in automatic signals and generally 
around interlocking plants. Its pressure is 1 volt and its 
current capacity rather low for its resistance is 3 or 4 ohms. 

This cell is made in many forms called Bluestone cell, 
crow-foot battery, Lockwood cell, etc. 

The parts of a gravity cell are shown in Fig. 682, and 
the assembled cell in Fig. 683. 

The glass jars should be about 7 inches high and 6 inches 
in diameter. The zinc is cast in a shape so as to be easily 
suspended from the edge of the jar. The form shown is 
called a crow-foot zinc. It weighs about 3 pounds. 



Primary Batteries 1435 

The copper element shown on left of Fig. 682 is made 
of three sheets riveted together at center and then spread 
out as shown. The rubber covered wire must be at- 
tached to the copper element by riveting. If soldered the 
joint would be eaten away by electrical action. 

To set np a cell of ordinary size which holds about 0.8 




Fig. 682 
elements of gravity cell and jar 

gallons of liquid, make two solutions, one of copper, the 
other of zinc. 

Zinc solution : Pint and a half of pure soft water and 
10 oz. of crystallized sulphate of zinc (white vitriol). Mix 
until dissolved and let it stand half a day in a glass jar. 

Copper solution: Two and a half pints of soft water, 
4 ozs. of crystallized sulphate of zinc, 8 ozs. crystallized 



1436 



Steam Engineering 

Mix and let stand a 



sulphate of copper (blue vitriol). 
few hours in a glass jar. 

Dip edge of battery jar for an inch in melted paraffin 
and let it cool. 

Place the parts in jar as in Fig. 683 and pour jar nearly 
three-fourths full of the zinc solution. Place it at once 




Fig. 683 
gravity cell ready for use 



in the spot where it is to be used and pour in the copper 
solution. 

Insert a glass funnel in the top of a piece of %-inch 
rubber tubing. Hold funnel so that lower end of the tube 
will be in the middle of the jar and just a little above the 
bottom. 



Primary Batteries 



1437 



Pour in the copper solution slowly until the copper ele- 
ment is completely covered. Place the cell into service im- 
mediately. 

This cell will show a sharply defined line between the 
blue copper solution and the colorless zinc solution. This 
separation of solutions is essential to the celFs health. 
Leaving the circuit open for any length of time will allow 
the solutions to mix and spoil the cell. 
, The action of the cell is such that no hydrogen is per- 
manently formed. The zinc is steadily dissolved into the 



r\ 




Fig. 684 
long service copper element for gravity cell 

zinc solution, setting free some hydrogen. This forms with 
the copper sulphate, sulphuric acid and metallic copper. 
The sulphuric acid dissolves more zinc, while the copper 
plates itself on the copper element at the bottom of jar. 

The zinc is consumed and the copper plate grows larger. 

The effect of continued action is to increase the strength 
of the zinc solution so that it tends to settle to bottom of jar. 

The copper being taken out, bit by bit, from the copper 
solution this latter gets lighter in weight and tends to rise 
being pushed up by the zinc solution. 



1438 Steam Engineering 

If the blue solution of copper sulphate ever touches the 
zinc it will copper plate it at once. The cell will then have 
two copper elements and stop working. 

Cells should be given some attention, and clever manage- 
ment will keep a gravity cell working continuously for an 
almost indefinite time. 

As helps in the maintenance of cells two improvements 
have been made. 

The form of copper element shown in Fig. 684 is better 
when heavy currents are not needed. It is a copper ribbon 




Fig. 685 
d'ixfrevilles wasteless ZINtJ 

4 feet locLg and V2 an inch wide^, coiled like a clock spring. 
Zincs shaped like Fig. 685 are used until the prongs are all 
eaten off. A new one is then put in service and the old 
one jammed into the bottom of the new one as shown in 
Fig. 686. 

These zincs are hung from a spring clip shown in Fig. 
687, which lays across the top of the jar. The stud on 
the zinc makes a tight friction fit with the hole in the 
hanger, due to the springiness of the metal. 



Primary Batierics 



1439 



To keep cells in order a hard rubber syringe with the 
nozzle at right angles to barrel^ holding about a pint^ and a 
hydrometer should be obtained. 

The hydrometer (Fig. 688) is a hollow glass float loaded 
with shot so as to float upright. The heavier a liquid the 
more of the stem sticks up above the surface. 

These h5^drometers are graduated on stem in actual spe- 
cific gravities or in degrees Baume (pronounced Bomay). 
One with a stem about two inches long graduated from 15° 
to 40° Baume^ or from 1.11 to 1.40 specific gravity, is best 
for battery work. 




Fig. 686 
using up old zincs 

The first signs of exhaustion in the cell will be a fading 
of the deep blue color of the copper solution and a lowering 
of the line of separation between blue and white liquids. 

When this occurs drop in about an ounce of copper sul- 
phate in lumps. Be sure the lumps fall to the bottom. 
There will always be a lot of fine powder at the bottom 
of the copper sulphate barrel. Use this for making up new 
cells when possible. If too much accumulates for this pur- 
pose, make a saturated solution of it in water. 

A saturated solution is one where the water has dis- 
solved all it possibly can of the chemical, and leaves some 



1440 



Steam Engineering 



yet undissolved on bottom of jar after repeated stirring. 

Place this in cells showing signs of exhaustion in same 
way as the copper solution was placed in a newly set up 
cell. 

The zinc solution should be tested as frequently as possi- 
ble. Once in two weeks is not too often. Drop the hydrom- 
eter gently in. Should it read 1.15 draw some out with 
syringe and replace by fresh water. 

Do not let it go below 1.10. If you have a Baume scale 
these numbers are 20 and 15 degrees. Throw all the re- 
moved zinc in a wooden tub^ whether from working cells or 
from old cells^ to be renewed. 




=^o 



Fig. 687 



Keep half a dozen pieces of metallic zinc in this tub. 
Any copper in this solution, mixed by celFs action, will 
turn to a reddish brown curd which can be filtered out. 
Eeduce the clear liquid to 1.10 and use in making up new 
cells. 

Watch your zinc. Should any brown hangers develop 
on it, detach them with a bent wire and let them fall to 
bottom of cell. 

In time, in spite of all care, the zinc in a cell gets red- 
dish brown all over. It is now time to give a complete 
overhauling. 

Take the cell out of service. Syphon off zinc solution into 
the tub. Lift zinc out carefully and at once scrub clean 
with a wire brush. Wash and replace in another cell at 
once or dry thoroughly and keep dry until needed. 



Primary Batteries 



1441 



Syphon off the rest of the liquid into another wooden tub 
and use after filtering as copper solution to make up new 
cells. 

Any lumps of copper sulphate in the bottom take out, 
rinse, and put in other cells. 




Fig. 688 
hydrometer with baume scale 



The mud in bottom of cells and in the zinc solution tub 
should be dried and sold to brass founders as "^^battery mud/^ 

The copper plates taken from cells should be kept com- 
pletely covered with water, wire and all, until needed again. 



1442 



Steam Engineering 



When they get too heavy and cumbersome sell them^ as 
they are an especially pure form of copper. 

Xever leave gravity cell on open circuit; the liquids will 
mix. 

Tlie Fuller Cell. — Semi-closed circuit type, for heavy 
duty. Long periods of work with little rest. 

Polarization cured. Pressure 2 volts, resistance 0.5 ohms. 
Cell shown in Fig. 689. 

These cells are carbon and zinc, and since the chemical 




Fig. 689 
fuller cell 

which converts the hydrogen to water will attack the zinc, 
a porous cup is used. 

The carbon or the zinc can be placed in the porous cup, 
but the zinc usually is. A tablespoonful of mercury is 
placed in bottom of porous cup, the zinc set in and the cup 
filled with very dilute sulphuric acid (1 acid, 50 water). 
The carbon is then placed in the outer jar, the porous cup 
being also in, and the outer jar filled three-quarters full 
of battery fluid or electropqin. 

This is composed of 4 ozs. of bichromate of soda, 11/4 
pints of boiling water, mixed and cooled; then while slowly 



Primary Batteries 



1443 



stirring add little by little 3 ozs. siilphnric.aeid taken out 
of a carbon (not diluted). Never pour water into acid. 

The bichromate of soda has so much oxygen in it that 
it will turn the hydrogen to water^ changing itself to chro- 
mate of soda. 

When the interior of the porous cup gets dark green 
colored a cup should be soaked in 1 to 50 acid for an hour 




Fig. 690 
oxide plate of edison-lalande cell 



and then mercury placed in bottom and zinc set in. Sim- 
ply take out old cup and insert new one in its place. 

The old zinc should be cleaned^ porous cup washed and 
then boiled in water and both placed in stock. 

These cells should be left on open circuit when not in use. 
They are very powerful, but nasty to handle and not as 
cheap as the gravity cell. When the electropoin gets green- 
ish it soon becomes exhausted, then throw it awav. Cold 



1444 Steam Engineering 

battery rooms, pr pits affect this cell less than the gravity 
cell. 

Edison-Lalande Cell, — This is a semi-closed type with 
polarization cured. It has a resistance of 0.2 ohms and a 
very low voltage, 0.7^ but is a bull dog for holding on. 
It will, when set up, start in to deliver a heavy current and 
keep at it until all its chemicals are used up. It needs no 
attention and is built sp that you can not give any. 

When it stops take out the copper and sell it, throwing 
everything else out. Clean up the jar and fit out again. 

The cell uses zinc and oxide of copper plates immersed in 
a solution of caustic potash. The oxide plate is shown in 
Fig. 690 and the complete cell with a glass jar in Fig. 691. 
Porcelain jars are usually furnished. 

The caustic potash comes in sticks sealed up in a tin 
can. 

Place the elements in jar and fill with water to about 
one inch of the top. Take out the elements and put in the 
sticks of potash. 

Stir constantly while dissolving, for it gets very hot and 
might crack the jar. Be very careful not to get caustic 
potash on your flesh. It not only burns terribly, but makes 
a wound which is very hard to heal. 

If you buy potash by bulk, make the solution up to 1.33 
on specific gravity scale or 38° on the Baume scale. 

Place the zinc and copper oxide elements in the jar, see- 
ing that they are properly separated by the hard rubber 
buffers. Pour the bottle of oil over the top of solution and 
place cover on. 

If buying oil by bulk, get a heavy paraffin oil which 
will read 1.46 specific gravity or 48° Baume and pour a ^4 
inch layer on each cell 



Primary Batteries 



1445 



These are good cells^ but any sulphuric acid or caustic 
potash cell is a nasty thing to handle. 

The action of the cell dissolves the zinc, setting free 
hydrogen, which is changed to water by the copper oxide, 
which is reduced to pure copper by giving up the oxygen 
in it. 




Fig. 691 
edison-lalande cell 

Dry Batteries. — A dry battery is one which has its elec- 
trolyte disseminated through some solid material through 
which it can diffuse itself. Plaster of Paris and gelatinous 
compounds have been used for the solid part. The usual 
construction is on the basis of the plaster of Paris combin- 
nation. 



1446 



Steam Engineering 



The outer cup is made of zinc^ and acts as the positive 
electrode. Over it is slipped a strawboard tube. The object 
is to prevent the zinc of two batteries from touching each 
other so as to establish a wrong connection. The negative 
electrode is a plate of carbon. This is placed in the center 
of the zinc, and is so supported as not to touch it in any 
place. Carbon and zinc both carry binding posts. The fill- 
ing varies. The following is used in the Burnley cell : 

A wooden plunger or template, somewhat larger than the 
carbon^ is inserted, and the following mixture introduced : 




Fig. 692 

DRY CELL 

Ammonium chloride^ zinc chloride, 1 part of each, plaster 
of Paris^ 3 parts, flour 0.87 part, water 2 parts. After this 
has set a little^ the wooden template is withdrawn^ the car- 
bon is inserted in the cavity left by its withdrawal, and the 
space left unfilled is filled with the following mixture. 
Ammonium chloride, zinc chloride, manganese binoxide, 
granulated carbon, flour, 1 part of each, plaster 3 parts, 
water 2 parts. The electromotive force of this cell is 1.4 
volts, its resistance 0.3 ohm. 

The Gassner dry cell has as negative a cylinder made of 
a mixture of carbon and manganese dioxide. The filling 



storage Batteries 1447 

^ompositioIl is as follows : Zinc oxide, ammonium chloride, 
and zinc chloride;, 1 part each, plaster of Paris 3 parts, 
water 2 parts. 

For the Meserole dry battery^, there are mixed the fol- 
lowing : Graphite, slacked lime, arsenious acid, and glucose 
01 dextrine, 1 part each, carbon and manganese binoxide, 
3 parts each. The mixture is finely pulverized and rubbed 
up in a saturated solution of ammonium chloride and sodium 
chloride (common salt) with one-tenth its volume of a 
solution of mercuric chloride and an equal volume of hydro- 
chloric acid. These constituents are intimately mixed and 
poured into the zinc cup. 

Dry batteries are sealed with pitch. A hole is sometimes 
left for the escape of gas. 

STORAGE BATTERIES. 

The storage cell is rapidly pushing the primary battery 
aside in signal and fire alarm work on account of : 

(1) Its high voltage. 

(2) Its great current capacity. 

(3) The lowering of total battery expense if used for 
several years. 

(4) Its steadiness of action. 

Storage cells are used in train lighting to furnish light 
when train is not in motion, and to steady the supply of 
current. 

They are used in some cases to furnish the power to 
operate switches on locomotives and motor cars. 

In power houses they offer a reserve supply of power, 
and act as a steadier of the load on the generators. 

The simplest storage cell would be two strips of lead 
immersed in dilute sulplmric acid. When current is sent 



1448 



Steam Engineering 



through them one plate turns a dark brown color^ md the 
other a grey color. After an hour^s passage of current 
reverse the connection and charge the other way. The 
plates will change color — the grey one becoming brown 
and the other one grey. 

If this charging first in one direction, and then in the 
other be kept up, you will notice that after each reversal 
of the current through the cell the acid is quiet but soon 




begins to gas or boil. This is the signal to reverse the cur- 
rent as the cell is charged. 

When the cell takes several hours to gas it is in condi- 
tion to use. 

After one of the reversals continue to charge until cell 
has gassed about fifteen minutes. Eemove the charging 
wires and connect to anything you wish to run. About 
70% of the power you put into the cell can now be taken 
out. 

You may now use this as a storage cell, charging it up 



storage Batteries 1449 

till it gasses^ and then using the accumulated electricity as 
you please. 

You always lose 30% but you have the advantages of 
portability^ and ability to work when engines are shut down. 

In time you will notice that the lead plates become 
spongy and should the cell be used long enough the plates 
will finally crumble and break. You will notice that the 
more spongy the plates become the greater a charge they are 
capable of holding. 

In fact^ just before your battery goes to pieces its ca- 
pacity is the greatest. 

To make a commercially practical cell we would proceed 
thus : 

The lead plates would be replaced by grids as shown in 
Pig. 693 or by grooved plates as in Pig. 694. 

Litharge and sulphuric acid is mixed to a stiff paste 
and the grids or grooved plates plastered with the paste and 
stood up to dry. This makes a negative plate. 

Using a paste of red lead and sulphuric acid the positive 
plates are formed in the same way. 

The objection to a storage cell using these plates is that 
after very little use they go to pieces. The changing of the 
red lead to the brown oxide^ and the changing of the 
litharge to spongy lead is accompanied by a swelling and 
shrinking of the material. This loosens up the pasted mass 
and it begins to fall out. 

Most of the ingenuity of inventors has been concentrated 
on making plates which would hold the active materials 
firmly and continually. 

Perhaps one of the best lead-lead (i. e. lead for both 
plates) is the Electric Storage Battery Company^s Chlor- 
ide Cell 



1450 



Steam Engineering 



This cell is shown in Fig. 695. Its method of manufac- 
ture is interesting and is practically as follows : 

The first thing is to get finely divided lead which is 
made by directing a blast of air against a stream of the 
molten metal^ producing a spray of lead which upon cool- 
ing falls as a powder. This powder is dissolved in nitric 





Fig. 694 
grooved lead plates 

acid and precipitated* as lead chloride on the addi- 
tion of hydrochloric acid. This chloride washed and dried 
forms the basis of the material which afterwards becomes 
active in the negative plate. The lead chloride is mixed 
with zinc chloride^ and melted in crucibles^ then cast into 



*Tnrned back to a solid. 



storage Batteries 



1451 



small blocks or tablets about % inch square and of the 
thickness of the negative plate, which according to the size 
of the battery varies from % inch to -{q inch. These tablets 
are then put in molds and held in place by pins, so that 
they clear each other 0.2 inch and are at the same distance 
from the edges of the mold. Molten lead is then forced 
into the mold under about seventy-five pounds pressure, 
completely filling the space between the tablets. The result 




Fig. 695 
chloride accumulator 

is a solid lead grid holding small squares of active material. 
The lead chloride is then reduced by stacking the plates in 
a tank containing a dilute solution of zinc chloride, slabs 
of zinc being alternated with them. The assemblage of 
plates constitutes a short-circuited cell, the lead chloride 
being reduced to metallic lead. The plates are then thor- 
oughly washed to remove all traces of zinc chloride. 



1452 Steam Engineering 

A later form of negative plate consists of a "pocketed^' 
grid, the opening being filled with a litharge paste; this is 
then covered with perforated lead sheets, which are soldered 
to the grid. The positive plate is a firm grid, composed of 
lead alloyed with about 5% of antimony, about -^q inch 
thick, with circular holes |f inch in diameter, staggered so 
that the nearest points are .2 inch apart. Corrugated lead 
ribbons f f inch wide are then rolled into close spirals of f f 
inch in diameter, which are forced into the circular holes of 
the plate. By electro-chemical action these spirals are 
formed into active material, the process requiring about 
thirty hours; at the same time the spirals expand so that 
they fit still more closely in the grids. This form of posi- 
tive is known as the Manchester Plate. 

In setting up the cells the plates are separated from each 
other by special cherry wood partitions, the perforations 
being connected by vertical grooves to facilitate the rising 
of the gases. Sometimes glass rods are used as separators. 

There are ten sizes of cell, the smallest containing three 
plates 3 by 3 inches, and the largest having seventy-five 
plates 151/^ by 30% inches, ranging in capacity from 5 to 
12,000 ampere-hours, and in weight from 5% to 5,800 lbs. 
The smaller sizes are provided with either rubber or glass 
jars, and the larger one with lead-lined tanks. 

In the lead-lead cells the negative plates deteriorate in 
capacity, while the positive plates increase in capacity with 
continued use. 

To even things up, the two end plates are made negative 
and they then alternate, thus giving one more negative plate 
per cell. 

A lead- zinc cell is made by the United States Battery Co. 
It is Rhown in Pig. 696. 



storage Batteries 1453 

The positive plate is of perforated lead sheets riveted 
together with lead rivets, and formed by the slow process 
of charging and reversal as previously described. The negar 
tive element is a zinc amalgam which swells up when 
■charged. 

This amalgam lies on bottom of jar, while the lead ele- 
ment hangs over it. 

The pressure given by these cells is a little higher than 
a lead-lead cell, and they weigh less for the same capacity. 
Por signal work they are excellent^ while for reserve power 




Fig. 696 
lead-zinc storage battery 

use, the lead-lead cell is preierred as being better under 
such severe conditions. 

The Edison Cell uses grids of nickel plated iron, the grids 
being filled with small nickel plated steel boxes which are 
perforated with very small holes. 

The boxes in positive plate are filled with oxide of nickel 
and pulverized carbon, the negative boxes being filled with 
oxide of iron and pulverized carbon. 

The carbon in each case is merely to render material a 
Abetter conductor. 



1454 Steam Engineering 

A 20% solution of caustic potash is used in a nickel plated 
steel vessel. 

The advantage of this cell is its lightness and ability to 
stand the most reckless abuse. For railway work it is no* 
better than any other cell and fts price puts it out of con- 
sideration. 

UNDEEWEITER^S RULES 

1. Generators, 

a. Must be located in a dry place. 

It is recommended that water-proof covers be provided, 
which may be used in case of emergency. 

If generators are allowed to become wet, there is likely 
to be more or less charring or burning of the cotton insula- 
tion of the wires, due to the fact that shellaced cotton will 
conduct electricity when wet. The current leaking over this 
moist conducting path, the resistance of which is being con- 
stantly decreased by the formation of copper salts by elec- 
trolytic action, may eventually develop excessive heat or 
even fusion of some of the metallic parts. 

b. Must never be placed in a room where any hazardous 
process is carried on, nor in places where they would be 
exposed to inflammable gases or flyings of combustible 
materials. 

Any generator, if badly designed, improperly handled, 
poorly cared for or overloaded, is liable to produce sparks, 
which may be of sufficient intensity to set fire to readily in- 
flammable gases, dust, lint, oils and the like. 

c. Must, when operating at a potential in excess of 550 
volts, have their base frames permanently and effectively 
grounded. 

Must, when operating at a potential of 550 volts or less, 
be thoroughly insulated from the ground wherever feasible. 



Underwriters' Rules 1455 

Wooden base frames used for this purpose^ and wooden 
floors which are depended upon for insulation where, for 
any reason it is necessary to omit the base frames, must be 
kept filled to prevent absorption of moisture, and must be 
kept clean and dry. 

Where frame insulation is impracticable, the Inspection 
Department having jurisdiction may, in writing, permit its 
omission in which case the frame must be permanently and 
effectively grounded. 

A high potential machine should be surrounded by an in- 
sulated platform. This may be made of wood, mounted on 
insulating supports, and so arranged that a man must al- 
ways stand upon it in order to touch any part of the 
machine. 

In case of a machine having an insulated frame, if there 
is trouble from static electricity due to belt friction, it 
should be overcome by placing near the belt a metallic comb 
connected with the earth, or by grounding the frame 
through a resistance of not less than 300,000 ohms. 

By ^^ground^^ is to be understood the earth, walls or floors 
of masonry, pipes of any kind, iron beams, and the like. 

If frame insulation is not provided, a slight fault in the 
insulation of the magnet or armature coils is likely to 
ground the electric system, and a short-circuit will then oc- 
cur the instant another ground occurs at any point on the 
system. 

The reason for requiring a positive ground wherever 
frame insulation is impracticable, is to provide a definite 
path for leak currents, and thus prevent them from escap- 
ing at points where they might do harm. A good ground 
can be made by firmly attaching a wire to the dynama 
frame and to any main water pipe that is thoroughly con- 
nected with underground pipes. The wire should not be 



1456 Steam Engineering 

smaller than No. 6 B. & S. gage and should be securely 
attached to the pipe by soldering it to a brass plug screwed 
into" a fitting/ or by binding it under a heavy split clamp, or 
by any other equally thorough method. With direct- con- 
nected units, the engine or water-wheel would generally 
furnish a sufficiently good ground. 

It is best to provide a solid timber base-frame, even with 
a wooden floor, for it is difficult to be sure that even a dry 
floor will furnish perfect insulation, by reason of the many - 
nails driven through it, the pipe hangers likely to be screwed 
into its under side and the many other possibilities of me- 
tallic connection to the ground. For the same reason, care 
should be taken that the bolts which hold the generator in 
place do not pass way through the base-frame, so as to come 
in contact with the floor. 

The base-frame should raise the generator several inches 
above the floor level, as a raised frame is more easily kept 
free from metal dust, dampness, etc., which may afford an 
opportunity for the escape of current to the ground. A 
hard and durable finish for the timber can be made by sev- 
eral coats of linseed oil, and a finish coat of shellac or hard 
varnish. 

When generators are direct-connected to engines or water^ 
wheels, it is necessary to use an insulating coupling if the 
frames are to be insulated from the ground. The insulation 
of such couplings is not entirely reliable, as the vibrations, 
shocks and constant strain of driving, together with oil and 
dirt, are very liable to destroy the insulating material. 

d. Constant potential generators, except alternating 
current machines and their exciters, must be protected from 
excessive current by safety fuses or equivalent devices of 
approved design. 



Underwriters' Rules 1457 

For two-wire, direct-current generators^ single pole pro- 
tection will be considered as satisfying the above rnle, pro- 
vided the safety device is located in the lead not connected 
to the series winding. When supplying three-wire systems, 
the generators should be so arranged that these protective 
devices will come in the outside leads. 

For three-wire, direct-current generators, a safety device 
must be placed in each armature, direct-current lead, or a 
double pole, double trip circuit breaker in each outside gen- 
erator lead, and corresponding equalizer connection. 

In general, generators should preferably have no exposed 
live parts, and the leads should be well insulated and thor- 
oughly protected against mechanical injury. This protec- 
tion of the bare live parts against accidental contact would 
apply also to any exposed, uninsulated conductors outside 
of the generator, and not on the switchboard unless their 
potential is practically that of the ground. 

Where the needs of the service make the above require- 
ments impracticable, the Inspection Department having 
jurisdiction may, in writing, modify them. 

If this protection is not provided, an accidental short- 
circuit across the bus-bars, or the exposed metal parts of 
the main switch on the switchboard is liable to result in the 
burning out of the armature. 

Owing to inherent qualities possessed by the alternating 
current generator it is not considered necessary to protect 
it, especially as the quick opening of a protective device 
would be liable to give rise to momentary high voltage on 
the system. 

e. Must each be provided with a nameplate, giving the 
maker^s name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 



1458 Steam Engineering 

The name-plate shows exactly what the machine was de- 
signed for. Such information is often of great convenience, 
and also tends to prevent overrating^ either from ignorance, 
or from a deeire - to magnify the merits of a machine in 
order to help a sale. 

/. Terminal blocks when used on generators must be 
made of approved non-combnstible^ non-absorptive, insu- 
lating material^ siioh as slate, marble or porcelain. 

A reliable voltmeter should be provided on the switch- 
board, and it is best to have it so arranged as to show the 
voltage not only between the wires of opposite polarity, 
but also between each wire and the earth, thus serving as 
a very sensitive ground detector. 

It is also advised that a reliable ammeter be provided with 
every constant-potential generator, and that it be clearly 
marked to indicate the full load of the machine. This in- 
strument measures the amount of current given out by the 
generator and shows instantly if there is any undue load, 
such as would be produced if too many lamps were put in 
circuit, or if there were serious leakage of current at any 
point on the system. It is always desirable to have all 
generator ammeters on a switchboard so graduated that a 
full scale deflection corresponds to the same degree of over- 
load on each, so that when several machines of different 
sizes are running in parallel, each machine will be doing its 
share of the work when the ammeter pointers are in similar 
positions. 

2. Conductors. 

From generators to switchboards, rheostats or other in- 
struments, and then to outside lines : 

a. Must be in plain sight or readily accessible. 

Wires from generator to switchboard may, however, be 
placed in a conduit in the brick or cement pier on which the 



Undertvriters' Rules 1459 

generator stands, provided that proper precautions are taken 
to protect them against moisture and to thoroughly insulate 
them from the pier. If lead-covered cable is used;, no fur- 
ther protection will be required, but it should not be al- 
lowed to rest upon sharp edges which in time might cut 
ipto the lead sheath, especially if the cables were liable to 
vibration. A smooth runway is desired. If iron conduit is 
provided, double braided rubber-covered wire will be satis- 
factory. 

Main conductors in immediate connection with the source 
of power must be treated as especially dangerous, because 
the whole capacity of the system would be concentrated in 
them should an arc start, or an accidental short-circuit be 
made between them. 

b. Must have an approved insulating covering as called 
for by rules in Class "C^^ for similar work, except that 
in central stations, on exposed circuits, the wire which is 
used must have a heavy braided, non-combustible outer cov- 
ering. 

Bus-bars may be made of bare metal. 

Eubber insulations ignite easily and burn freely. Where 
a number of wires are brought close together, as is generally 
the case in dynamo rooms, especially about the switchboard, 
it is therefore necessary to surround this inflammable ma- 
terial with a tight, non-combustible outer cover. If this is 
not done, a fire once started at this point would spread 
along the wires, producing intense heat and a dense smoke. 
Where the wires have such a covering and are well insu- 
lated and supported, using only non-combustible materials, 
it is believed that no appreciable fire hazard exists, even 
with a large group of wires. 

Flame proofing should be stripped back on all cables a 
isufficient amount to give the necessary insulation distances 



1460 Steam Engineering 

for the voltage of the circuit on which the cable is used. The 
stripping back of the flame proofing is necessary on account 
of the poor insulating qualities of the flame proofing mate- 
rial now available. Flame proofing may be omitted where 
satisfactory fire proofing is accomplished by other means, 
such as compartments, etc. 

i It is also recommended that all live parts of the switch- 
board, such as bus-bars and other conductors, be protected 
against accidental contact as far as practicable by suitable 
insulation, which. shall be ^^flame proofs or ^^slow-burning^^ 
and designed to withstand a reasonable amount of abrasion. 
The chances of accidental short-circuits may thereby be 
greatly reduced. Insulated cable for bus-bars and connec- 
tions is excellent for this purpose. However, the conduc- 
tors could be wrapped or taped if this should be found 
more convenient, but this method should never be used 
unless it can be done well. Due to the possibly rather low 
insulating properties of most fireproofing compounds as 
used, special precautions would be necessary on high-voltage 
circuits to prevent current leakage over the outer fireproof ed 
•covering. 

c. Must be kept so rigidly in place that they cannot 
come in contact. 

It is necessary, also, to protect the wires against acci- 
dental blows from belt, or from ladders, etc., in the hands 
of careless workmen. 

d. Must in all other respects be installed with the same 
precautions as required by rules in Class "G^^ for wires car- 
rying a current of the same volume and potential. 

e. In wiring switchboards the ground detector, volt- 
meter, pilot lights and potential transformers must be con- 
nected to a circuit of not less than No. 14 B. & S. gauge 



Underwriters' Rules 1461 

wire that is protected by an approved fuse, this circuit is 
not to carry over 660 watts. 

For the protection of instruments and pilot lights on 
switchboards, approved N. E. Code Standard Enclosed 
Fuses are preferred, but approved enclosed fuses of other 
designs of not over two (2) amperes capacity, may be used. 

Voltmeter switches having concealed connections must 
be plainly marked, showing connections made. 
: 3. Switchboards. 

a. Must be so placed as to reduce to a minimum the 
danger of communicating fire to adjacent combustible ma- 
terial. 

It is often necessary, also, to protect the wires against 
accidental blows from belt, or from ladders, etc., in the 
hands of careless workmen. This may be done in about 
the same manner as is recommended for wires on side walls. 

Special attention is called to the fact that switchboards 
should not be built down to the floor, nor up to the ceiling. 
A space of at least ten or twelve inches should be left be- 
tween the floor and the board, except when the floor about 
the switchboard is of concrete or other fireproof construc- 
tion, and a space of three feet, if possible, between the ceil- 
ing and the board, in order to prevent fire from communi- 
cating from the switchboard to the floor or ceilings and also 
to prevent the forming of a partially concealed* space very 
liable to be used for storage of rubbish and oily waste. 

Great care in designing and locating a switchboard is 
necessary for several reasons; the rheostats, measuring in- 
struments, fuses, etc., are possible sources of fire; there is 
a considerable number of bare live parts on the ordinary 
board which afford good opportunity for accidental short- 
circuits; and there is frequently a large amount of power 



1462 Steam Engineering 

available at the board to quickly follow up any trouble at 
this point. 

&. Must be made of non-combustible material or of 
hardwood in skeleton form^ filled to prevent absorption of 
moisture. 

If wood is used all wires, and all current carrying parts 
of the apparatus on the switchboard must be separated 
therefrom by non-combustible^ non-absorptive insulating 
material. 

Switchboards of slate or marble are now- mostly used. A 
slate board complete is but little more expensive than a 
properly wired and equipped wooden board in skeleton 
form. The non-combustible board is undoubtedly prefer- 
able, and is therefore strongly recommended, especially for 
the larger equipments. 

c. Must be accessible from all sides when the connec- 
tions are on the back^ but may be placed against a brick 
or stone wall when the wiring is entirely on the face. 

If the wiring is on the back, there should be a clear space 
of at least eighteen inches between the wall and the ap- 
paratus on the board, and even if the wiring is entirely on 
the face, it is much better to have the board set out from the 
wall. The space back of the board should not be closed in, 
except by grating or netting either at the sides, top or bot- 
tom, as such an enclosure is almost sure to be used as a 
closet for clothing or for the storage of oil cans, rubbish, 
etc. An open space is much more likely to be kept clean, 
and is more convenient for making repairs^ examinations, 
etc. 

d. Must be kept free from moisture. 

Water on a switchboard is liable to produce serious 
trouble, as it is almost certain to start leaks over the sur- 
face of the insulating coverings on the wires and over the 



Underwriters' Rules 1463 

boara itself ; for water-soaked insulators, or a film of water 
on a non-absorptive insulator, like glass, porcelain or hard 
rubber^ will conduct electricity to some extent. By elec- 
trolytic action this leakage current will form salts of copper 
over the surface of the insulating parts, and as these salts 
are good conductors, the leakage current will be increased, 
resulting in the inevitable destruction of the weakest part, 
be it insulation, wire or dynamo. Under such conditions 
there would also be great danger of the attendant receiving 
severe shocks. 

e. On switchboards the distances between bare live parts 
of opposite polarity must be made as great as practicable, 
and must not be legs than those given for tablet-boards. 

4. ResiMance Boxes and Equalizers. 

a. Must be placed on switchboard, or if not thereon, at 
a distance of at least one foot from combustible material, 
or separated therefrom by non-combustible, non-absorptive 
insulating material such as slate or marble. 

This will require the use of a slab or panel of non-com- 
bustible, non-absorptive insulating material such as slate 
or marble, somewhat larger than the rheostat, which shall 
be secured in position independently of the rheostat sup- 
ports. Bolts for supporting the rheostat shall be counter- 
sunk at least % inch below the surface at the back of the 
slab and filled. For proper mechanical strength, slab 
should be of a thickness consistent with the size and weight 
of the rheostat, and in no case to be less than Yo inch. 

If resistance devices are installed in rooms where dust 
or combustible flyings would be liable to accumulate on 
them, they should be equipped with a dustproof face-plate. 

Resistance boxes should be considered as stoves, which 
under some conditions may become red hot, and from which 



1464 Steam Engineering 

drops of heated metal may fall^ or even be thrown some 
distance. 

Motor-starting rheostats, arc lamp compensators, elec^ 
trie heaters and the like would all come under this rule 
unless so designed as to make these precautions unneces- 
sary for the desired safety. 

&. Where protective resistances are necessary in con- 
nection with automatic rheostats, incandescent lamps may 
be used, provided that they do not carry or control the 
main current nor constitute the regulating resistance of 
the device. 

When so used, lamps must be mounted in porcelain re- 
ceptacles upon non-combustible supports, and must be so 
arranged that they cannot have impressed upon them a 
voltage greater than that for which they are rated. They 
must in all cases be provided with a name-plate, which shall 
be permanently attached beside the porcelain receptacle or 
receptacles, and stamped with the candle-power and voltage 
of the lamp or lamps to be used in each receptacle. 

c. Wherever insulated wire is used for connection be- 
tween resistances and the contact plate of a rheostat, the 
insulation must be slow burning. For large field rheostats 
and similar resistances, where the contact plates are not 
mounted upon them, the connecting wires may be run to- 
gether in groups so arranged that the maximum difference 
of potential between any two wires in a group shall not 
exceed 75 volts. Each group of wires must either be 
mounted on non-combustible, non-absorptive insulators giv- 
ing at least half -inch separation from surface wired over or, 
where it is necessary to protect the wires from mechanical 
injury or moisture, .be run in approved lined conduit or 
equivalent. 



Underwriters' Rules 1465 

5. Lightning Arresters, 

a. Must be attached to each wire of every overhead cir- 
cuit connected with the station. 

It is recommended to all electric light and power com- 
panies that arresters be connected at intervals over systems 
in such numbers and so located as to prevent ordinary dis- 
charges entering (over the wires) buildings connected to 
the lines. 

The kind and degree of protection necessary depend 
largely on circumstances. A short outdoor line from one 
mill building to another will often require nothings while 
a long overhead line through an open exposed country will 
generally need the most careful engineering to secure rea- 
sonable freedom from lightning disturbances. 

6. Must be located in readily accessible places away 
from combustible materials, and as near as practicable to 
the point where the wires enter the building. 

In all cases, kinks, coils and sharp bends in the wires 
between the arresters and the outdoor lines must be avoided 
as far as possible. - 

The switchboard does not necessarily afford the only loca- 
tion meeting these requirements. In fact, if the arresters 
can be located in a safe and accessible place away from the 
board, this should be done, for, in case the arrester should 
fail or be seriously damaged there would then be less chance 
of starting arcs on the board. 

The arresters should be accessibly located, so that they 
may be easily examined from time to time, and should al- 
ways be isolated from combustible materials, as sparks are 
sometimes produced when lightning is discharged through 
them. 

Kinks, coils, sharp bends, etc., may offer enormous re- 
sistance to a lightning current, possibly preventing its dis- 



1466 Steam Engineering 

charge to ground through the arrester and causing it to 
leave the wires at some other point, where it might do con- 
siderable damage. 

c. Must be connected with a thoroughly good and per- 
manent ground connection by metallic strips or wires hav- I 
ing a conductivity not less than that of a No. 6 B. & S. 
gauge copper wire, which must be run as nearly in a 
straight line as possible from the arresters to the ground 
connection. 

Ground wires for lightning arresters must not be attached 
to gas pipes within the buildings. 

It is often desirable to introduce a choke coil in circuit 
between the arresters and the dynamo. In no case should 
the ground wires from lightning arresters be put into iron 
pipes, as these would tend to impede the discharge. 

d. All choke coils or other attachments, inherent to the 
lightning protection equipment, shall have an insulation 
from the ground or other conductors equal at least to the 
insulation demanded at other points of the circuit in the 
station. 

6. Care and Attendance, 

a, A competent man must be kept on duty where gen- 
erators are operating. 

h. Oily waste must be kept in approved metal cans 
and removed daily. 

Approved waste cans shall be made of metal with legs 
raising can three inches from the floor, and with self-closing 
covers. 

7. Testing of Insulation Resistance, 
a. All circuits except such as are permanently grounded 

must be provided with reliable ground detectors. Detec- 
tors which indicate continuously, and give an instant and 
permanent indication of a ground are preferable. Ground 



Underwriters' Rules 1467 

wir€s from detectors must not be attached to gas pipes 
within the building. 

b. Where continuously indicating detectors are not feas- 
ible, the circuits should be tested at least once per day, and 
preferably oftener. 

c. Data obtained from all tests must be preserved for 
examination by the Inspection Department having juris- 
diction. 

These rules on testing to be applied at such places as 
may be designated by the Inspection Department having 
jurisdiction. 

8. Motors, 

The use of motors operating at a potential in excess of 
550 volts will only be approved when every practicable safe- 
guard has been provided. Plans for such installations 
should be submitted to the Inspection Department having 
jurisdiction before any work is begun. 

a. Must, when operating at a potential in excess of 550 
volts, have no exposed live metal parts, and have their base 
frames permanently and effectively grounded. 

Motors operating at a potential of 550 volts or less must 
be thoroughly insulated from the ground where feasible. 
Wooden base frames used for this purpose, and wooden 
floors, which are depended upon for insulation where, for 
any reason, it is necessary to omit the base frames, must 
be kept filled to prevent absorption of moisture, and must 
be kept clean and dry. Where frame insulation is im- 
practicable, the Inspection Department having jurisdic- 
tion may, in writing, permit its omission, in which case the 
frame must be permanently and effectively grounded. 

A high-potential machine should be surrounded with an 
insulated platform. This may be made of wood, mounted 
on insulating supports, and so arranged that a man must 



1468 Steam Engineering 

stand upon it in order to touch any part of the machine. 

In case of a machine having an insulated frame, if there 
is trouble from static electrcity due to belt friction, it 
should be overcome by placing near the belt a metallic 
comb connected to the earth, or by grounding the frame 
through a resistance of not less than 300,000 ohms. 

6. Motors operating at a potential of 550 volts or less 
must be wired with the same precautions as required for 
wires carrying a current of the same volume. 

Motors operating at a potential between 550 and 3,500 
volts must be wired with approved multiple conductor, 
metal sheathed cable in approved unlined metal conduit 
firmly secured in place. The metal sheath must be perma- 
nently and effectively grounded, and the installation of the 
conduit must conform to rules for interior conduits, ex- 
cept that at outlets approved outlet bushings shall be used. 

The motor leads or branch circuits must be designed to 
carry a current at least 25 per cent greater than that for 
which the motor is rated, in order to provide for the in- 
evitable occasional overloading of the motor and the in- 
creased current required in starting, without overfusing the 
wires; but where the wires under this rule would be over- 
fused, in order to provide for the starting current, as in 
the case of many of the alternating current motors, the 
wires must be of such size as to be properly protected by 
these larger fuses. 

The insulation of the several conductors for high poten- 
tial motors, where leaving the metal sheath at outlets must 
be thoroughly protected from moisture and mechanical in- 
jury. This may be accomplished by means of a pot head or 
some equivalent method. The conduit must be substantially 
bonded to the metal casings of all fittings and apparatus 
connected to the inside high tension circuit. It would be 



Underwriters' Rules ■> 1469 

much preferable to make the conduit system continuous 
throughout by connecting the conduit to fittings and motors 
by means of screw joints^ and this construction is strongly 
recommended wherever practicable. 

High potential motors should preferably be so located 
that the amount of inside wiring will be reduced to a mini- 
mum. 

Inspection Departments having jurisdiction may permit 
the wire for high potential motors to be installed accord- 
ing to the general rules for high potential systems when 
the outside wires directly enter a motor room. Under these 
conditions there would generally be but a few feet of wire 
inside the building and none outside the motor room. 

c. Each motor and resistance box must be protected by 
cut-out and controlled by a switch^ said switch plainly indi- 
cating whether ^"^on^^ or ^^off.^^ With motors of one-fourth 
horse-power or less on circuits where the voltage does not 
exceed 330^ single pole switches may be used. The switch 
and rheostat must be located within sight of the motor^ ex- 
cept in cases where special permission to locate them else- 
where is given, in writing, by the inspection department 
having jurisdiction. 

The use of circuit-breakers with motors is recommended, 
and may be required by the Inspection Department having 
jurisdiction. 

Where the circuit-breaking device on the motor-starting 
rheostat disconnects all wires of the circuit, the switch called 
for in this section may be omitted. 

Overload-release devices on motor-starting rheostats will 
not be considered to take the place of the cut-out required* 
by this section if they are inoperative during the starting 
of the motor. 



1470 ' Steam Engineering 

The switch is necessary for entirely disconnecting the 
motor when not in use, and the cut-out to protect the motor 
from excessive currents due to accidents or careless handling 
when starting. An automatic circuit-breaker disconnecting 
all wires of the circuit may, however, serve as both switch 
and cut-out. 

In general, motors should preferably have no exposed live 
parts. 

d. Eheostats must be so installed as to comply with 
all the requirements of Xo. 4. Auto starters must comply 
with requirements of No. 4c. 

Starting rheostats and auto starters, unless equipped with 
tight casings enclosing all current-carrying .parts, should 
be treated about the same as knife switches, and in all wet, 
dusty or linty places, should be enclosed in dust-tight, fire- 
proof cabinets. If a special motor room is provided, the 
starting apparatus and safety devices should be included 
within it. Where there is any liability of short circuits 
across their exposed live parts being caused by accidental 
contacts, they should either be enclosed in cabinets, or else 
a railing should be erected around them to keep unauthor- 
ized persons away from their immediate vicinity. 

e. Must not be run in series-multiple, or multiple-series, 
except on constant-potential systems, and then only by 
special permission of the Inspection Department having 
jurisdiction. 

The objection to combinations of this character is that 
the cutting-out of one motor, by accident or carelessness, 
may subject the others to a current or voltage greater than 
'that for which they are designed; and if this occurs, and 
the protecting devices fail, as sometimes happens, there is 
very likely to be severe arcing, or a burn-out. 



Underwriters^ Rules 1471 

/. Must be covered with a waterproof cover when not 
\n use^ and if deemed necessary by the Inspection Depart- 
ment having jurisdiction^ must be enclosed in an approved 
case. 

When it is necessary to locate a motor in the vicinity of 
combustibles or in wet or very dusty or dirty places, it is 
generally advisable to enclose it as above. 

Such enclosures should be readily accessible, dust proof 
and sufficiently ventilated to prevent an excessive rise of 
temperature. The sides should preferably be made largely 
of glass, so that the motor may be always plainly visible. 
This lessens the chance of its being neglected, and allows 
any derangement to be at once noticed. 

The use of enclosed type motor is recommended in dusty 
places, being preferable to wooden boxing. 

From the nature of the question the decision as to de- 
tails of constructon must be left to the Inspection Depart- 
ment having jurisdiction to determine in each instance. 

If possible, the enclosure should be large enough to per- 
mit the attendant to enter it and easily get at any part of 
the apparatus, and this would generally mean a small room. 
If the motor is suspended from the ceiling, a floor could 
generally be constructed below it and the four sides of this 
elevated motor room could be built mainly of windows. 
Eeady access to the room could be secured by means of a 
short flight of stairs or a ladder. This can also be done 
where the motor is supported on an elevated platform. 

With alternating-current motors having no brushes, the 
enclosure would generally be unnecessary. When located 
on the floor, it would often be advisable to surround the 
machine by a substantial pipe rail to keep pf^ople from 
passing near it. 



1472 Steam Engineering 

g. Must, when combined with ceiling fans, be hung 
from insulated hooks, or else there must be an insulator in- 
terposed between the motor and its support. 

h. Must each be provided with a name-piate, giving 
maker^s name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 

i. Terminal blocks when used on motors must be made 
of approved non-combustible, non-absorptive, insulating 
material such as slate, marble or porcelain. 

]. Variable speed motors, unless of special and appro- 
priate design, if controlled by means of field regulation, 
must be so arranged and connected that they cannot be 
started under weakened field. 

9. Railway Power Plants. 

a. Each feed wire before it leaves the station must be 
equipped with an approved automatic circuit-breaker or 
other device, which will immediately cut off the current 
in case of an accidental ground. This device must be 
mounted on a fireproof base, and in full view and reach of 
the attendant. 

An automatic circuit-breaker is preferable to a fu-se, as 
it acts more quickly, is more reliable, and can be more 
quickly and safely replaced. 

10. Storage or Primary Batteries, 

a. When the current for light and power is taken from 
primary or secondary batteries, the same general regula- 
tions must be observed as apply to similar apparatus fed 
from dynamo generators developing the same difference of 
potential. 

Charged storage batteries have in them at all times a 
large amount of stored energy, and should therefore be 
treated as carefully as generators of similar output. 



Underwriters' Rules 1473 

b. Storage battery rooms must be thoroughly venti- 
lated. 

The action of the current in charging the battery liberates 
at times large quantities of hydrogen and oxygen^ and if 
these should accumulate in the right proportions they would 
form an explosive mixture which might be exploded by any 
accidental spark. 

c. Special attention is directed to the rules for wiring 
in rooms where acid fumes exist. 

d. All secondary batteries must be mounted on non-ab- 
sorptive, non-combustible insulators, such as glass or thor- 
oughly vitrified and glazed porcelain. 

The battery needs to be insulated and nothing but glass, 
porcelain and similar materials will retain their insulating 
properties when exposed to the action of the water and 
acid freely used about storage batteries. 

e. The use of any metal liable to corrosion must be 
avoided in cell connections of secondary batteries. 

Eeduction of the cross-section of the connections by cor- 
rosion would probably cause them to be burned out by tho 
normal current of the battery. 

11. Transformers. 

a. In central or sub-stations, the transformers must be 
so placed that smoke from the burning out of the coil or 
the boiling over of the oil*(where oil filled cases are used) 
could do no harm. 

If the insulation in a transformer breaks down, consid- 
erable heat is likely to be developed. This would cause a 
dense smoke, which might be mistaken for a fire and result 
in water being thrown into the building, and a heavy loss 
thereby entailed. Moreover, with oil-cooled transformers, 



1474 Steam Engineering 

especially if the cases are JSlled too full^ the oil may become 
ignited and boil over, producing a very stubborn fire. 

&. In central or sub-stations casings of all transformers 
must be permanently and effectively grounded. 

Transformers used exclusively to supply current to 
switchboard instruments need not be grounded, provided 
they are thoroughly insulated. 

While from a fire standpoint it is not considered neces- 
sary to ground the casings of instrument transformers above 
mentioned, it is believed advisable to ground them in order 
to guard against danger from shock. It is evident that all 
other metal work such as switchboard frames, instrument 
cases, etc., which are liable to come in contact with a live 
circuit should also be grounded to protect against this dan- 
ger. 



^ Definitions 

A 

A. C. — Alternating Current. 

Absorption. — The act of one form of matter sucking, or 

draining in some other form of matter, as in the case 

of a sponge taking up water. 

Acceleration. — The increase of motion. 

Accumulated Electricity. — Electricity confined or stored, 

as in a condenser. 

Accumulator. — Sometimes used to designate a condenser, a 
Ley den jar, or a storage battery. 

Active Coil. — A coil or conductor conveying a current of 
electricity. 

Active Current. — The active constituent of an alternating 
current, in contradistinction from the wattless compo- 
nent. 

Active Wire. — The section of wire on the armature of a 
dynamo which goes through the field of force, in con- 
tradistinction from the remaining wire, which does not 
pass through the flux. 

Aerial Circuit. — An elevated circuit. 

Air Blast. — A blast of air acting upon the surface of a 
commutator to prevent damaging flashes. Also used to 
cool transformers in some cases. 

Air Gap. — Any gap or aperture in a circuit which con- 
tains air only. 

Air Insulation. — Insulation produced by the action of air. 

1475 



1476 Steam Engineering 

American Wire Gauge. — The name by which the Brown & 
Sharpe wire gauge is known^ in which the diameter of 
the largest wire^ No. 0000, is 0.46 inches, and wire No. 36, 
0.005 inches, and all other diameters progress in geomet- 
rical order. 

Ammeter. — An abbreviation for ampere meter. Used for 
measuring current rate, or volume. Any calibrated gal- 
vanometer having its scale marked to read amperes is 
an ammeter. 

Ampere. — The unit of electric current flow. An ampere is 
that volume of current which would pass through a cir- 
cuit that offered a resistance of one ohm under an electro- 
motive force of one volt. 

Ampere Hour. — A unit of quantity equal to the amount of 
electricity transmitted by one ampere flowing during one 
hour. 

Ampere Turn. — A unit of magneto-motive force equal to 
the force resulting from the passing of one ampere over a 
single turn of wire. 

Anode. — The positive pole a battery. 

Arc. — A segment of a circle. A voltaic arc. 

Armature Eeaction. — The reactive magnetic effect result- 
ing from the action of the current in the armature of a 
dynamo on the magnetic circuit of the machine. 

B 

B. S. G. — British standard gauge. 

B. & S. W. G. — Brown & Sharpe wire gauge. 

B. W. G. — Birmingham wire gauge. 

Balanced Load. — A load uniformly apportioned to two or 

more generators. 
Balanced Eesistance. — A resistance arranged in a bridge, 

and balanced by the residuary resistance in the bridge. 



Definitions 1477 

Bar Windings. — Armature windings constructed of copper 
bars. 

Bipolar. — Possessing two poles. 

Birmingham Wire Gauge. — A wire gauge used in England. 

Booster. — An auxiliary dynamo used to increase the volt- 
age of a feeder^ or a set of feeders beyond the voltage of 
the rest of the system. 

Bridge, Electric. — A contrivance used to measure unknown 
resistances by comparison with adjustable ones. 

Bunched Cable. — A cable having more than one wire, or 
conductor. 

Bus-bars. — Bars composed of heavy conducting .metal, and 
connected directly with the poles of generators. 

C 

C. G. S. — Centimetre, Gramme, second. 

C. P. — Candle power. 

Calibrate. — To ascertain the complete or relative values of 
the indications of electrical measuring instruments. 

Candle. — The unit of photometric energy. Equals the light 
produced by a standard candle burning at the rate of two 
grains per minute. 

Cathode. — Opposed to. anode. 

Condenser. — A device for augmenting the capacity of an 
insulated conductor by placing it in contiguity to another 
earth-connected conductor, but from which it is sep- 
arated by an intervening body which will permit electro- 
static induction to occur through it. 

Constant Current. — A current, the strength of which does 
not vary. 

Continuous Current. — A current flowing in the same di- 
rection only. 

Cycle of Alternations. — Alternations of the current per 

second. 



1478 Steam Engineering 

Coulomb. — The unit of electric quantity accepted for prac- 
tice. That quantity of electricity that would pass in one 
second through a circuit conveying one ampere. That 
quantity of electricity contained in a condenser of one 
Farad capacity when subjected to an E. M, P. of one 
volt. 

D. 

D. C. — Direct current. 

D. P. S. — Double pole switch. 

DiflEerential Winding. — Double winding of magnet coils 
resulting in the opposition of the two poles to each other. 

Dynamic Electricity. — Current electricity as distinguished 
from static electricity. 

Dyne.— The C. G. S. unit of force. 

E 

E. H. P. — Electrical horse-power. 
E. M. P. — Electromotive force. 

Electrolysis. — Chemical decomposition by the action of an 
electric current. 

F 

Farad. — The practical unit of electrical capacity. That 
capacity of a conductor that is capable of holding one 
coulomb at one volt potential. 

Feeders. — Wires furnishing the main conductors with cur- 
rents at different points^, thus serving to equalize the po- 
tential under load. 

Five- wire System. — A system wherein four series connected 
dynamos are connected to five conductors. 

Flux. — Magnetic induction; the number of lines of force 
which pass through a magnetic circuit. 

Frequency. — Number of cycles per unit of time by an al- 
ternating current. 



Definitions 1479 

G 

Gramme. — A unit of weight equal to the weight of one cubic 
centimetre of pure water at its maximum density, at a 
temperature of 39.2° Fahr. in a vacuum. A weight 
equal to 15.44 grains troy. 

H 

H. P. — Horse-power. 

Hard-drawn Copper Wire. — Copper wire hardened without 
annealing, by being drawn several times. 

Henry. — The practical unit of electro-magnetic, or mag- 
netic inductance. 

Horse-power, Electric. — A rate of electrical work "equal to 
746 watts, or 746 volt-coulombs per second. 

Hysteresis. — Slowness of magnetization in respect to mag- 
netizing force. 

I 

Induction. — The influence exerted without contact, by a 

magnetic field, or a charged mass upon neighboring 

bodies. 
Inverted Arc Lamp. — An arc lamp wherein the positive 

carbon is below instead of above, as in the regular arc 

lamp. 

J 

Jump Spark.— A disruptive spark excited between two con- 
ductors, in distinction from a spark excited by a rubbing 
contact. 

K 

K. W.— Kilowatt. 
Kilowatt. — One thousand watts. 

Kilowatt-Hour. — Work equal to the expenditure of one K. 
W. in one hour. 



1480 Steam Engineering 

L 

Lag. — Dropping behind. 

Lagging of Current. — The retarding in phase of an al- 
ternating current behind the pressure which produces it. 

M 

Megohm. — One million ohms. 

Metre. — A measure of length equal to 39.368 inches. 

Micro-Fard. — The millionth of a Farad. 

Mil. — One thousandth of an inch. 

Multiphase. — Containing more than one phase. 

Multiple Circuit. — A circuit in which the positive poles of 
a number of separate sources^ and receptive devices are 
connected to a single positive lead or conductor; their 
negative poles being connected to a single negative lead 
or conductor. 

Multiple Series. — Series groups connected in multiple. 



Ohm. — The practical unit of resistance. A resistance that 
would confine the electric flow under an electromotive 
force of one volt to a current of one ampere, or one cou- 
lomb per second. 

Ohm's Law. — The basic law, expressing the relation be- 
tween current, E. M. F., and resistance in active cir- 

E 
cuits. Expressed algebraically I^ — ^ in which I equals 

E 

current intensity, E equals E. M. F., and E equals resist- 
ance. Other forms of expressing ohms law are as follows : 

E 
E=:— . E=EI. 

I 



Definitions 1481 

Over Compounded. — Compound winding of such a charac- 
ter on a dynamo that its voltage at its terminals is caused 
to increase under a greater load. 

P 

Parallel Circuit. — A term signifying multiple circuit. 

Parallel Series. — Signifies a multiple series connection. 

Periodicity of Alternation. — The rate of successioM of al- 
ternations per second^ or per minute. The frequency. 

Polyphase Current. — Currents that constantly differ from 
each other, due to their proportion of periods of alter- 
nation, and adapted to polyphase motors. 

Proposed Definition for 2,000 Candle Power. — An arc 
whose maintenance will require 450 watts. 

E 

Eheostat. — Will adjust the resistance without opening the 
circuit. 

S 

Standard Ohm. — A piece of pure copper wire one circular 
mil in diameter, and one foot long at a certain tempera- 
ture. 

Static Electricity. — Electricity generated by friction. 

V 

Volt. — The practical unit of electromotive force. An E. 
M. F. that would cause a current of one ampere to flow 
through a resistance of one ohm. 

W 

Water Horse-Power. — The power developed by 15 cubic feet 
of water falling through a distance of one foot per second. 

Watt. — The practical unit of electric activity, rate of work, 
or energy. A watt equals 44.25 foot pounds of work done 
per minute, or 0.7375 foot-pounds of work done per sec- 
ond. 

Watt-Hour. — Unit of electric work. One watt exerted or 
expended for one hour. 



Ind 



ex 

A 

Page 

Table — Areas and circumferences of circles 361-363 

Table — Areas of segments of circles 113-114 

Table — Areas of segments for boiler bracing 86 

B 
Table — Boiling point of water at various altitudes 302 

C 

Table — Carrying capacity of armature wires at various depths 

of winding, and 3 sq. in. of radiating surface per watt 1198 

Table — Carrying capacity of armature wires at various depths 

of winding, and i sq. in. of radiating surface per watt. .... .1199 

Table — Carrying capacity of pure copper wire 1381 

Table — Columns and I-beams for boiler setting 64-65 

Table — Commercial power gases — general properties 7x6 

Table — Comparison of thermometer scales 290 

Table- — Composition of various coals .^ 284 

Table — Constituents of power gases 'J^y 

Table — Contents of cylinder in cu. ft. for each lineal foot in 

length 825 

Table — Cubic feet of ammonia gas required per minute per ton 

of refrigeration 899 

D 

Table — Diameters of boiler rivets 89 

Table — Diameter and pitch of rivets — double riveting 90 

Table — Dimensions of pure copper wire.* 1382 



Index 

E 

Table — Efiiiciency of incandescent lamps 1428 

Table — Efficiencies of air compressors at various altitudes. . . . 826 

F 

Table — Factors of evaporation , 343 

Table — Flow of air through openings of various diameters.827-828 

Table — Flow of steam through pipes 311 

Table — Friction tests .....; 559 

H 

Table — Horse-power required to compress air 825 

Table — Hyperbolic logarithms • • • • 454 

J 
Table — Joint efficiencies (boiler) 91 

K 
Table — Kindling temperatures 283 

L 

Table — Lap and lead of Corliss valves ^ 402 

Table — Lloyd's rules 90 

Table — Loss of heat from steam pipes 309 

Table — Loss of pressure through friction of air in pipes 829 

M 
Table — Mean effective pressures 830 

N 

Table — Number of expansions 367 

Table — Numbers : their square roots and cube roots 366 

O 
Table — Otis electric elevator data 942 



Index 



P 



Table — Packing tests 558 

Table — Physical properties of saturated steam 278-282 

Table — Pressure of water 181-182 

Table — Properties of saturated ammonia 918-919 

Table — Proportions and efficiencies of riveted joints 90 

Table — Proportions of single and double riveted joints 91 

Table — Proportions of single riveted lap joints 92 

Table — Proportions of double riveted lap and butt joints 93 

Table — Proportions of triple riveted butt joints 94 

Q 

Table — Quantity of injection water required for jet condenser 2)^$ 

R 

Table — Relative value of non-conducting materials 307 

Table — Requirements of pneumatic drills at various altitudes. . 831 

S 

Table — Sizes of air pumps — single acting 364 

Table — Sizes of chimneys with appropriate horse power of 

boilers 22,7 

Table — Sizes, weight and resistance of pure copper wire 1386 

Table — Spacing multi-gap lightning arresters 1338 

Table — Specific heat of various substances. . . .• 295 

T 

Table — Theoretical draft pressure in inches of water, in a 
chimney 100 feet high 236 

V 

Table — Volume of air required for rock drills at sea level. . . . 831 
Table — Volume and weight of air at various temperatures, and 
at atmospheric pressure 24a 



Index 

W 

Table — Weight of one cubic foot of water 301 

Table — Wiring table for 1 10 volts . . * 1383 

Table — Wiring table for 220 volts 1384 

Table — Wiring table for 500 volts 1385 

A 

Absolute zero 448 

Adiabatic curve .449, 536-538 

Air, composition of 238-239 

Weight and volume of 239-240 

Air compression 811-853 

Adiabatic 812 

At high altitudes 826 

Catechism on 849-853 

Compound compression 816-824 

Conditions necessary for 811 

Flow of free air through an orifice 827-828 

Inter-cooling 816 

Isothermal 812 

Jacket cooling 816 

■ Loss of pressure through friction. . . .829-830 

Mean effective pressures 830 

Methods of removing heat of compression 814-819 

Multi-stage 816-820 

Sources of loss in 811 

Volumetric efficiency 821-822 

Air Compressors 811-853 

Allis-Chalmers ^ 845-849 

Dallett 843-845 

Ingersoll-Rand 833-842 

Compound 816 

CyHnder lubrication .' 823-824 

Drier air 822-823 

Installation 831-833 

Multi-stage 816-824 

Pipe connections 832-833 



Index 

Reduced strains 819-820 

Single stage 822-823 

Steam economy 820 

Three stage 819 

Two stage 819 

Usefulness of 812 

Allis-Chalmers Air Compressors 845-849 

Discharge valves 845 

Rotary inlet valves 845 

Valve gear 846-849 

Allis-Chalmers Gas Engine 764-770 

Design and construction of 766-767 

Igniters 769 

Lubrication 769-770 

Valve gear of 768 

Allis-Chalmers Steam Turbine 649-662 

Action of steam in 652-653 

Balance pistons 652-653 

Bearings 655 

Blades 653, 654-656 

Description of 649-651 

General view of 650 

Governor 655 

Starting and operating 658-662 

Thrust bearing 653 

Aluminum Lightning Arrester 1352-1358 

600 volt D. C .1324 

Condenser action 1354 

Design 1356-1358 

Film dissolution 1354 

For 1 10,000 volts 1356 

Valve action 1352 

American Stoker* 214-216 

American-Thompson Indicator 468-470 

Ammonia ' 916-920 

Anhydrous, composition of 859 

Composition of ; 916 

Danger in fumes 911-912 

How obtained 917 



''Z Index 

Hydrometer 920 

Properties of 918-919 

Specific gravity 917 

Testing 919-920 

Ammonia Condenser — Double Pipe 890-896 

Brine system • 892-895 

Direct expansion system 895-896 

Angular Advance , 456-457 

Arc Lamps 1406 

Action explained 1406 

Adjusting weight 1409 

Brush lamp 1409-1414 

Burning upside down 1407-1408 

Carbons 1413-1414, 1424 

Heat of arc 1408 

Mechanism 1408 

Method of suspension 141 1 

Armature 1151-1191 

Balancing 1151-1153 

Bearings and pole pieces 1154-1155 

Centering 1153-1154 

Compensation for losses 1151 

Materials to be used .1155-1156 

Mechanical construction 1155-1159 

Punched discs 1155-1158 

Slotted ,.... 1156-1158' 

Armature Winding 1 158-1224 

Advantages of drum style. . 1161-1162 

Catechism on 1 192-1224 

Compared with ring winding 1 164 

Connections for 8 coils 1167-1168 

Connections for 12 coils 1173-1175 

Dead wire in 1 160 

Development of 1170-1173 

Drum windings 1 164-1 191 

Formulae for spacing 1168-1169 

Gramme ring 1159-1164 

Insulating materials 1 185-1 186 

Lap winding 1180-1181 



Index 

Multipolar windings 1 176-1 185 

Simplicity of 1 165-1 168 

Wave winding 1181-1185 

Winding table 1169-1170, 1173, 1185 

Various methods of applying the wire 1185-1191 

Armington and Sims Shaft Governor.- • ". . .435-438 

Atlas Shaft Governor 433-435 

Atlas Water Tube Boiler 38-48 

Design and construction 38-42 

Method of feeding 43-46 

Safe working pressure 40 

Automatic Furnaces — Murphy 207-209 

Automatic Furnaces — Burke 220-223 

B 

!Babcock & Wilcox Boiler 16-21 

Construction of steam drums 18 

End connections for tubes 16-18 

Erection 18 

Method of connecting 16-18 

Operation 18-21 

^ack Arches 124-127 

Barnes Draft Gauge 332-334 

batteries — Primary 1429-1454 

•Batteries — Storage 1447-1454 

Belpaire Boiler 106-107 

Calculating strength of stayed surfaces ....111-116 

Dished heads 117 

Strength of unstayed surfaces 116-117 

Through stay rods 108-1 1 1 

Welded seams 118 

iBigelow-Hornsby Boiler 30-34 

Admission of feed water 32-33 

Largeness of units 32 

Section through setting 31 

Blow-off Pipes . . . , • 144-145 

JBoilers, care and operation of 262-277 

Blisters and cracks ^63 



Index 

Blowing off 264 

Catechism on 270-277 

Feed pump or injector 262 

Fusible plugs 263 

Gauge cocks and water glasses 262 

Loss in handling coal 269-270 

Miscellaneous matters 265-270 

Boiler Construction 77-122 

Bursting pressure illustrated 83 

Bursting pressure, formulae for finding 84-85 

Bracing, rules and tables for .85-88 

Catechism on 1 18-122 

Crowfoot brace 103-104 

Gusset stays and stay bolts 104-108 

Importance of safe construction 77-78 

Materials for 78-79 

Punched and drilled plates 79-80 

Riveting, rules for .81-83 

Rivets, diameters of 89 

Riveted joints, proportions and efficiencies. 90-93 

Single riveted lap 94-95 

Double riveted butt : .95-97 

Triple riveted butt 97-98 

Quadruple riveted butt ^. ... .98-102 

Weakest parts of .90-102 

Safe working pressure 85 

Staying flat surfaces 102-1 16 

Boiler Horse Power 345 

Boiler Setting and Equipment 123-244 

Back arches 124-127 

Blow-off Pipes 144-145 

Catechism on 182-188 

Domes and mud drums 143 

Feed pipes 145-147 

Feed pumps * 148-158 

Selection of 148-149 

Feed pumps, the Prescott 152-154 

The Worthington 15S-156 

Care and operation I57-I59 



Index 

Fusible plugs 142, 143, 263 

Grate surface • , 128 

Insulation 129 

Methods of support , 123-124 

Provisions for testing 159-162 

Safety valves 135-142 

Rules for 140-142 

Setting steam valves of duplex pumps 150-152 

Steam headers and connections 170-173 

Steam gauges ♦. 132-134 

Steam superheaters 173-176 

The injector ! 163-170 

Principles governing its actions 163-168 

Sellers improved 168-170 

Water columns 130-132 

British Thermal Unit (B. T. U.) : .293, 294, 298 

Brush Arc Dynamo 1087-1098 

Automatic regulation 1092-1093 

Care of commutator 1091 

Connections of 1088-1089 

Controller 1093-1096 

Setting the brushes 1089-1091 

Starting 1096-1098 

C 

Catechism on Air Compressors 849-853 

Armature troubles 12201225 

Armature winding 1 192-1224 

Boilers 66-75 

Boiler construction 1 18-122 

Care and operation of boilers 270-277 

Combustion, heat and water 313-316 

Definitions 458-461 

Electricity . . .' 1124-1135 

Electric currents 1 148-1 151 

Elevators 1012-1018 

Evaporation tests 346-349 

Gas engines 803-810 



Index 

Indicator work 548-550 

Lubrication and friction S77-S79 

Mechanical draft 241-243 

Refrigeration 921-928 

Rotary converters 1291-1295 

Steam engines 368-371 

Steam turbines 703-710 

Switchboards 1358-1364 

Transformers 1289-1291 

Valve setting 438-444 

Cahall Water Tube Boiler. 3-8 

Construction of 4-7 

Swinging man-head 4-5 

Tubes 7 

Calculation of Wires ♦ 1373 

Calorimeter 323-324, 329 

Calorific value of fuel 286-287 

Carbon 284 

Care and Operation of Boilers 245-270 

Ash conveyor 247-250 

Cleaning fires 245-246 

Duties of engineer 245 

Feed water 259, 264 

Fire tools 246-247 

Firing— rules for 253-255, 263 

Foaming and priming 260-261, 264 

Pressure gauge 261-262 

Renewing tubes o 257-259 

Safety valves 261 

Washing out and cleaning 256-257, 263 

Water level 262 

Chimneys 231-240 

Dimensions of 22,^22,6 

Functions of 231 

Iron 237-238 

Rules and Formulae for 233-238 

Types of 222-22Z 

Clearance 448 



Index 

Combustion 282, 288-336 

Calorific value of fuel 286-287 

Carbon 284 . 

Coal — Analysis of 284-285 [ 

Hydrogen — Heating value of ' 284 

Kindling point 283 

Nitrogen 286 

Oxygen, necessary for 283, 335-336 

Temperature of the furnace 287 

Compound Engines 351-352 

Condensers 352-364 

Jet 352-356 

Siphon 358 

Surface 357-364 

Condensers for Steam Turbines 697 

Consolidated Ice Machine 880-890 

Construction of piston. 883 

Copper water jacket 882-883 

Detailed description of 880-881 

Stuffing boxes 883-884, 888-890 

Suction and discharge valves 882-886 

Coxe Mechanical Stoker 203 

Crosby Indicator 465, 471-476 

Current Distribution 1365-1373 

Center of distribution 1372 

Divided circuits 1365-1367 

Feeders 1372 

Multiple series 1369-1379 

Service wires : 1372 

Series multiple 1369-1379 

Three wire system 1370-1373, 1379 

With two dynamos 1399-1405 

Three wire parallel system 1368-1369 

Wiring systems 1367 

Curtis Steam. Turbine .611-632 

Action of steam in 617-618 

Admission valves 617 

Baffler 632 

Clearance 629-630 ! 



Index 

Governor 622-626 

Initial nozzles and buckets 612-616 

Shaft 613 

Speed regulation 618-622 

Step bearing , 629 

'*■ Wheels and stages 614-617 

Cylindrical Flue Boiler I 

D 

i Dallett Air Compressor 843-845 

General description of 843 

Governor and safety stop 843-8/14 

Inlet and discharge valves 845 

Definitions — Electric , 1475-1481 

\ Definitions 445-458 

Of absolute zero 448 

Angular advance — lap and lead 456-457 

Clearance 448 

Efficiency of plant 450-452 

Expansions 446-447 

Horse-power 448 

Logarithms 452-454 

Motion, force, work .449-450 

Pressures 445-446 

Vacuum 447-448 

Catechism on 458-461 

Deitz High Pressure Lubricator 574-576 

De Lavergne Refrigerator , 872 

Action of machine explained 874-878 

Characteristic features of 872-873 

Sealed stuffing box 873 

De Laval Steam Turbine ^?i2>-(>ZA 

Action of steam in .640-642 

Description of parts 636-640 

Efficiency tests of 646-647 

Gear — Flexible shaft 642-643 

Governor 644-645 

High speed of • 6z3-^2i^ 



Index XV 

Nozzles 634 

Wheel 647 

Detroit Lubricator 566-570 

Diagram Analysis 485-550 

Adiabatic curve 449, 536-538 

Catechism on indicator work 548-550 

Criticism of various diagrams 486-490 

Explanation of a diagram 485-486 

Isothermal curve 449 

M. E. P., how to ascertain 490-493, 510-512, 516-520, 545 

Ordinates, how to draw 539-543 

Power calculations 539-548 

Power test diagrams 506-510 

Rule for strength of spring 497 

Showing spring to be too strong. . .- 494-495 

Steam consumption from 521-527 

Theoretical clearance 527-531 

Theoretical expansion curve 449, 531-536 

Unequal cutoff 495-498 

Wire drawing of steam 499 

Diagrams from Gas Engines 744-749 

Disposal of Exhaust of Steam Turbines 697-703 

Condensers for steam turbines ,.•.•• 697 

Catechism on steam turbines 703-710 

Dry air pump 698-699 

Efficiency of turbine or reciprocating engine 699-701 

Surface condenser, action of .701-703 

Domes and Mud Drums , 143 

Dry Air Pump 698-699 

Duplex Steam Pumps .150-152 

Duplex Water Tube Boiler 51-56 

Method of Support 54 

Sectional view of 52 

Strong features of 51 

Water circulation in 55 

D. Slide Valve Z7Z-377 

Action of * 375-379 

Du Bois Tandem Gas Engine 779-788 

Characteristic features of 779-782 

Ignition 785-786 



'^ . Index 

Lubrication 7^7 

Mixing valve 784-785 

Starting 787-788 

Valves, valve gear and governor ... .782-785 

Dynamo 1084-1123 

Brush arc ICS7-1098 

Constant current, operation of 1084-1087 

Thomson-Houston 1098-1 109 

Dynamo— Electric Generators 1033-1072 

Alternator 1036-1139 

Brush holders ic6i 

Brushes and commutators .1058-1065 

Carbon brushes 1059-1060 

Classification of 1033-1034 

Commutator 1041-1043, 1058 

Compound dynamo 1069-1070 

Constant potential dynamos 1073 

D. C. generator . , 1039-1046 

Drum windings 1046, 1053-1055 

Function of 1033 

Generation of current 1034-1036 

General rules for starting 1081-1082 

Gramme ring 1047-1052 

Operation of 1073 

Over-compounding 1070-1072 

Principal parts of 1034 

Regulation 1057-1058 

Rheostat 1074-1075 

Self-excitation 1055-1056 

Series dynamo 1068-1069 

Shunt dynamo 1069 

Short circuit 1077 

Starting machines . 1078-1082 

Under-compounding 1072-1073 

Dynamo Troubles 1387-1396 

Bearings, wear of 1394 

Brushes and commutator 1392-1396 

Care in operation 1387-1389 

Motor compensator for three wire 1401-1405 



Index 

Lubricators I393-I395 

Sources of trouble 1388-1391 

Sparking), causes of 1391-1392 

Startiiig a new generator 1401-1405 

E 

Efficiency of Plant 339, 450-452 

Electricity 1019-1481 

Ampere turns 1032 

Conservation of energy 1019-1020 

Coulomb 1022 

Current may be measured 1019 

Electro-motive force 1031-1033 

Extent of knowledge regarding it 1019 

Foucault currents 1032 

How measured 1021-1023 

Induction — Faraday's law of 1032 

Ohm 1022 

One form of energy 1020-1021 

Volt 1021-1022 

Volt-Coulomb or Joule 1022 

Watt 1022-1023 

Electric Currents 1137-1147 

Alternating current (A. C.) 1137-1143 

Catechism on 1148-1150 

Current waves 1 140-1 142 

Delta winding 1 146 

Direct Current (D. C.) 1137-1143 

Frequency — Alternations 1141 

Maximum voltage 1 141-1 142 

Phase, lag and lead 1143-1145 

Polyphase 1 147 

Two and three phase 1 145-1 146 

Waves in quadrature 1 147 

Waves in opposition 1 147 

Y. Winding 1 14,6-1 147 

Electric Elevators 1009-1018 

Boiler power required for 1009-1012 



Index 

Catechism on 1012-1018 

Electric Motors 1 109-1 124 

Action explained 1 109-1 1 1 1 

Alternating current motors .' 1118-1119 

Catechism on 1 124-1 135 

Compound wound 1116-1117 

Construction of mo 

Course of current in , 11 13 

Electro-motive force of 1 1 1 i-i 1 12 

Faults of 1 1 18 

Highest speed of 1112-1114 

Induction motor 1121-1123 

Series wound .1115-1116 

Starting box 1117-1118 

Synchronous motors 1121-1123 

Electro-Meters 1303-1319 

Ammeters and volt-meters 1304 

Galvanometers 1303-1304 

Volt meter 1310-1314 

Watt meters 1314-1317 

Weston instrument 1304-1310 

Electro-magnetic induction 1030-103 1 

Elevators 929-1018 

Morse-Williams 979-985 

Otis traction — electric .929-931 

Otis hydraulic 944-971 

Whittier hydraulic , 975-979 

Ellison's Draft Gauge 334-335 

Erie City Water Tube Boiler 56-60 

Side elevation of 58 

Spacing of tubes 57-58 

Steam separation 59-60 

Evaporation Tests 317-345 

Apparatus necessary 318-320 

Barrus draft gauge 33^-3ZA 

Boiler horse-power 345 

Calorimeter 323, 324-329 

Catechism on 346-349 

Conducting a test 318-325 



Index 

Determining quality of the steam 322-331 

Ellison's draft gauge 334-335 

Efficiency of plant — calculation of .339-340 

Efficiency of boiler — calculation of .340-341 

Equivalent evaporation explained .342-343 

Factors of evaporation 343 

Flue gas analysis 3ZS-ZZ9 

Measuring chimney draft 33^-2>2>S 

Object of 317 

Orsat apparatus ZZ^-3Z9 

Preparing for 317-318 

Expansion 446-447 

F 

Factors of Evaporation 343 

Feed Pipes 145-147 

Feed Pumps 148-158 

Feed Water for Boilers 259-264 

Feed Water Heaters 189-197 

Hoppes, class R I93-I97 

Kinds of 190 

Open, or closed 190-195 

Saving effected by 190-193 

Field of Force 1028-1029 

Fitchburg Engine 419-428 

Adjusting valves of 425-428 

Type of valves 420-423 

Flow of Steam Through Pipes 310-313 

Flue Gas Analysis 335-339 

Foot Pound 293-294 

Force 449-450 

Friction — Laws of " 551-555 

Co-efficient of 553-555 

Kinds of in mechanics 553 

Of piston rod packing 557-560 

Second law of, illustrated 553-554 

Fusible Plugs 142-143, 263 



»~^ Index 

G 

Gas Engine 711-810 

Advantages of 750-751 

Back pressure in .^ 747 

Batteries for ignition spark 722-724 

Catechism on 803-810 

Combustion for 718-746 

Compared to steam engine 711-712 

; Compression in 719-720, 748 

^ Cylinder lubrication 803 

Diagrams from 744-749 

Efficiency of power gases 736 

Economy of 749-750 

Exhaust of 730-733 

Explosion and expansion 730 

Explosive mixture .728-730 

Finding centers 72>2>-7ZA 

Fuel for , 714-717 

Indicator — Crosby, new 738-739 

Crosby with detent * 739-741 

Tabor outside spring. 742-743 

Ignition — Magnetic y26 

Timing of y2y 

Various methods of .719-728 

I. H. P., calculations of .748-749 

Induction of charge . 718 

Lubrication of 802-803 

Producer gas ; 751-753 

Spark coils 726-728 

Valve setting 72>3-7?>^ 

Valve timing ,. 733 

Allis-Chalmers 764-770 

Du Bois 779-788 

Reeves 792-795 

Snow 77^-779 

Tower 788-792 

Westinghouse 77o-yy6 

Gasoline Engine 795-801 

Carbureter 797-798 



Index 

Constant level overflow 797 

Gasoline pump 796 

Generator or mixer 800-801 

Principles governing action 795-798 

Gas Producer 753-764 

Efficiency of 763-764 

Hydrogen content 764 

Induced down draft 762-763 

Regulation of 764 

Steam pressure type 7^1-762 

Suction type 753-762 

Gramme ring 1047-1052 

Grate surface 128 

Greene-Wheelock engine 411-420 

Description of valves 412-414 

Setting valves of 415-419 

H 

Hamilton Holzwarth Steam Turbine 663-679 

Action of steam in 673-674 

Catechism on 703-710 

Clearance of blades 666-668 

Comparison with other types 665-666 

Construction of blades .668-669 

Governor — Regulation 675-677 

Running wheels ^ 669-673 

Stationary discs 674-675 

Stuffing box 677-679 

Heat 288-298 

Absolute zero 290-291 

British thermal unit (B. T. U.) 293, 294-298 

Dr. Joule's discovery 292-293 

Effects of 290 

Foot pound 293-294 

Nature of 288-291 

Sensible and latent heat . ; 295-297 

Specific heat .294-295 

Thermo-Dynamics — First law of 292 



Index 

Total heat of evaporation 298 

Work done by .297-298 

Heating Surface 266-269 

Horse-power Explained 518-520 

Hoppes Feed Water Heater I93-I97 

Hydraulics for Engineers 176-180 

Hydraulic Elevators 944-1012 

Action explained 944-946 

Boiler power required for 1006-1009 

Construction of 946-947 

Counterbalance 965 

Cylinders — Arrangement of 964 

Horizontal cylinder 973-985 

Operating devices 965-973 

Operating valve -954-959 

Piston and piston packing 962-963 

Pressure tank '957-958 

Safety governor, Otis 951-954 

Speed limit devices 947-951 

Throttle valve 959, 962-971 

Vertical cylinder 960-973 

Hydrogen 284 

I 

Ice Making 896-899 

Requirements for pure ice 897 

Process explained 997-998 

Incandescent Lamp 1425-1429 

Action explained 1425 

Current required for 1426-1427 

Efficiency of 1427-1429 

Resistance 1426 

Selection of 1426 

Incrustation in Boilers 299-300 

Indicator, the 463-485 

Adjustment of valves with 499-502, 503-506 

American-Thompson 468-470 

Attaching to cylinder 481-482 



Index ^..^-\ 

Care of .482-483 

Causes of error ; . . , .512-516 

,, ' Crosby .465, 471-476 

How to take diagrams 483-485 

Invention of , . , 463 

Principles of its action 463-465 

Reducing mechanism 470, 476-480 

Tabor .467-468 

Indicators for Gas Engines 736-749 

Crosby, new 72>^-7Z9 

Crosby with detent 739-741 

Monagraph for high speed y42>-7AA 

Tabor outside spring 742 

Tabor parallel motion 742-743 

Ingersoll-Rand Air Compressor .833-842 

Air ball governor , 838-839 

Internal construction 833 

Mason governor 840-842 

Meyer cut-off valve .834-840 

To remove inlet valves .836-837 

To set cut-off eccentric 837-838 

To start 842 

Unloader and regulator 834-836 

Injector, the 163-170 

Isothermal Curve 449 

J 

Jones underfeed Stoker .216-219 

K 
Kindling Point 283 

L 

Lap — Inside 374 

Lap— Outside 374-375, 388 

Latent Heat 295-297 

Lead 374 



Index 

Lightning Arresters .*. 1319-1364 

Aluminum — 600 volt D. C 1324, 1352-1358 

Catechism on » 1358-1364 

Choke coils .1345-1347 

Connections • • ^Z^^ 

Constant current arresters 1344 

D. C. arresters '. 1347-1349 

Discharge of lightning ... 1319 

Disconnecting switches 1344-1345 

Distribution of stress 1328 

Fuse auxiliaries 1337-1338 

Ground connections 1349-1352 

Horn gap installation 1350 

Inspection • 1326-1328 

Low voltage arresters 1339-1342 

Multigap arresters 1321-1322 

Oscilliograph curves 1341 

Protection of cable systems 1342-1344 

Protection of electric circuits 1320 

Resistance in arrester 1322-1324 

Sparking of gaps 1329-1330 

Voltage range 1339 

Linde Ice Machine 863-872 

Action of .863-868 

Indicator diagrams from 865^-866 

Stuffing box 869-871 

Logarithms 452-454 

Lubrication 550-579 

Catechism on 577-579 

Cost of 561 

Graphite as a lubricant 562-564 

Of interior surfaces 564-565 

Requirements of a good lubricant 560-561 

Lubricating Appliances 565-577 

Detroit lubricator 566-570 

Dietz high pressure device 574*576 

Manzel oil pump 574 

Powell lubricator 570-574 

Rochester force feed 576-577 



Index 

M 

Magnets 1023-1031 

Charging — various methods of 1024 

Direction of current 1026-1027 

Electro-magnet 1024 

Electro-magnetic induction 1030-1031 

Field of force 1028-1029 

Lines of force 1024, 1027-1031 

Natural magnet 1023 

Permanent magnet 1023-1024 

U-shaped magnet 1024 

Mansfield Chain Grate Stoker 201-202 

Marzolf Boiler 48-51 

Admission of feed water 51 

Baffle and path of gases 50-51 

Sectional view of 49 

Maxim Boiler 28-30 

Arrangement of heating surface 30 

Front elevation 28 

Mechanical Draft 223-243 

Catechism on 241-243 

General forms of apparatus 22^-2^1 

Mechanical Stokers 197-223 

American under-feed 214-216 

Classes of 200-201 

Coxe 203 

Jones under-feed , .216-219 

Mansfield chain grate 201-202 

Playford 202-204 

Roney 209-213 

Vicars 204 

Wilkinson 205-207 

M. E. P. — How to Ascertain 490, 510, 545 

Mil — Circular and Square I373-I379 

Monahan Gas Producer 756-758 

Morse- Williams Hydraulic Elevator 979-985 

Double-decked machiile 979-981 

Operation 983-985 



Index 

Motion 449-450 

Murphy Furnace 207-209 

N 
Nitrogen 286 

O 

Oil Engines 8ioa-8ioi 

Switches 1297-1303 

Principles of construction 1297-1298 

Safety of 1299 

Westinghouse — types B and E 1300-1303 

Westinghouse — type I 1298, 1300-1301 

Ordinates — How to Draw Them 539-543 

Orsat draft Gauge .336-339 

Oscilliograph Curves , 1341 

Otis Direct Acting Hydraulic Elevators 997-1006 

Construction of cylinder 1002-1006 

Installation 999-1000 

Stuffing box 1005 

Otis High Pressure Elevators — Hydraulic 985-997 

Accumulator 988-989 

Advantages of .985-986 

Arrangement of parts 986-989 

Cylinder and plunger 993-995 

Main and pilot valves 992-993 

Movement of water in 989-992 

Otis Traction Elevator — Electric 929-944 

A. C. Machines 936-937 

Arrangement of cables 930-931 

Brake 936 

Controller 931-932 

Geared traction machines 933-938 

Lever car switch 939 

Magnet controller 938 

Motor — description of 929-930 

Oil cushion buffer 932-933 

Operating — suggestions for 940-944 

Oxygen 283, 335-336 



Index 

P . / 

Pressure-bursting 83-85 

Safe working 85 

Pressure gauge 261-262 

Pressures 445-446 

Primary batteries 1429-1454 

Action of 1430-1431 

Carbon cylinder cell 1431-1432 

Care of 1437-1442 

Closed circuit 1431 

Dry batteries 1445-1447 

Edison-Lalande cell 1444-1445 

Fuller cell : 1442-1444 

Gravity 1434-1442 

Hydrometer 1439 

Ingredients 1435-1436 

Leclanche cell 1432-1434 

Open circuit 1430 

Planimeter 545-547 

Playford stoker 202-204 

Power test diagrams 506-510 

Calculations 539-548 

Powell lubricator 570-574 

Prescott steam pump 152-154 

Producer gas 751-753 

Properties of saturated steam 278-282 

Q 

Quadruple riveted butt joints 98-102 

R 

Rateau Steam Turbine 681-691 

Action of steam in 681-685 

Principles of * 681 

Regenerator for low pressures 685-691 

Reeves Gas Engine 792-795 

Governor 794 



L Index 

Jump spark for ignition 794-795 

Lubrication of 795 

Methods of construction 792-794 

Water jacket for cylinder 794 

Refrigeration 854-928 

Absorption process 899-918 

Brine — composition of i :...,,.. 911 

Catechism on . .921-928 

Compression system .859-899 

Consolidated ice machine .880-886 

Charging new system 913-914 

De Lavergne refrigerator .872-878 

Generator .907-909 

Linde ice machine 863-872^ 

Recce's improved apparatus. .903^905 

Systems of refrigeration ........... 858 

Thermo-dynamics — two first laws 854 

Wet and dry refrigeration .860-862 

Work of a refrigerating machine 857 

Reidler-Stumpf Steam Turbine °. ......... 693-696 

Action of steam in 696 

Blades — stationary and moving. .693-696 

Method of construction , 693 

Reynolds Long Range Cut-off Engine 403-411 

Setting valves of ; 410-41 1 

Riveted Joints — Boiler 90-1 16 

Rochester Force Feed Lubricator — 576-577 

Roney Stoker : . . 209-213 

Rotary Converters 1277-1289 

Bucking — causes of 1286-1287 

Functions of , 1277-1279 

Insulation of frame 1283-1284 

Oscillators for 1287-1289 

Principles of action 1280-1283 

Repairs to armatures 1286 

Rules for erection 1283-1286 

Russell Shaft Governor 431-433 

Safety Valves 135-142 

Sensible Heat 295-297 



Index 

. Series Wound Dynamo 1068-1069 

Shaft Governors 428-438, 457 

Armington and Sims 435-438 

Atlas 433-435 

General principles of 428-433 

Russell 431-433 

Shunt Wound Dynamo 1069 

Smith Gas Producer 759-762 

Snow Gas Engine 766-779 

Inlet, and cut-off mechanism 77^-779 

Mixing chamber 77^-777 

Speed regulation 776 

Sparking at Brushes — Causes of 1061, 1065-1068 

Specific Heat 294-295 

Stationary Boilers — Types of 1-75 

Steam 302-316 

Catechism on 313-316 

Density of 305 

Dry 304, 305-306 

Flow of — through pipes .310-312 

— from a given orfice 312-313 

Generation of 303 

In its relation to the engine 306 

Nature of 302-303 

Radiation of heat from 306-309 

Relative volume of 305-306 

Total heat of 304 

Wet 304 

Steam Consumption 521-527 

Steam Gauges 132-134 

Steam Engines , .351-580 

Catechism on .368-371 

Classes of 351-352 

Condensing engines 351-364 

Cross compound 365-366 

Multiple cylinder engines 364 

Number of expansions 367 

Steam jacket , 367-36S 

Triple expansion 366-367 



Index 

Water required for condenser 356,360-363 

Steam Turbine 581-710 

Blade— form of 586-587 

Catechism on 703-710 

Development of 583-585 

Disposal of exhaust 697-703 

Principles explained 581-585, 663-664 

Stuffing boxes 587-592 

Parsons 585-589 

Rateau 589-591 

Schulz 588 

Speed regulation 591-592 

Steam Turbines — Allis-Chalmers .649-662 

Curtis 61 1-632 

De Laval 633-634 

Hamilton-Holzwarth 663-679 

Rateau 681-691 

Reidler-Stumpf .693-696 

Westinghouse-Parsons 593-610 

Stirling Water Tube Boilers. .21-28 

Circulation of water in .25-26 

How supported . 21 

Operation of .27-28 

Steam and mud drums . . .21-22 

Tubes — method of connecting 22-23 

Storage Batteries 1447-1454 

Action of 1449-1450 

Advantages of 1447 

^ Chloride accumulator 1451 

Charging 1448-1449 

Construction of I447, 1449-1452 

Edison cell 1453-1454 

Superheater — Steam 173-176 

Switchboard 1224-1364 

A. C. generator panel 1235-1237 

A. C. outgoing panel 1237-1241 

Arc switchboards 1253 

Catechism on 1358-1364 

D. C. feeder panels 1231-1233 



Index 

D. C. generator panels I224-12SS 

Equalizer connections 1227 

Exciter panels 1247-1251 

Functions of instruments 1235-1237 

Horizontal rows of holes 1253 

Induction motor panel 1254 

Maintenance of 1317-1319 

Positive line wires 1253-1255 

Step-up transformers 1244 

Throwing in a generator 1233-1235 

Transferring currents 1255-1259 

Vertical rows of holes 1253 

Switchboards — Thomson-Houston Series Arc 1253-1259 

Western Electric Co.'s Series Arc 1259-1260 

T 

Tabor Indicator 467-468 

Thermometers — Comparison of 289-290 

Thermo-Dynamics — First Law of i 292 

Theoretical Clearance .527-531 

Theoretical Expansion Curve 449, 531-536 

Thomson-Houston Dynamo 1098-1 109 

Operation of i loi-i 105 

Regulator 1104 

Rheostat 1 106-1 109 

Setting the cut-out 1098-1 103 

Starting — rules of 1 109 

Table of leads 1 102 

Thomson-Houston Arc Lamp 1415 

Adjustments of 1417-1418 

Alternating current arc 1422 

Directions for trimming 1418 

Operation of 1415-1417 

Series arc — action of 1419-1422 

Total Heat of Evaporation 298 

Tower Gas Engine • 788-792 

Construction of 789-790 

For heavy duty 788 



Index 

Governor ► . . . v. 790 

Governor valve 791 

Ignition 791-792 

Rating and weight of 7^9 

Valve — how operated 790-791 

Transformers 1260-1277 

Allis-Chalmers transformers 1270-1277 

Auto transformers 1268-1270 

Catechism on 1289-1291 

Cooling 1268-1271 

Efficiency of 1265-1268 

Exciting current 1265 

Principles of .1260-1264 

Step-up or step-down transformers 1264 

Transformer Oil * . . . 1396-1399 

Triumph Ice Machine .878-880 

Description of parts .878-879 

Piston rod packing .879-880 

Tubular Boiler 1-3 

Setting of 61-65 

U 

Underwriters' Rules 1454-1474 

Conductors 1458-1461 

Generators 1454-1458 

Lightning arresters 1465-1466 

Motors 1467-1472 

Railway power plants 1472-1473 

Resistance boxes — equalizers 1463-1465 

Switchboards ^ 1461-1463 

Transformers 1473-1474 

Unequal cut-off 495-498 

V 

Vacuum 447-448 

Valve Adjustment 373-403 

Valve Gear of Corliss Engines 396-398 



NOV 28 1913 



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starting troubles. With numerous tables, 
useful rules and formulae, wiring diagrams 
and over329illustrations. 

Special efforts have been put forth to 
treat the subjects of ignition, and igni- 
tion devices, in a manner befitting their 
im'-ortance. A large section has been 
devoted to t ese subjects, including bat- 
teries, primary and secondary, magnetos, 
carburators, spark plugs, and in fact all devices used in connection with 
the production of the spark. Power transmissio is thoroughly discussed, 
and the various {systems of transmitting the power from the motor to the 
driving axle are analyzed and compared. 

The perusal of this work for a few minutes when troubles occur, will 
often not only save time, money, and worry, but give greater confidence 
in the car, with regard to its going qualities on the road, when properly 
and intelligently cared for. 

A WORD TO THE WISE 

The time is at hand when any person caring for and operating any 
kind of self-propelling vehicle in a public or private capacity, will have to 
undergo a rigid examination before a state board of examiners and secure 
a license before they can collect their salary or get employment. 

Already New York State has enacted such a law and before long, with 
a positive certainty every state in the Union will pa»s such an ordinance 
for the protection of life and property. 

Remember this is a brand new book from cover to cover, just from 
the press — New Edition — and must not be confounded with any former 
editions of this popular work. 

Sent prepaid to any address ^ipon receipt of price 

FREDERICK J. DRAKE & CO., Publishers 

1325 Michigan Avenue, ... CHICAGO, U. S. A. 




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LIBRARY OF CONGRESS 

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